6th July 2021

Adaptation and Resilience

Afternoon Plenary

The Language of Risk: Optimizing Choices to Build Effective Climate Resilience

Dr Tom Philp, Chief Executive Officer, Maximum Information and Dr Helen Greatrex, Assistant Professor in Remote Sensing and Geospatial Analysis, The Pennsylvania State University

The global re/insurance industry is well-versed in catastrophes. While always deleterious and sometimes incapacitating, a large part of the industry would, paradoxically, cease to exist without them. With this fundamentally existential relationship to catastrophic events, over the course of half a millennium the industry has developed an entire language and culture for quantifying these risks. Although slightly reductive, the quantification can be expressed in the following simple form:


Risk = f(Hazard, Exposure, Vulnerability)


This talk aims to deconstruct the meaning behind these terms and, in a world in which infinite research is impossible, to highlight both the value of a holistic risk perspective, along with the dangers of isolated reasoning, when constructing hazard research that aims to improve societal resilience. Finally, the talk will shine a light on real-world hazard to risk attachment points that are of crucial importance for building resilience in the face of a changing climate.


Forecasting Impactful Flooding from Tropical Cyclones to Support Humanitarian Operations

Dr Linda Speight, Researcher in Applied Flood Forecasting, University of Reading


In the absence of local forecasts, or where such information is fragmented or vulnerable to disruption during major events, global forecasting systems can provide effective information to support decision making.

This presentation will explore the evolution of flood bulletins funded by the UK Foreign and Commonwealth Development Office (FCDO) designed to support humanitarian response to major events. Originally piloted during Tropical Cyclone Idai in Mozambique in 2019, the collaborative team including University of Reading, University of Bristol, ECMWF and HR Wallingford have now produced bulletins for Tropical Cyclones Idai, Kenneth, and Eloise in Mozambique and Hurricane Iota in Central America.

The iterative process of developing the bulletins has highlighted valuable questions for the atmospheric science community including;

  • how can global forecasting capability be used to support and build the capacity of local forecasting systems?

  • How can scientific expertise contribute to improve the useability of global forecasts for decision making?

  • What other information is needed beyond global flood models to support humanitarian response?

Climate Change Adaptation in Disasters and Conflict: What is Happening and Where?

Professor Erin Coughlan de Perez, Dignitas Associate Professor, Tufts University and Senior Advisor, Red Cross Red Crescent Advisor

People living in conflict-affected areas are uniquely vulnerable to climate and weather extremes. Basic services, such as healthcare and transport systems, are often not available. Yet these are precisely the regions where we have the largest gaps in knowledge about climate and weather, and the least developed systems to forecast impact and warn people in advance of extreme events. There are several critical and urgent adaptations for these regions, including early warning systems and climate resilient development, and the meteorological community will be a vital actor in making these adaptations possible.

Beyond Limit Values - The Need to Rethink our Air Pollution Policies

Dr Gary Fuller, Senior Lecturer in Air Quality Measurement, MRC Centre for Environment and Health, Imperial College London

According to the World Health Organisation, air pollution exposure is a global health emergency. We began managing air pollution long before we began to address climate change. Air pollution management has evolved since Victorian times. It  began with controls on specific industries, progressed to regulations covering air pollution emissions across a town or city and now where we have legal standards for the quality of outdoor air. Today campaign groups are asking for the UK government to  tighten these standards by incorporating World Health Organisation Guidelines into UK law. This was also supported by the coroner who looked into the tragic death of Ella Kissi Deborah. However, focusing on the attainment of limit values can lead to unintended consequences. The growing evidence of life-course impacts and a lack of a zero-effects threshold should prompt us to change the way that we manage air pollution. A new approach is needed to reduce the impacts of air pollution across all communities and to ensure that our air pollution and climate policies are aligned and optimised for health.


Room One​ - Climate

State of the UK Climate 2020

Mike Kendon, Climate Information Scientist, Met Office, National Climate Information Centre

The Met Office National Climate Information Centre (NCIC) are responsible for the UK’s national climate monitoring capability. The annual State of UK Climate report present the latest summary statistics of observations from the UK’s land surface network for the year against long-term averages, while national climate series, extending back to the 19th century, provide longer-term context. We discuss trends, variations and extremes in these climate records which are based mainly on the 1km resolution HadUK-Grid dataset. We include brief summaries of noteworthy weather events during the year, a short section on phenology produced by the Woodland Trust using citizen science data, and we take an early look at the next set of standard long-term averages for 1991-2020.

Has the Risk of a 1976 North-West European Summer Drought and Heatwave Event Increased Since the 1970s Due to Climate Change?

Dr Laura Baker, Research Scientist, NCAS, University of Reading

In the summer of 1976, north-west Europe experienced an exceptional heatwave and drought, which impacted agriculture and public water supply. We aim to assess whether the likelihood of the event in the present-day climate has changed since 1976 due to climate change. The analysis focuses on the England and Wales region, which was particularly badly impacted. Three key factors contributing to the extreme summer are identified: the dry preceding winter-spring period, the dry summer and the hot summer. We use two different event attribution methods to evaluate the change in the probability of the event: one using CMIP5 coupled climate models, and one using HadGEM3-A atmosphere-only simulations conditioned on the 1975/75 sea surface temperatures. This is the first time that this method has been used to evaluate how the risk of a historical extreme event has changed since it originally occurred. We find a significant increase in the probability of a summer at least as hot as 1976 between 1970s and the present-day climate, but no significant change in the probability of an extreme dry winter--spring or an extreme dry summer. However, the joint probability of an extreme dry winter-spring followed by an extreme hot summer, and the probability of an extreme hot and dry summer, are both found to have increased significantly between the 1970s and the present day climate. 

Characterising and Quantifying the UK Climate Change Commitment over the 21st Century

Chris Smith, Research Fellow, University of Leeds

The climate change commitment is the unavoidable future climate change resulting from inertia in the geophysical and socio-economic systems. This is the bare minimum that nations and organisations must plan for in order to build a climate resilient future. However, the climate change commitment is poorly characterised and quantified at the regional scale. We use CMIP6 climate models and the FaIR simple climate model to estimate the UK climate change commitment over the 21st Century. Firstly, we assess the adequacy of 42 CMIP6 models in reproducing historical UK climate (annually, and in winter and summer) using spatial correlations and absolute values of temperature and precipitation compared to the HadUK-Grid Gridded Climate Observations (on a 60km grid over the UK). This narrows the CMIP6 ensemble down to 10 independent models that best reproduce UK historical climate. Then, we apply a pattern scaling technique to express UK temperature and precipitation change as a function of global mean temperature change in each of the 10 CMIP6 models’ SSP5-8.5 projection. We then use the FaIR model to simulate different global commitment scenarios that are combined with the results from the 10 CMIP6 models to estimate the UK climate change commitment over the 21st Century.

The Effects of Climate Change on the World’s Monsoons

Dr Andrew Turner, Associate Professor of Monsoon Systems, National Centre for Atmospheric Science and University of Reading

Monsoons supply most of the rainfall to large regions of the tropics and affect the lives of billions of people.  This talk reviews the latest assessments of monsoon climate change, including progress over generations of climate models.  Observed rainfall trends in the global monsoon are discussed, as well as attribution to anthropogenic factors including aerosol emissions, which lead to considerable uncertainty.  The latest future projections are presented, including from the recent CMIP6 models, which feature larger climate sensitivities than their predecessors.  As we look forward to the release of the IPCC Sixth Assessment report, the major uncertainties in near-term future projections are also discussed, including the roles of coupled modes of internal variability and aerosol emissions patterns, with a focus on the South Asian monsoon region.


Room Two​ - Air Quality and Composition

 The Impact of Future Climate Change Mitigation Scenarios on Air Pollutants and Climate: The Potential for Co-Benefits

Dr Steven Turnock, Senior Scientist, Met Office Hadley Centre

The major air pollutants, particulate matter (aerosols) and ozone, are important in terms of their impact on human health and they are also near term climate forcers (NTCFs) that influence the magnitude and rate of climate change. The Shared Socio-economic Pathways (SSPs) used in the 6th Coupled Model Intercomparison Project (CMIP6) cover a wide range of future trajectories in both greenhouse gases and air pollutant precursors. This has allowed for an improved assessment of how future air pollutant emission controls and climate mitigation measures will impact future regional air pollutant concentrations. Here we use an ensemble of global composition climate models that participated in CMIP6 to assess future changes in air pollutants across different world regions for different future pathways spanning a range of climate and air pollutant mitigation. Air pollutants are reduced across most regions in the strong mitigation scenarios due to emission reductions and climate mitigation whereas, air pollutants remain closer to present day values for those pathways which have weaker mitigation measures. Additional sensitivity experiments with a single model explored the impacts that individual mitigation measures had on air quality and climate. Strong co-benefits to both air quality and climate are obtained by targeting methane in conjunction with emissions of air pollutant precursors. If methane concentrations are not reduced but other aerosols and O3 precursors are, then there are still benefits to air quality, but the climate forcing is negatively impacted, mainly due to aerosol reductions.  The results highlight the need for concerted efforts to mitigate both greenhouse gases and air pollutant emissions, allowing for maximum benefits to both air quality and climate.

The Role of Aerosol Process Representation in Uncertainty in the North Atlantic Region in CMIP6

Dr Laura Wilcox, Associate Professor, NCAS, University of Reading

Previous studies have shown that anthropogenic aerosol emissions drive a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) in CMIP6 historical simulations that was not simulated in the CMIP5 multi-model mean. The strength of the CMIP6 AMOC trend has been linked to the strength of the aerosol forcing, with the inclusion of aerosol-cloud interactions accounting for a large proportion of the difference between CMIP5 and CMIP6. However, there is large uncertainty in the magnitude and distribution of aerosol effective radiative forcing in CMIP6. Understanding this uncertainty is important for the interpretation of simulated AMOC variability. 

We present an evaluation of the atmospheric variables with the potential to influence AMOC changes in CMIP6 historical and AMIP simulations, including downwelling shortwave radiation, surface heat fluxes, surface air temperature, and precipitation. We examine the links between aerosol effective radiative forcing, the magnitude and pattern of biases in the mean and trends in modelled quantities, and the complexity of the representation of aerosol chemistry and aerosol-cloud interactions. Using these results, we highlight areas where model diversity in the representation of aerosol process may be particularly important for uncertainty in simulations of North Atlantic climate. 

Quantifying Air Quality Impacts of Greenhouse Gas Removal Technologies

Dr Maria Val Martin, UKRI Future Leaders Fellow, University of Sheffield

The United Nations (2018) concluded that delivering on the Paris Climate Agreement requires urgent reductions in greenhouse gas (GHG) emissions and use of large-scale CO2 removal (CDR) strategies. Land-based CDR strategies include, for example, afforestation/reforestation, bioenergy crops, enhanced rock weathering (EWR) and wetland/peatland restoration and widespread implementation of these approaches will have consequences for air quality (AQ), and human health that have so far been overlooked. ERW, involves applying crushed silicate rock (e.g., basalt) to soils to sequester carbon, and is potentially feasible for large-scale deployment with managed croplands and forestry plantations. Here we present an analysis of the effect of ERW with croplands on soil nitrogen emissions (NO, N2O and NH3) and its further implications for air quality and climate feedbacks.  We use the global Community Earth System Model (CESM2), with an improved soil nitrogen emission scheme, and an empirical parameterization to simulate changes from silicate rock applications.  We will discuss implementations in CESM2 and results from a series of modeling experiments designed to quantify the potential AQ impacts with human and crop health consequences, if ERW was implemented at large-scale to help deliver net-zero. 


The Refinement of an Ensemble of Volcanic Ash Forecasts using Satellite Retrievals

Dr Antonio Capponi, Senior Research Associate, Lancaster Environment Centre, Lancaster University

Volcanic ash clouds generated by explosive eruptions pose a significant hazard for aviation, and accurate modelling of ash dispersal is fundamental for assessing flight risks. However, Volcanic Ash Advisory Centers (VAAC) forecasts remain deterministic and lack quantification of the uncertainty that arises from the estimation of eruption source parameters, meteorology and uncertainties within the dispersion model used to perform the simulations. Quantification of these uncertainties is fundamental and could be achieved by using ensemble simulations.

Here, we explore how ensemble-based forecasts — performed using the Met Office dispersion model NAME — together with sequential satellite retrievals of ash column loading, may improve forecast accuracy and uncertainty characterization.
We have developed a new filtering procedure for evaluating a series of ensembles based on their agreement with the satellite retrievals available at the time. A 1000-members a priori ensemble is passed through a filter of verification metrics and compared with the first available set of satellite observations. Members far from the observations are rejected. The members within pre-defined limits of acceptability are used to resample the parameters and design a posterior ensemble to compare with the next available set of satellite observations. The filtering process is applied whenever new satellite observations are available, to create new posterior ensembles propagating forward in time, until all available observations are covered.

We applied the method to the recent Raikoke eruption, which occurred on the 22nd July 2019, to show how ensemble forecasts, refined using satellite observations, can highlight the importance of quantifying uncertainties and help in identifying the parameters that may contribute most to the uncertainty


Room Three​ - Weather

IMPROVER – Probabilistic Post-Processing of Today’s Numerical Weather Prediction Systems

Ken Mylne, Head of Verification, Impacts and Post-Processing, Met Office

A fully probabilistic post processing system called IMPROVER has been developed at the UK Met Office. IMPROVER provides frequently updated probabilistic gridded forecasts, as well as forecasts for point locations, for input into automated forecast generation and for users such as operational meteorologists. Although the outputs are probabilistic, a deterministic interpretation can be extracted if required.

The scientific rationale behind this endeavor is the need to make more optimal use of the current and future generations of convection-allowing Numerical Weather Prediction (NWP) models and ensembles. The aim is to provide seamless, calibrated, probabilistic forecasts that are a blend of NWP models/ensembles from nowcasting to medium range. Today’s NWP systems offer not only many ensemble members but also frequent updates making it very difficult for users to manage the data and exploit latest information, so a key capability of IMPROVER is the frequent cycling, providing a continuously updated forecast blending the most recent available data. 

Several key scientific benefits arise from the probabilistic approach on top of the capability to provide probabilistic outputs. Probabilities allow much simpler and effective blending with older forecasts or between different models/ensembles. We have introduced a variety of probabilistic neighbourhood methods to account for the inherent limited predictability at small scales. Some of these can incorporate topographic variation which is particularly important for variables such as rain, sleet and snow or fog. The ensemble-probabilistic approach has also enabled the use of ensemble calibration methods, which can not only improve skill and spread, but create a much more seamless transition between models/ensembles at different resolutions.

The system is built with a modular software framework that allows flexibility for future development and includes verification at every stage of the processing. IMPROVER is now routinely running with operational support and is expected to become fully operational in 2022. This presentation will describe the scientific vision and current IMPROVER capability and look to further developments to come. 

Using Co-Production to Improve the Appropriate Use of Sub-Seasonal Forecasts in Africa
Dr Linda Hirons, Research Scientist, NCAS, University of Reading

Forecasts on sub-seasonal to seasonal (S2S) timescales have huge potential to aid preparedness and disaster risk reduction planning decisions in a variety of sectors. However, realising this potential depends on the provision of reliable information that can be appropriately applied in the decision-making context of users. There is increasing evidence that doing this effectively requires iterative collaboration across a range of disciplines and stakeholders, through a process known as co-production. This study describes results from the African SWIFT (Science for Weather Information and Forecasting Techniques) S2S testbed which, through methods of co-production, brings together researchers, forecast producers and users from a range of African and UK institutions. It addresses the need for improving the appropriate use of real-time S2S forecast information in decision making across Africa.

Satellite-Based Nowcasting of West African Storms

Ralph Burton, Research Scientist, NCAS

There is an urgent need for improved predictions of high-impact weather in Africa, particularly of the heavy rain and floods that can result from intense, large or slow-moving systems of deep moist convection. Numerical weather prediction is inherently challenging in the tropics and in Africa this is compounded by a lack of in-situ observations for model initialisation. As a result, skill of NWP for convective rainfall is very often very low, even at short lead times. Nowcasting provides a complementary approach to NWP, with the often large and long-lived nature of the high-impact convective events making forward extrapolation of observed systems valuable. In this study a freely-available nowcasting package is used to assess the potential to provide nowcasts of convective rain rate. We demonstrate that a simple approach of "optical flow" can have useful skill at 2 hours lead time on a 10 km scale, and 4 hours at larger scales (200 km). Diurnal sensitivity is explored. Such nowcasts, if implemented operationally, would be expected to have significant benefits.

Impact of Sudden Stratospheric Warmings on United Kingdom Mortality

Prof Andrew Charlton-Perez, Professor of Meteorology, University of Reading

Sudden stratospheric warmings (SSWs) during boreal winter are one of the main drivers of sub‐seasonal climate variability in the Northern Hemisphere. Although the impact of SSW events on surface climate and extreme weather has been clearly demonstrated, the impact of the resulting climate anomalies on society has not been so widely considered. In the United Kingdom (UK), SSWs are associated with cold weather, which is linked to significant increases in mortality. In this presentation we will quantify the impact of SSW events on mortality in the UK and show how sub-seasonal forecasts might be used to better prepare for these extreme events. In the first part of the presentation, we show how epidemiological models can be used to construct a daily time series of UK deaths attributable to cold weather. Following the 15 SSWs during the period 1991-2018, SSW associated mortality peaks between 3 and 5 weeks after SSW central date and leads to, on average, 620 additional deaths. The large and delayed impact of SSW events on mortality in the UK provides the motivation for the second part of the talk. Using the 2018 'Best from the East' cold wave as an example, we will show how sub-seasonal forecasts during SSW events can provide 'windows-of-opportunity' to allow the health system to mitigate the impact of similar cold events.


Short Talks ​

Mid-latitude Dynamics 2

Geopotential Jet Regimes - A Hybrid Approach to Understanding Euro-Atlantic Non-Linearity

Josh Dorrington, PhD Researcher, University of Oxford

The Euro-Atlantic circulation is notoriously difficult to model and predict, subject to substantial external forcings, and dominated by nonlinear internal variability. The two main modes of nonlinearity in the Euro-Atlantic are the variations in latitude of the eddy driven jet, and the onset of persistent anticyclonic patterns. Both these phenomena exhibit regime behaviour: some latitudes or locations are preferred over others, forming a discrete set of qualitatively distinct states that can be used to understand the underlying continuous flow. Circulation regimes - which focus on capturing the preferred locations of anticyclonic blocking anomalies - have historically proven difficult to identify robustly, and assessing regime number and statistical significance is challenging. Meanwhile, jet latitude regimes are less ambiguous and more robust to analysis in different datasets, with visible trimodality in the p.d.f.

By adopting a hybrid approach, which removes the linear, highly variable, impact of jet speed from the geopotential height field prior to clustering, we obtain so-called "geopotential jet regimes", which show much greater stability, and strongly prefer three circulation patterns. By reducing sampling variability in the underlying regime patterns, this new regime framework is better suited to intermodel comparisons, and for evaluating forced and internal regime variability. Here I will demonstrate the application of this new regime framework to state-of-the-art GCM simulations, and provide a new assessment of the impact of climate change on future regime patterns.

Northern Hemisphere Blocking Simulation in HadGEM3-GC4 Compared to the Climate Model Intercomparison Project Phase 5 and 6 Multi-Model Ensemble
Reinhard Schiemann, Associate Professor, NCAS, University of Reading

Global climate models (GCMs) are known to suffer from biases in the simulation of atmospheric blocking, and this study provides an assessment of how blocking is represented by the latest generation of GCMs. It is evaluated (i) how historical CMIP6 (Climate Model Intercomparison Project Phase 6) simulations perform compared to CMIP5 simulations, (ii) how horizontal model resolution affects the simulation of blocking in the CMIP6-HighResMIP (PRIMAVERA – PRocess-based climate sIMulation: AdVances in high-resolution modelling and European climate Risk Assessment) model ensemble, which is designed to address this type of question, and (iii) how the current development version of HadGEM3 – GC4 – performs compared to these two multimodel ensembles.

Two blocking indices are used to evaluate the simulated mean blocking frequency and blocking persistence for the Euro-Atlantic and Pacific regions in winter and summer against the corresponding estimates from atmospheric reanalysis data. There is robust evidence that CMIP6 models simulate blocking frequency and persistence better than CMIP5 models in the Atlantic and Pacific and during winter and summer. As for the sensitivity of simulated blocking to resolution, it is found that the resolution increase, from typically 100 to 20km grid spacing, in most of the PRIMAVERA models, which are not re-tuned at the higher resolutions, benefits the mean blocking frequency in the Atlantic in winter and summer and in the Pacific in summer. Simulated blocking persistence, however, is not seen to improve with resolution.

Our results are consistent with previous studies suggesting that resolution is one of a number of interacting factors necessary for an adequate simulation of blocking in GCMs. The improvements reported in this study hold promise for further reductions in blocking biases as model development continues.


Contrasting Dynamics of Short and Long Atmospheric Blocks

Tim Woollings, Professor, University of Oxford

Blocking weather patterns are of particular interest because they are sometimes very persistent, which can lead to prolonged heatwaves in summer and cold events in winter. Here we investigate the mechanisms that contribute to separating long-lived blocks from less persistent ones. A key ingredient is found to be the direction of the Rossby wave-breaking involved in the blocking formation, with long-lived blocks preferentially associated with wave-breaking in the cyclonic sense. Some reasons for this are investigated with a focus on transient eddy feedbacks. Finally, the wave-breaking characteristics of long blocks are found to be well simulated in a climate model ensemble, increasing confidence in the representation of some of the mechanisms underlying these extreme weather events.


Tor Bergeron and the Birth of Synoptic Analysis: Air-Mass Analysis and Antecedents to the Shapiro–Keyser Cyclone Model

Prof David M. Schultz, Professor of Synoptic Meteorology, Centre for Atmospheric Science, and Centre for Crisis Studies and Mitigation, University of Manchester

Tor Bergeron was a key member of the Bergen School of Meteorology that developed some of the most influential contributions to synoptic analysis in the twentieth century: airmass analysis, polar-front theory, and the Norwegian cyclone model. This presentation discusses two aspects of his early career.  First, Bergeron’s 1928 PhD dissertation articulated for the first time and in great detail the Bergen analysis methods, particularly air-mass analysis.  For the first time, we present an English translation of his dissertation.  Second, Bergeron’s published analyses revealed three components of cyclone structure that would later be constituted into the Shapiro–Keyser cyclone model in 1990.

The Life Cycle of Meridional Heat Flux Peaks

Andrea Marcheggiani, PhD Student, University of Reading

Covariance between meridional wind and air temperature in the lower troposphere quantifies the poleward flux of dry static energy in the atmosphere; in the mid-latitudes, this is primarily effected by baroclinic weather systems. It is shown that strong covariance between temperature and meridional wind results from both enhanced correlation and enhanced variance, and that the two evolve according to a distinct temporal structure akin to a life-cycle. Starting from a state of low correlation and variance, there is first a gradual build up to modal growth, followed by a rapid decay at relatively low correlation values. This life-cycle evolution is observed most markedly over oceanic regions, and cannot be explained on purely statistical grounds.


Extracting Likely Scenarios from High Resolution Forecasts in Real-Time
Kris Boykin, PhD Student, University of Reading

Currently, the Met Office produces a high-resolution ensemble forecast, MOGREPS-UK, which is used for forecasting the risk of high impact weather and issuing severe weather warnings.  However, each ensemble produces large amounts of complex data which the forecasters cannot easily digest in real time.  Therefore, a lot of weight in forecasts issued is placed on the single “deterministic run” which cannot convey information on the range of possible outcomes or their forecast probabilities.  As the speed and accuracy of high impact forecasting is vital for safety and livelihoods alike, this project aims to reduce the amount of data a forecaster must work through before being able to provide a forecast.  By using clustering, we can determine a few distinct plausible scenarios among the members of the ensemble, reducing the amount of data a forecaster must go through and by extension, the amount of time it will take to issue a forecast of the event.  The method focuses on K-medoids clustering and the results presented will focus on traceability of the clusters through time.


Tropical Meteorology 2

How Interactions Between Tropical Depressions and Western Disturbances Affect Heavy Precipitation in South Asia

Kieran M Hunt, Senior Research Scientist, NCAS, University of Reading

Interactions over South Asia between tropical depressions (TDs) and extratropical storms known as western disturbances (WDs) are known to cause extreme precipitation events, including those responsible for the 2013 floods over northern India.In this study, existing databases of WD and TD tracks are used to identify potential WD--TD interactions from 1979–2015; these are filtered according to proximity and intensity, leaving 59 cases which form the basis of this work. Synoptic charts, vorticity budgets, and moisture trajectory analyses are employed to identify and elucidate common interaction types among these cases.Two broad families of interaction emerge. Firstly, a dynamical coupling of the WD and TD, whereby either the upper- and lower-level vortices superpose (a vortex merger), or the TD is intensified as it passes into the entrance region of a jet streak associated with the WD (a jet-streak excitation). Secondly, a moisture exchange between the WD and TD, whereby either anomalous moisture is advected from the TD to the WD, resulting in anomalous precipitation near the WD (a TD-to-WD moisture exchange), or anomalous moisture is advected from the WD to the TD (a WD-to-TD moisture exchange).Interactions are most common in the post-monsoon period as the subtropical jet, which brings WDs to the subcontinent, returns south; there is a smaller peak in May and June, driven by monsoon onset vortices. Precipitation is heaviest in dynamically-coupled interactions, particularly jet-streak excitations. Criteria for automated identification of interaction types are proposed, and schematics for each type are presented to highlight key mechanisms.

Indian Monsoon Low-Pressure Systems in Subseasonal-to-Seasonal Prediction Models

Akshay Deoras, PhD Student, Department of Meteorology, University of Reading

Indian monsoon low-pressure systems (LPSs) are cyclonic vortices that typically develop within the quasi-stationary monsoon trough, and produce substantial summer monsoon precipitation over India. They have triggered many high-impact floods, causing adverse socio-economic impacts across the Indian subcontinent. It is therefore essential to understand LPS predictions on the time scales of numerical weather prediction and extended-range models. Here, we use a feature-tracking algorithm to identify LPSs in all ensemble members of eleven models of the Subseasonal-to-Seasonal (S2S) prediction project during a common reforecast period of June–September 1999–2010. Forecast verification statistics for the frequency, track position, intensity and precipitation of LPSs are produced. In addition, composite horizontal and vertical structures of many dynamic and thermodynamic fields are generated. These results are then compared with ERA-Interim and MERRA-2 reanalysis datasets.

The results show that all S2S models underestimate the frequency of LPSs as well as their precipitation contribution to the summer monsoon. Furthermore, errors in the simulation of LPSs influence the pattern of total precipitation biases in all S2S models. Whilst LPS tracks are simulated by all models, large biases are observed in the BoM, CMA, ECCC and HMCR models. The CMA model exhibits the largest position error, and the intensity of LPSs is overestimated (underestimated) by most models when verified against ERA-Interim (MERRA-2). The region of maximum precipitation as well as the lower-tropospheric cold core is not well simulated by many models, particularly the HMCR model. The vertical structures of anomalies of relative vorticity and moist-static energy are shallower and weaker in all S2S models than in ERA-I and MERRA-2.

Patterns of 2016 Indian Monsoon Convection in the Met Office Unified Model and Ground Weather Radar Observations

Alex Doyle, PhD Candidate, Department of Meteorology, University of Reading

Indian monsoon convection brings a large amount of India’s annual rainfall, but remains poorly understood in the context of the large-scale monsoon circulation. Here, patterns of convection derived from a network of ground weather radars are compared directly to convective permitting Met Office Unified model runs, for the period 19 June–11 July 2016. We present the spatial patterns of precipitation and convection in the model over India, before comparing against radar observations in terms of storm height, size, and intensity. We also focus on the representation of the diurnal cycle of convection in different regions in both model and radar data. This is the first analysis of its kind performed over India, and will help enable a better understanding of model performance in different convective and large-scale states. 

Effect of Moisture and Evaporation-Wind Feedback on the Dispersive Characteristics of Madden Julian Oscillation

Kartheek Mamidi, PhD Student, Dept of Physics, Central University of Kerala

Madden Julian Oscillation is the low frequency eastward propagating variability, which has an enormous impact on other tropical variabilities as well as global weather and climate. MJO is one of the dominant modes of slowly moving equatorial moisture variability, which was discovered nearly half a century ago and had a large section of theories associated with its observed features. An underlying mechanism is proposed here to understand the most fundamental characteristics of MJO, such as its eastward propagation and its preferable planetary-scale wavenumber. The dynamical framework formulated here is a single layer linear shallow water model with equatorial beta-plane approximation and momentum damping; the horizontal structure consists of a simple first baroclinic mode in the free troposphere. The hypothesis of the present dynamical framework is by treating the tropical atmospheric flow is not in exact quasi-equilibrium with heating profile, which means the moisture dynamics in the tropics is completely governed by the moisture process with moisture relaxation time scale. Our theory's dispersion relation produces the eastward propagating moist dispersive mode, which has similar large-scale characteristics of MJO. The results show that the strength of the moisture convergence feedback makes the eastward moisture mode unstable at planetary wavenumber, and the simulated dispersion relationship agrees with the observed one of the MJO very well, whose frequency is nearly independent of wavenumber k. Therefore this model recovers the peculiar dispersion relation of observed MJO mode (),and it is in consistence with the previous theoretical works. With regard to the growth rate this MJO-like mode is unstable with maximum growth rate at planetary wavelength and decreases slowly with the wavenumber.

Here we also investigated the role of evaporation wind feedback (E-W), the strength of E-W feedback makes the eastward propagating MJO mode slow down at a planetary scale and increases the growth rate. The model also demonstrates the influence of Rayleigh damping on the dispersion properties of produced MJO mode using the same mathematical framework. The sensitivities of these parameters on the model are also discussed.

Historical Variability and Lifecycles of North Atlantic Midlatitude Cyclones Originating in the Tropics
Alexander Baker, Research Scientist, NCAS, University of Reading

North Atlantic tropical and post-tropical cyclones impact midlatitude regions, but the inhomogeneous observational record of the latter stages of tropical cyclones precludes many climatological analyses. The frequency of tropical-origin storms basin-wide is projected to increase under anthropogenic climate change, so establishing confidence in our knowledge of their historical variability and lifecycles—against which climate model simulations may be evaluated—is important. We used a Lagrangian feature-tracking algorithm to identify tropical cyclones that impacted Northeast North America and Europe in seven global reanalysis datasets, distinguishing systems that retained warm-core structures or underwent warm seclusion from those that underwent extratropical transition, acquiring cold-core, frontal structures. Over the last four decades, ~25 % and ~10 % of tropical-origin cyclones made landfall across Northeast North America and Europe, respectively, as warm-core systems, with, on average, higher wind speeds than cold-core systems. Historical warm- and cold-core landfalls also exhibit distinct tracks, likely responding to differing steering flow and midlatitude conditions.


Extremes 2

Temperature-Related Health Risk in the UK

Katty Huang, Postdoctoral Research Fellow, University of Reading; University College London

​Non-optimal ambient temperatures have an adverse impact on human health that results in increased mortality rates following cold spells and during heatwaves. Currently in the UK, the majority of temperature-related deaths are associated with cold exposure, but increasing heat-related deaths are expected in the future due to climate change. As part of the UK Climate Resilience Programme, we quantify the mortality risk associated with temperature exposure at regional levels in the UK, propose a pathway to sub-seasonal forecasting of health risks through association with weather regimes, and examine the impact of climate change on health using UKCP18 climate projections. While future decreases in winter cold-related mortality scales linearly with global warming, heat-related mortality in summer increases at significantly greater rates at higher temperatures compared to moderate warming scenarios, highlighting the importance of limiting global warming to below two degrees.

Downscaling ERA5 to Indoor Temperatures in Ghana

Chloe Brimicombe, Environmental Climate Science PhD Researcher, University of Reading

​Heatwaves are increasing in frequency, duration, and intensity. They were the deadliest hydro-meteorological hazard globally for the last 5 years according to the World Meteorological Organisation. One impact of heatwaves is heat stress which is a build-up of body heat because of exertion and/or the external environment. Evidence about heat stress across Africa including Ghana is sparse and this is particularly the case for the indoor environments such as homes, workplaces and public spaces. Here we make use of indoor temperature observations gathered by the VEWEC project at 10-minute intervals from health facilities within the cities of Accra and Tamale, Ghana. This allows for an assessment of the skill of various methods including both linear regression and machine learning regression techniques for downscaling the ECMWF reanalysis ERA5 2m temperature data set which is gridded at a resolution of 0.25°x0.25° at hourly time steps. This research reveals the potential of different downscaling methods for forecasting indoor temperatures in Ghana with the ultimate goal of developing early warning systems for local heat.

Evaluation of Seasonal Variations of Selected Indices of Human Thermal Comfort in Nigeria

Mojisola O. Adeniyi, Lecturer, University of Ibadan and Muyiwa P. Aajakaiye, Lecturer and PhD Student, Anchor University, Lagos

Thermal heat stress, as an extreme event, has occasioned the mortality and morbidity of many lives across nations, reduced labour productivity and ruined yield potentials among plants and ruminants. Unfortunately, adequate grass root studies using in-situ data necessary to provide the exact environmental thermometry have not been provided. In this study, we acquired primary meteorological data sets from the Tropospheric Data Acquisition Network (TRODAN), Centre for Atmospheric Research, National Space and Development Agency (CAR-NASRDA). The data set covers two successive seasons (wet season, April – October 2009 and a dry season, November, 2009 – March, 2010) with carefully selected five agro-ecological locations in Nigeria (Abuja, Akungba, Port Harcourt, Makurdi and Minna). Result from the analyses of temperature and relative humidity revealed that temperature and relative humidity have divergent relationships in the two seasons. While higher values of temperature were obtained during the dry season, relative humidity was significantly reduced. This pattern was reversed during the wet season for all stations. Thereafter, environmental human thermal comfort indices were calculated using humidex and simplified wet bulb globe temperature (sWBGT). The results obtained displayed spatial and temporal variations (pattern and extent) over the five locations. The dry season presents higher thermal indices than the wet season in all the five stations. Observations further revealed that temperature has a stronger impact on the size and trend of heat index than relative humidity. Linear correlations of the mean values of calculated comfort indices with latitude and elevations give weak correlation. Overall results of the indices suggest tolerable weather but characterised with a minute evidence of warming.

Social Sensing of Heatwaves

James C. Young, Research Associate, University of Exeter

Heatwaves cause thousands of deaths every year, yet the social impacts of heat are poorly measured. Temperature alone is not sufficient to measure impacts and “heatwaves” are defined differently in different cities/countries. In this poster session, we demonstrate the use of Twitter data to analyse the social response to heat during the 2018/2019 heatwave season in the UK, US, and Australia, before investigating how cities in each of the countries uniquely responded to heat. By building upon pre-existing social sensing methodologies, we show that:

1.            In the countries investigated, there is a strong, statistically significant correlation between temperature and Twitter activity. Between the Twitter populations within each country, there is a clear variation of risk perception regarding heatwaves.

2.            On a city scale, spatiotemporal identification of heatwaves through Twitter is possible. Within these cities, the sentiment of tweets uncovers predictable periods of heightened negativity when discussing heatwaves. This provides data on how/when/where a population is most impacted by heat.

3.            Social sensing can complement additional data sources such as emergency response data and health records, facilitating better preparedness to heatwaves whilst allowing for more effective, location-specific mitigation.

The Winter UHI – A Protective Effect? Impacts of the UHI and Urban Heat Mitigation on Health for Present and Future Climate in a European City

Dr Helen Macintyre, Senior Environmental and Public Health Scientist, Centre for Radiation Chemicals and Environmental Hazards, Public Health England, School of Geography, Earth and Environmental Sciences, University of Birmingham

Human health can be impacted by hot or cold weather, which often exacerbates respiratory or cardiovascular conditions and increases the risk of mortality. Urban populations are at increased risk of effects from heat due to the Urban Heat Island (UHI) effect (higher urban temperatures compared with rural ones); recent work suggests that up to half of heat-related mortality in the West Midlands during the 2003 heatwave could be attributed to the UHI.

This has led to investigation of the summertime UHI, its impacts on health, and also the consideration of interventions such as reflective ‘cool’ roofs to help reduce summertime overheating effects. However, far less is known about the UHI in winter, and any potential impacts there may be on health. Additionally, interventions aimed at limiting summer heat would typically be in place year-round, but are rarely evaluated for effects outside of the summer period, and thus their impacts over the year are poorly understood; understanding of the wintertime impacts of such interventions is required to avoid maladaptation.

The West Midlands of the UK, including the city of Birmingham, is a highly urbanised area with a distinct UHI. In this study we use a regional weather model (WRF) with detailed representation of urban areas (Noah-LSM and BEP urban sub-model) to study the UHI in this region in winter, and to examine the impacts of reflective ‘cool’ roof interventions for a cold winter period and compare to previous work for a hot summer. Previous modelling suggested that during heatwaves, cool roofs could reduce heat-related mortality attributed to the UHI by 25%. We show that the winter UHI may have a small protective effect on health in winter (by avoiding 15% of cold-related mortality), and further show that cool roofs do not significantly weaken this protective effect in winter.

Using climate projection data (UKCP18), we further suggest that the benefits of cool roofs may increase in future, with a doubling of the number of heat-related deaths avoided by the 2080s (RCP8.5), and insignificant changes in the impact of cool-roofs on cold-related mortality. This further supports such strategies as effective interventions to protect health, today and in future.

A Novel Way to Monitor Heatwave Deaths

Dr Eunice Lo, Research Associate, University of Bristol

Heatwaves are a serious threat to human life. Every summer, hundreds to thousands of excess deaths are currently estimated during heatwave periods across England alone. To adapt the nation to rising temperatures, it is important to fully understand the impact of heat on human mortality. In this talk, I am going to demonstrate the novel use of epidemiological models to monitor heat-related deaths in regions in England in near real time. This method complements the existing method employed by Public Health England, and it has the potential to be employed by other public health agencies in the world for strengthened heat-health planning.

Future Changes in High-Impact Events in Convection-Permitting Projections

Prof Lizzie Kendon, Scientist, Science Fellow and Manager of Understanding Regional Climate Change, Met Office, UK and Professor in Faculty of Science, Bristol University

Climate projections at very high resolution (km-scale grid spacing) are becoming affordable. These ‘convection-permitting’ models (CPMs), commonly used for weather forecasting, better represent small-scale processes in the atmosphere such as convection and are able to provide credible projections of changes in local weather extremes. At the UK Met Office we have carried out climate change simulations at 2.2km resolution over a pan-European domain, and also the first ensemble of CPM climate projections over a UK domain as part of the next set of UK Climate Projections (UKCP). In this talk I will highlight new understanding of changes in high-impact events from these CPM simulations. This includes changes in the intensity and temporal sequencing of heavy precipitation events, and the increasing contribution from intense organised convective systems to total precipitation across the UK and Europe. I will show the increasing role of slow-moving storms, which are associated with long duration rainfall and hence high precipitation accumulations. I will also discuss new insights into changes in lightning and wind extremes, including sting-jets.


Earth System and Forecast Modelling Tools

High-Resolution Climate Modelling on ARCHER2: Technical Developments and Performance Results

Annette Osprey, NCAS, University of Reading

Not submitted at time of print

Jupyter Notebooks on JASMIN - The JASMIN Notebook Service

Ag Stephens, Head of Partnerships, CEDA, NCAS / STFC / CEDA

Jupyter Notebooks are interactive tools for developing, executing and sharing scientific code and results. They provide an excellent entry-point and communication tool for scientific data analysis. The Centre for Environmental Data Analysis (CEDA) launched a new service in 2020 to support Jupyter Notebooks. The service runs on JASMIN which provides storage and compute facilities to enable data-intensive environmental science.

The JASMIN Notebook Service [1] has the unique capability of enabling access to JASMIN data holdings through an interactive programming environment that runs in a web browser. Users can access curated data sets (such as CMIP6 [2] and Sentinel [3]) and project-specific data via a web browser. The notebooks consist of annotations and Python code to read, process and visualise the data using a collection of common open-source software packages. Each notebook can be shared, often using GitHub, as documented workflows or examples of environmental data processing.

The JASMIN Notebook Service currently provides Python 3.7 with a software environment of data analysis packages installed. Users can add their own environments using package managers such as "conda" and "pip". The service is managed using cloud technologies so that the user is given a ring-fenced resource in which she can develop and run notebooks. Each notebook allows access to data in users home directories (used for personal storage), group workspaces (used for shared project data), and the CEDA Archive (a long term data archive for earth observation and atmospheric data).

CEDA aims to develop a repository of example notebooks to demonstrate the usage of common software and high-profile data sets. This talk will demonstrate the power of notebooks and highlight the advantages of using the JASMIN Notebook Service.

Arrivals Service - Working with Other NERC Data Centres to Share the Load

Samuel Pepler, CEDA Curation Manager, NCSA/CEDA

In 2018 NERC commissioned all the pre-existing NERC data centres as a single service - the Environmental Data Service (EDS). While many of the services we deliver have continued in much the same way as usual, we are now working with the other data centres in a number of ways. One problem we have tackled together is storing large volume datasets. The CEDA Archive has always had to handle large datasets, but increasingly the other data centres in the EDS are being asked to curate large volumes.

The CEDA Archive has expanded its arrivals service where users deliver data for the archive to accommodate data for the other data centres. Staff from the data centre review delivered data, accept it and document it in their specific subject based repository’s catalogue. The main advantage of splitting the storage and documentation functions is that the other data centres increase the capacity to take new larger datasets and at the same time keep cataloguing processes that focus on their specific user communities.


We have already used the system for data from the Polar Data Centre (PDC), The British Oceanographic Data Centre (BODC) and the National Geoscience Data Centre (NGDC). We aim to improve the functionality over time and work on ways to more closely integrate our workflows.

Preparing the UKCA Composition Model for Exascale Supercomputing Applications

Luke Abraham, Principal Research Associate, NCAS & Department of Chemistry, University of Cambridge

The United Kingdom Chemistry and Aerosol model currently forms the composition-modelling capability of the Met Office Unified Model and is used both for climate research and air-quality forecasts. As part of the SPF ExCALIBUR programme, the UKCA model is being prepared for use on future exascale supercomputing architectures. This work will also enable standalone configurations of UKCA to be developed and will allow for UKCA to be coupled to many different modelling systems. We will discuss the current progress, anticipated benefits, and future plans.

Assessing the Quality of State-of-the-Art Regional Climate Information: The Case of the UK Climate Projections 2018

Dr Marina Baldissera Pacchetti, Research Fellow, Sustainability Research Institute, School of Earth and Environment, University of Leeds and ESRC Centre for Climate Change Economics and Policy

We assess the quality of state-of-the-art regional climate information intended to support adaptation decision-making. We use the UK Climate Projections 2018 as an example of such information. Their probabilistic, global and regional land projections exemplify some of the key methodologies that are at the forefront of providing regional climate information for decision support in adapting to a changing climate. We assess the quality of the evidence and the methodology used to support their statements about future regional climate along five quality dimensions: transparency, theory, diversity, completeness and adequacy for purpose. The assessment produced two major insights. First, the main issue that taints the quality of UKCP18 is the lack of transparency. The lack of transparency is particularly problematic if the information is directed towards non-expert users, who would need to develop technical skills to evaluate the quality and epistemic reliability of this information. Second, the probabilistic projections are of lower quality than the global projections. This assessment is a consequence of both lack of transparency in the probabilistic projections, and the way the method is used and justified to produce quantified uncertainty estimates about future climate. We suggest how higher quality could be achieved. We conclude by recommending further avenues for testing the effectiveness of the framework and highlighting the need for further research in user perspectives on quality.


The Role of Aerosols in Weather and Climate


The Role of Aerosol Forcing for Recent Historical Pacific Decadal Variability

Dr Andrea Dittus, Research Scientist, NCAS, University of Reading

Studies have suggested a role for aerosol forcing in contributing to recent historical Pacific Decadal Variability, but results vary across models and studies. Here, we show how aerosol forcing interacts with other external forcings and internal climate variability to generate simulated multi-decadal Pacific variability since the 1980s in models partaking in the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6). A large ensemble of climate model simulations with HadGEM3-GC3.1, where anthropogenic aerosol emissions are scaled by a range of factors, is used to identify the mechanisms driving the response to aerosol forcing in HadGEM3. Our results show a forced response in Pacific surface air temperatures to anthropogenic aerosols in the period 1981-2012 in HadGEM3, associated with a Rossby Wave train across the North Pacific and a weakening of the Aleutian Low. We discuss these results in the context of understanding recent real-world Pacific variability and the role of the Pacific in explaining observed and simulated temperature trends since the 1980s.

What Controls the Historical Timeseries of Shortwave Fluxes in the North Atlantic?

Daniel Grosvenor, NCAS Research Fellow, NCAS, University of Leeds

Using radiative flux calculations and the DAMIP experiments we determine what causes the long-term trends in the shortwave (SW) top-of-the-atmosphere (TOA) fluxes in the UKESM1 and HADGEM coupled climate models for the North Atlantic region and what the implications for aerosol-cloud interactions (ACIs) are. We find that there is a positive SWTOA trend between 1850 and 1970 and then a negative trend between then and 2014. The early period trend is mainly driven by an increase in cloud droplet concentrations (Nd) due to aerosol increases, whereas the trend in the later period is mainly driven by a decrease in cloud fraction caused by greenhouse gas increases. This has implications on the feasibility of using the later period (during which there are useful satellite observations) to evaluate and constrain ACIs. Using nudged simulations where the meteorology can be controlled, we also determine the aerosol effects without any atmospheric circulation feedbacks, thus allowing a partitioning between feedback and non-feedback aerosol effects. In the coupled DAMIP run in which only aerosol forcing is applied we find that feedbacks cause over 50% of the overall SWTOA change.

Extreme Dust Weather over East Asia: Insights from the CAMS Reanalysis and High-Resolution Modeling

Dhirendra Kumar, Research Scientist, NCAS, University of Reading

Constituting more than half of total atmospheric aerosol load, dust aerosols impact air quality, aviation, the energy budget, and hydrological cycles at regional and global scales. Here we identify and compare the key meteorological drivers associated with extreme spring dust storms over East Asia using the ECMWF Copernicus Atmospheric Monitoring Service (CAMS) global reanalysis and high-resolution global climate model (GCM) simulations at 14 km horizontal resolution with parameterized convection. We contrast the meteorology associated with extreme dust storms over the Gobi and Taklamakan deserts to that which occurs when extreme dust storms reach Beijing, further downstream.  Extreme dust storms are identified in CAMS based on either dust aerosol optical depth (DAOD) peaks over the Gobi and Taklamakan deserts or in Beijing. Extreme dust events reaching Beijing are driven by prevailing surface and low-level north-westerlies transporting emitted dust from the source deserts to the far east in association with low-level transient cyclonic systems positioned over northeast China. Contrastingly, extreme dust storms over the Gobi region are dominated by southeasterlies in association with a low-level trough positioned north of the Tarim Basin. For these cases, the dust reaches up to 600hPa vertically in the atmosphere with the events being persistent for 2-3 days. Anomalous large-scale circulation patterns in the mid-troposphere along with their complex interaction with the Tibetan plateau play an important role in steering the dust over the study region. Finally, we evaluate dust emission and transport of extreme dust events in the high-resolution model and compare the characteristics and meteorology associated with them to that identified from CAMS. 

How Does Anthropogenic Aerosol Forcing Drive a Strengthening of the AMOC in CMIP6 Historical Simulations?

Dr Jon Robson, Principal Research Scientist, NCAS, University of Reading

Previous work has shown that anthropogenic aerosol emissions drive a strengthening in the Atlantic Meridional Overturning Circulation (AMOC) in CMIP6 historical simulations over ~1850-1985. However, the mechanisms driving the increase are not fully understood. Previously, forced AMOC changes have been linked to changes in surface heat fluxes, changes in salinity, and interhemispheric energy imbalances. Here we will show that across CMIP6 historical simulations there is a strong correlation between ocean heat loss from the subpolar North Atlantic and the forced change in the AMOC. Furthermore, the model spread in the surface heat flux change explains the spread of the AMOC response and is correlated with the strength of the models’ aerosol forcing.  However, the AMOC change is not strongly related to changes in downwelling surface shortwave radiation over the North Atlantic, showing that anthropogenic aerosols do not directly drive AMOC change through changes in the local surface radiation budget. Rather, by separating the models into those with ‘strong’ and ‘weak’ aerosol forcing, we show that aerosols appear to predominantly imprint their impact on the AMOC through changes in surface air temperature over the Northern Hemisphere and the consequent impact on latent and sensible heat flux. This thermodynamic driver (i.e. more heat loss from the North Atlantic) is enhanced both by the increase in the AMOC itself, which acts as a positive feedback, and by a response in atmospheric circulation.

The Red Sky: Investigating the Hurricane Ophelia Saharan Dust and Biomass Burning Aerosol Event

Dr Kevin P. Wyche, Research Centre Director, Centre for Earth Observation Science, University of Brighton

On 16th October 2017 ex-hurricane Ophelia passed over the UK, bringing with it a unique aerosol loading which caused the Sun and sky to turn a dramatic red colour. Here we use an ensemble of modelling and remote sensing techniques in a ‘top-down, bottom-up’ approach comprising instruments onboard orbital platforms and a ground-based lidar, to interrogate the aerosol-cloud matrix in order to determine its composition and origins. Satellite observations were successfully employed to provide a detailed, holistic ‘snapshot’ (from the ‘top-down’) of the Ophelia weather system with high spatial coverage but low temporal resolution and the ground-based lidar was used to provide complementary, near real-time information (from the ‘bottom-up’) on the types of particles entrained in the air mass as it slowed and passed over the UK. By using top-down measurements from space it was possible to analyse the effect of the embedded aerosol on the light that was being scattered and subsequently the reddening of the Sun. Satellite measurements showed that the aerosol loading of the air mass was high, with an aerosol index over 5, and contained significant levels of CO, up to almost 300 ppbV. Multi-spectral imaging of the system allowed the differentiation of cloud types and identification of regions of aerosol. By using bottom-up lidar measurements it was also possible to observe the temporal evolution, composition and the vertical extent of the aerosol-laden air mass. Combined with back-trajectory modelling, the satellite and ground-based measurements allowed the sources of the aerosol to be determined as Saharan dust uplift and wildfires across Portugal and Spain. The lidar measurements showed that the red sky event comprised two distinct phases. The initial phase was dominated by Saharan dust (volume depolarisation ratio; VCD = 0.15-0.25) and the second by an optically dense layer starting at around 0.7 km comprising a mixture of Saharan dust and biomass burning particles (VDP = 0.08-0.18) from the intense wildfires in the Iberian Peninsula. It was this unique loading of aerosol types, rarely observed in this combination and magnitude over the UK, that resulted in enhanced scattering of the short/medium visible wavelengths of incoming solar radiation, and it was this that led to the Sun and sky taking on such a dramatic appearance.

This work was supported by Droplet Measurement Technologies and Enviro Technology Services Ltd via loan of the MiniMPL-532-C elastic backscatter lidar system.

Is Anthropogenic Global Warming Accelerating?

Stuart Jenkins, PhD Researcher, AOPP, Dept. of Physics, University of Oxford

While successive IPCC reports have assessed the level of human-induced warming above preindustrial levels, none have yet systematically assessed the rate of anthropogenic warming. This is despite several studies highlighting the rate of warming as a key variable in climate change policymaking. The decadal trend in the global temperature anomaly likely increased in the 2010s, with warming having temporarily ‘paused’ through the 2000s. Here we show that an attribution using available radiative forcing (RF) data suggests a part of this warming acceleration is due to anthropogenic RF trend changes – aerosol RF reductions contribute to an overall anthropogenic RF trend increase (0.04 W/m2/yr in 2000-2010; 0.06 W/m2/yr in 2010-2020). The consequences of these assumed trends are a suggested increase in the anthropogenic warming rate of between 50 and 100% since the early 2000s. Here we assess the observational evidence behind the aerosol and anthropogenic RF accelerations using satellite observations of the Earth system since 2000. We conclude that while evidence exists that RF trends are responsible for global temperature trends over the previous two decades, downstream evidence is largely circumstantial with credible counterhypotheses including no change in the aerosol RF trend. Observed trends are significantly affected by processes driven by internal variability, precluding a more accurate assessment of externally forced behaviour over such short observational records.

Evaluation of UKESM1’s Sulphur Cycle

Dr Catherine Hardacre, Scientist, Met Office

UKESM1 is the latest generation Earth system model to be developed in the UK. It simulates the core physical and dynamical processes of land, atmosphere, ocean and sea ice systems which are extended to incorporate key marine and terrestrial biogeochemical cycles. These include the carbon and nitrogen cycles and interactive stratosphere-troposphere trace gas chemistry. Feedbacks between these components that have an important amplifying or dampening effect on the physical climate, and/or change themselves in response to changes in the physical climate are also included. One focus for the future development of UKESM1 is improved treatment of sulphur processes, including emission, chemical processing and deposition in the aerosol-chemistry scheme, UKCA-Mode. These processes span land-atmosphere and ocean-atmosphere boundaries and can therefore impact feedbacks between these systems. Emissions of SO2 can be oxidised to form sulphate aerosol, which plays a key role in acid deposition, atmospheric aerosol loading and cloud properties, thereby directly contributing to the Earth’s radiative balance. Good representation of sulphur processes in UKESM1 is therefore essential for constraining uncertainties associated with the impacts of aerosols on the Earth system and thus understanding the global climate. Here we evaluate biases in the model’s simulation of SO2 and sulphate by analysis of UKESM’s sulphur budget, comparison with observations from ground-based measurement networks and OMI, and assessing changes to UKESM1’s SO2 dry deposition parameterization. 

We find that UKESM1 broadly captures the spatial distribution of surface SO2 and sulphate as well as the historical trend for decreasing concentrations of both species over Europe and the USA for the period 1987 to 2014. However, in the polluted regions of the Eastern USA and Europe, UKESM1 over-predicts surface SO2 concentrations by a factor of 3.2-3.4 while under-predicting surface sulphate concentrations by 25-35%. In the cleaner Western USA, the model over-predicts both surface SO2 and sulphate concentrations by a factor of 12 and 1.5 respectively. Using a newly available data product for total column SO2 (TCSO2) from OMI we also find that UKESM1 over-predicts TCSO2 over large source regions including India, China, the USA and Europe.

We modify UKESM1’s SO2 dry deposition parameterization to simulate the process more realistically with the result that more SO2 is dry deposited to land and ocean surfaces. This reduces atmospheric SO2 and sulphate concentrations, and ultimately reduces cold bias in UKESM1's simulation of mid 20thC global mean surface temperatures. In comparison with the observations, we find that the changes reduce UKESM1's over prediction of surface SO2 concentrations and TCSO2. However, analysis of UKESM1’s global and regional sulphur budgets shows that model bias in SO2 and sulphate over the polluted regions is also driven by uncertainty in the model’s simulation of SO2 oxidation.


Urban Air Quality

Organic Emissions from Solid Fuel Combustion Sources in Delhi, India

Gareth Stewart, Support Engineer, FAAM

​Air pollution guidelines for tropospheric ozone and particulate matter are routinely exceeded in India, where around three quarters of a billion people use solid fuels as their principal energy source for cooking and heating. Despite this, very limited information is available on the composition and quantity of emissions of organic material from many common solid fuels. As part of the Atmospheric Pollution and Human Health in an Indian Megacity project, over 70 fuel samples of a range of fuel woods, cow dung cakes, crop residues and municipal solid waste were collected from across the state of Delhi. These fuel samples were then burnt under domestic stove conditions at the combustion facility at the National Physical Laboratory in Delhi and the organic emissions sampled using a range of techniques.

This talk will examine key research findings from several recent studies (Stewart et al., 2021a; Stewart et al., 2021b; Stewart et al., 2021c). Emission factors of over 190 volatile organic compounds (VOC) were measured using proton-transfer-reaction mass spectrometry, dual channel gas chromatography and two-dimensional gas chromatography. Semi-quantitative measurements of intermediate volatility and semi-volatile VOCs (C12 -Cx) were obtained by adsorbing the gases onto solid phase extraction disks. Particle samples were collected onto PTFE filters and analysed using two-dimensional gas chromatography coupled to time-of-flight mass spectrometry.

Model-ready organic emission profiles for domestic solid fuel combustion sources were developed and it was estimated that phenolics would contribute 10–70% of the secondary organic aerosol. Furanics were the most important reactive species, contributing 9–48% of the OH reactivity and 9–58% of the SOA. Different combustion sources were also compared, with emissions from fuel wood, crop residue, cow dung cake and municipal solid waste (MSW) burning shown to be 30, 90, 120 and 230 times more reactive with the OH radical than emissions from liquefied petroleum gas (LPG) fuel. This study also estimated 3–4 times more SOA from cow dung cake combustion and 6–7 more from MSW combustion than fuel wood under comparable combustion conditions.


A 1 km2 emission inventory for India was also developed which constrained the magnitude of VOC emissions over a 25-year period, using a range of detailed fuel usage inputs. This found that cow dung cake emissions were a disproportionally large contributor to NMVOC emissions from residential combustion and that emissions from agricultural crop residue burning on fields and municipal solid waste combustion were also significant VOC sources. 

Air Quality in Vietnam: Overview and Key Findings from the 2-Cities Project

Dr Grant Forster, NCAS Research Scientist, School of Environmental Sciences, University of East Anglia

​Vietnam is one of the fastest growing economies in SE Asia and has undergone rapid urbanisation, industrialisation and population growth. This has led to the deterioration of, amongst other factors, air quality, with Vietnam being one of the most polluted countries in the world, ranked 170th out of 180 countries for air quality in a recent survey. Air quality monitoring in Vietnam is patchy and previously reported studies are often quite limited or dated. Given the rapid economic development and the growth of cities such as Ho Chi Minh City and Hanoi, there is a pressing need for new, up-to-date air quality measurements and a reassessment of the major sources of the observed pollution and its implications for human health. We will present an overview and the key findings from recent field campaigns in Ho Chi Minh City (11°N) and Hanoi (21°N), the two largest cities in Vietnam. Measurements were made of a wide range of air quality indicators in both the gas (O3, NOx, CO, SO2, VOCs, OVOCs, GHGs) and particulate phases (PM2.5, trace metals, major ions, organic speciation), using both traditional and low-cost sensor technologies.

In Situ Ozone Production is Highly Sensitive to Volatile Organic Compounds in the Indian Megacity of Delhi

Beth Nelson, PhD Student, University of York

Delhi suffers from some of the poorest air quality in the world. While ambient NO2 and particulate matter (PM) concentrations have received considerable attention, ozone (O3) levels are often ignored. High levels of O3 can adversely affect human health, leading to respiratory problems. With recent studies suggesting a reduction in PM in China is leading to increased surface-level O3 production(1), it is important to assess the chemical processes in Delhi’s atmosphere. To identify the main chemical drivers of O3 production, a detailed analysis of its photochemical precursor species is required.

During October 2018, concentrations of a large range of speciated volatile organic compounds (VOCs), oxygenated VOCs (o-VOCs), NOx, HONO, CO, O3, and spectral radiometry, were continuously measured at an urban site in Old Delhi. Throughout the campaign, O3 concentrations breached the recommended WHO 8-hour exposure limit of 50 ppbv on several occasions, with daily peaks regularly exceeding 100 ppbv. Observations also reveal very high concentrations of aromatic compounds, known to play an important role in in-situ O3 formation, with total BTEX (benzene, toluene, ethylbenzene, xylenes) exceeding 150 ppbv.

The sensitivity of O3 formation to changes in VOC and NOx concentrations, photolysis rates and HO2 radical uptake to PM, is explored using an observationally constrained photochemical box model, incorporating the Master Chemical Mechanism (MCMv3.3.1, mcm.york.ac.uk) into the AtChem2 modelling toolkit(2). The model was constrained to measurements of 85 VOCs, NO, CO, HONO, 34 photolysis rates, aerosol surface area, and meteorological observations.

This work probes the chemical processes that drive in-situ O3 production in Delhi’s atmosphere. The sensitivity of O3 production to different classes of VOCs is explored, in order to aid the development of pollution control strategies. 

1.            K. Li et al., PNAS, 2018, 116 (2), 422-427
2.            R. Sommariva et al., Geosci. Model Dev., 2020, 13, 169-183


Observations of Volatile Organic Compounds in Vietnamese Cities

Jim Hopkins, Experimental Officer, NCAS, WACL, University of York

Vietnam is thought to be one of the most polluted countries in the world.  It is situated in a region of extensive biodiversity, rapid population growth and has an economy heavily reliant on agriculture, all of which impact, or are impacted by, increasing levels of air pollution.  A project was undertaken in 2018-2019 to better understand the atmospheric composition within two of Vietnam’s largest and most populated cities: Ho Chi Minh City (HCMC); and Hanoi.  Hanoi is located in the North of Vietnam and at times experiences outflow from China, while HCMC sits in the South and is generally influenced by greater solar radiation and warmer temperatures.  We pay particular attention to the VOC composition, taking advantage of the broad range of speciated VOCs observed during the campaigns.  Traffic sources were found to be a major contributing factor to VOC levels in both locations, but differing meteorological conditions encountered during the study led to large differences in both their abundance and behaviour.  Oxygenated compounds and alkanes, were found to dominate the VOC composition in both cities (accounting for around two thirds of the total measured mass of VOC), whereas aromatics and unsaturated VOCs were found to be the main contributors to ozone formation due to their generally shorter atmospheric lifetimes.  We will discuss the observations in the context of other recent field deployments in other megacities namely Delhi, Beijing and London.

Source Apportionment of Particulate Matter using One Year of Hourly Trace Metal Data at an Urban Background Site in London

Anja H. Tremper, Research Fellow, Imperial College London


Exposure to PM2.5 (particles < 2.5 μm in diameter) is the fifth leading risk factor for death in the world and the adverse effects are well known (Cohen et al. 2017); this is especially true for urban environments. Sources need to be accurately identified and quantified to understand their contribution to PM10 and PM2.5 exposures, to evaluate their seasonality and changes in emission strength in the short term and any policy intervention in the longer term. High time resolution measurements of PM composition, such as those from the Xact instrument allow for a more accurate identification and quantification of sources as the high time resolution reflects short term changes due to emission and atmospheric processing. Many studies have examined high time resolved data from short campaigns. Here we present positive matrix factorisation (PMF) analysis of 12 months data from an urban background location in London, UK.


Hourly PM10 measurements of a range of elements were made with the Xact 625i at an urban background location in south London (51.45N, 0.04W) between Aug. 2019 and Aug. 2020. Source contributions were determined with PMF using the Source Finder software (SoFi) (Canonaco et al., 2013). To identify known periods of fireworks displays which are common in the UK around 5th Nov., PMF was carried out in three steps: i) initially factor profiles were established excluding the fireworks periods (2-12 factors tested); ii) established profiles (bootstrap (BS) mean of 9 factor profiles) were constrained, and additional unconstrained factors were included for the fireworks period to identify fireworks factors; iii) the full period was run with all identified profiles; BS was performed.

Black carbon, PM10, PM2.5 mass concentrations and NOx were used to verify source attribution.


Ten factors were identified, the chemical composition of profiles and their diurnal patterns are shown. Two traffic sources were identified, one associated with brake and the other with tire emissions. Two combustion sources (combustion/Pb and biomass/solid fuel combustion) were identified with a distinctive increase in concentration in the evenings. Two soil factors with crustal elements in their composition were detected with one dominated by Ca and the other by Si; these were thought to be caused by building works and soil resuspension, respectively.

Further, an oil source associated with Ni and V and sea salt were detected. A source dominated by sulphur, with no discernible diurnal pattern represented secondary inorganic aerosol. One fireworks factor was identified, with a clear peak in the evening but with concentrations staying elevated throughout the night during late October/early November due to Diwali and Guy Fawkes celebrations.

Figure 2: Diurnal pattern of sources

In a next step the source identification will be supplemented by inorganic and organic data from the ACSM instrument.

This work was supported by the Natural Environment Research Council (NERC) under grant NE/T001909/2.


Tropical Cyclones

Relationships Between Equatorial Waves and TC Activity in the West Pacific

Xiangbo Feng, Research Scientist, NCAS

​Convectively coupled equatorial waves at synoptic scales can potentially act as tropical cyclone (TC) precursors. Here, we will present the process-based causal relationships between westward-moving equatorial waves and TCs in the West Pacific, and depict the underpinning mechanisms, including the modulation by ENSO. The evaluation is based on ERA5 reanalysis. Instead of traditional equatorial wave data, we use the dynamical fields of equatorial waves identified by projecting horizontal winds and geopotential height onto horizontal structures of theoretical equatorial wave modes. One advantage of our wave data is that we can examine divergence/vorticity of waves at various vertical levels, which is critical to understanding the TC-wave relationship. The ERA5 TC-wave relationship can be used as a benchmark to evaluate the representation of the relationship in GCMs, to inform the possible causes of TC frequency bias.

Increasing Tropical Cyclone Intensity and Potential Intensity in the Subtropical Atlantic around Bermuda from an Ocean Heat Content Perspective 1955 - 2019

Samantha Hallam, Post-Doctoral Researcher, Irish Climate Analysis Research Unit, Maynooth University, Ireland

Tropical cyclone (TC) activity and intensity within a 100km radius of Bermuda is investigated between 1955 and 2019. The results show a more easterly genesis over time and significant increasing trends in tropical cyclone intensity (maximum wind speed (Vmax)) with a decadal Vmax median value increase of 30kts from 33 to 63kts (r=0.94, p=0.02), together with significant increasing August, September, October (ASO) sea surface temperature (SST) of 1.1°C (0.17 °C per decade) r= 0.4 (p<0.01) and increasing average ocean temperature between 0.5–0.7°C (0.08-0.1°C per decade) r=0.3 (p<0.01) in the depth range 0-300m. The strongest correlation is found between TC intensity and ocean temperature averaged through the top 50m ocean layer () r=0.37 (p<0.01).

Using the Hydrostation S timeseries, this study shows how tropical cyclone potential intensity estimates are closer to actual intensity by using  as opposed to SST. The widely used sea surface temperature potential intensity index is modified by using to provide a closer estimate of the observed minimum sea level pressure (MSLP), and associated Vmax than by using SST, creating a potential intensity (_PI) index. The average MSLP difference is reduced by 12mb and proportional (r=0.74, p<0.01) to the SST- temperature difference. The results suggest that the index could be used over a wider area of the subtropical/tropical Atlantic where there is a shallow mixed layer depth.

The Impact of Tropical Cyclones on Potential Offshore Wind Farms in Mexico

Dr Oscar Martinez-Alvarado, Research Scientist, NCAS, University of Reading

The climate crisis has led to an increased interest in renewable energy sources, particularly in regions which have excellent wind energy potential, but at present a limited installed capacity, such as Mexico. The world’s tendency is to install wind power in offshore facilities. However, due to Mexico’s tropical geography, wind farms would be at risk of potential damage from strong winds associated with passing tropical cyclones. This study investigates the impacts that winds associated with tropical cyclones would have on potential offshore wind farm sites. The ERA5 reanalysis has been used to identify two sites in the Pacific coast and two in the Gulf of Mexico with high wind power capacity factor potential in Mexico. The potential effects of four major hurricanes on hypothetical offshore wind farms at these locations has been investigated. Furthermore, a tropical cyclone best-track dataset (from 1979-2019) was used to put the case study results into a climatological context and investigate the potential return periods of damaging winds from tropical cyclones in each region. The results show the sites on the Pacific coast to be optimal locations for the construction of offshore wind farms. The return period for tropical cyclones with near-surface winds exceeding 50 m/s has been estimated above 64 years, while the mean capacity factor during hurricane season (1 June - 30 November) in these regions was found to be around 20% or above. The sites in the Gulf of Mexico are more susceptible to the damaging winds associated with TCs but do present a viable capacity factor as well. The implications of this study for offshore wind farm planning in the country and in the tropics in general will be discussed.

Analysis of Tropical Low Pressure Systems that Made Landfall in Mozambique Between 1960 and 2020: Their Total Number and Respective Affected Areas

Hélio Vasco Nganhane, Teacher, Pungue University, Mozambique

This study investigates the total number of tropical low pressure systems that made landfall in Mozambique in the last 60 years, and the respective affected areas. By analyzing the IBTrACS (International Best Archives for Climate Stewardship) data set, it was possible to discover that there are a total number of (45) tropical low pressure systems that made landfall  in Mozambique in the last 60 years. Most of the systems originated in the Mozambique Channel and Southwest of Diego Garcia. Considering, the phase of each system at the time of landfall or the phase of each system on its arrival in Mozambique, in general between 1960-2020, they made landfall in Mozambique, (10) Tropical Disturbances, (12) Tropical Depressions; (8) Moderate Tropical Storms, (6) Strong Tropical Storms; (4) Tropical Cyclones and (5)  Intense Tropical Cyclones. The coast with the largest number of landfall is northeast with 44.4% followed by the east coast with 28.8% and southeast with 26.6%, at least each coast has already been hit by an intense tropical cyclone (Tropical Cyclone of Category 4). The province with the highest number of landfall is  Zambézia and the most affected district by landfall is Pebane. The Zambézia province is followed by the  Inhambane province, the most affected districts by landfall are Vilankulo and Massinga. After Inhambane follow the provinces of Sofala and Nampula. In Sofala province, the district with the highest number of landfall is Buzi and in Nampula province is Moma. The province without any record of tropical low pressure systems landfall is Tete.

Tropical Cyclones in Future HighResMIP Experiments : Explaining and Reconciling Projections

Benoît Vannière, Research Scientist, NCAS, University of Reading

Although most GCMs project a decline of tropical cyclone activity in a warmer world, some recent studies have cast doubts on this consensus by suggesting that the number of tropical cyclones might increase in future.  The HighResMIP experiments offer such an example of contradicting projections. Indeed, AMIP-type experiments which have been forced by transient SSTs preserving the trend simulated by CMIP6 models in scenario SSP585, predict an increase of cyclone activity in the North Atlantic, whereas experiments with the same atmospheric models coupled to an ocean model predict a decline. In this paper, we intend to explain and reconcile those results. To do so, we compare several recent and past projects including HighResMIP, CMIP6 scenario SSP585 and the time-slice experiments of the UPSCALE project. We used several different approaches to explain the future change in TC activity, including SST anomalies relative to the tropical mean, the ventilation index for tropical cyclone genesis and predictors of tropical cyclone precursors.

SST anomalies show that subtle differences in SST trends between basins in the AMIP and coupled experiments can explain the differences in TC projections. This analysis should guide the construction of SST for the transient AMIP experiments used in future HighResMIP protocols. Once the less reliable projections have been discarded from our model ensemble, we show that there exists a remarkable agreement between the projections of HighResMIP coupled, scenario SSP585 and UPSCALE. We find that the saturation deficit is the component of the ventilation index which explains the largest fraction of the change, with the potential intensity and vertical wind shear playing a secondary role. Finally, we find that there is some agreement between models on the different time of emergence of a trend in TC activity in each basin, which we attempt to link to differences in the time of emergence of the trend of saturation deficit.

The Reason for the Observed Increase in Hurricane and Named Storm Activity

Conor McMenemie, Lead Researcher, NiCE Research

It is known that sea surface temperatures (SSTs) are a key component for energising equatorial Atlantic storms into Named
Storms and Hurricanes. That the SSTs in the region which germinate such events are largely dependent upon the duopoly of the surface temperature of the ocean currents flowing towards the equatorial Atlantic, and the heating effect applied by the sun. With reference to the relevant ocean currents plus scrutiny of rainfall and river flow data upwind across the Sahelian region of Sub Saharan Africa, it can be established that there has been a
significant loss of cloud cover. This has allowed for a corresponding increase in isolation, resulting in the increased SSTs which gives rise to the increased Storm and Hurricanes. Further rendering of the data highlights the cause of these events as a reduction in the frequency of the African Easterly Wave (AEW) weather system. This has allowed for an additional multi hundred terrawatt ocean heating effect, which is providing the additional 'fuel' for the storms and hurricanes. Although it had been suggested that this is merely a regional effect, a trinity of factors has ensured that the AEW frequency factor has a notable impact on a number of other large scale climatic events due to:
[1] The ability for the prevailing winds to transport any variability in cloud cover, or the conditions which promote cloud formation, westwards across the Equatorial Atlantic basin into the Pacific, producing an additional ocean heatings effect there.
[2] That the normal ocean currents carry the additional absorbed solar heat northwards and southwards towards the poles.
[3] That some of this additional heat which dissipates from the oceans into the atmosphere, is carried by wind driven air currents onto the continents, where it contributes to an observed increase in mean temperatures there.
The factors affecting the original precursors to the AEW system can be backtracked to the Ethiopian Highlands, where the confluence of a number of atmospheric events had given rise to this AEW climatic chain reaction. It will be demonstrated here that human activity had unintentionally made sufficient alterations to one of these precursors, in an area of uncommon meteorological vulnerability during the hurricane season. That as a consequence we had inadvertently degraded one of the planet's major weather systems, which after being allowed to go unnoticed since the start of the last
century. That this is the principal reason for the observed increase in Atlantic Hurricane and Named Storm activity.


Atmospheric Composition: Ozone and Methane

Monthly Estimation of Ozone Monitoring Instrument-Aerosol Index (OMI-AI) from Meteorological Data in Southern Nigeria

Mukhtar Abubakar Balarabe, Lecturer, Department of Physics, Umaru Musa Yar`adua University, Katsina. Katsina state, Nigeria

The objective of this work is to estimate the monthly mean Ozone monitoring aerosol index (OMI-AI) using the available ground observation meteorological data in southern Nigeria. Ten years (2010-2020) of AI data downloaded from the OMI website and the meteorological data (visibility, temperature, wind speed, Sea level pressure, and relative humidity) obtain from National Oceanic Atmospheric Administration-National Climate Data Centre (NOAA-NCDC) was used. The model coefficients were determined and applied to another dataset for cross-validation. The model accuracy was determined using the weighted mean absolute percentage error (wMAPE), coefficient of determination R2, and the root mean square error (RMSE) calculated at the 95% confidence level. The results showed a high level of accuracy between November to March of every year explaining about 85% of AI variability. It however decreases from April to October (wMAPE 10%; R2 0.72. RMSE 0.07) in April. The lowest accuracy was observed in August which explains the influence of the rainy season on dust accumulation in the atmosphere during the period. It is also concluded that the accuracy of these models is seasonal dependent. Very high during the dust transport period, (November-March) and low during the rainy season (April to October).

An Assessment of the Airborne Performance of Two UV Ozone Photometers Onboard the FAAM Airborne Laboratory

Jake Vallow, Assistant Core Chemistry Technician at the FAAM Airborne Laboratory, NCAS

​We provide a comprehensive assessment of the performance for a 2B Technologies 205 and ThermoScientific 49i UV ozone photometers during their operation on the FAAM Airborne Laboratory. To achieve this, data from the ARNA (Atmospheric Reactive Nitrogen cycling over the Atlantic Ocean) airborne campaigns in 2019 and 2020 at the Cape Verde Atmospheric Observatory, in conjunction with other test flights and laboratory experiments, have been used to compare airborne and ground based ozone observations. We investigate potential sources of systematic errors and, where appropriate, make recommendations of how to mitigate these biases or account for them in the overall measurement uncertainty.

Sensitivity of Ozone Production in the UK to VOC and NOx Levels

Michael Sanderson, Senior Scientist, Met Office

In this study, we examine the impact of NOx and VOC emissions reductions on ozone levels over the UK. Two methods were tested for identifying regions in the UK where ozone production is either NOx or VOC limited, which were based on chemical indicators and ozone isopleths. The indicators showed there were areas where ozone production was limited by either VOC or NOx levels on several days during August 2020 when high ozone levels were observed. However, the ozone isopleths were harder to interpret, and suggested that NOx was in excess most of the time, meaning ozone levels were predominantly VOC limited.

Identifying Sources for Methane Mitigation using Mobile Atmospheric Greenhouse Gas Flux and Isotope Measurements

Dr Rebecca Fisher, Lecturer, Department of Earth Sciences, Royal Holloway University of London

Global averaged methane mole fraction continues to increase each year. Although over the last three decades methane emissions in the UK have decreased, the national atmospheric emissions inventories for 2016-2018 showed a plateau. Further methane emission reduction is urgent and essential to meet Paris Agreement and net zero targets. Using vehicle mounted high precision atmospheric methane analysers we use atmospheric measurements to locate and quantify methane emissions from individual sources. Methane isotopic measurements or methane:ethane ratios are used to identify the source type. Over the last eight years Royal Holloway have carried out mobile campaigns across the UK to measure emissions from gas distribution, waste treatment (landfill and biogas plants) and agriculture. Recent surveys carried out as part of UN-CCAC funded methane science studies have mapped methane leaks (which are predominantly from leaks in the gas distribution network) in London and Birmingham.

Here we describe Royal Holloway’s new vehicle mounted measurement system (MIGGAS, Mobile Integrated Greenhouse Gas Flux and Isotope Analysis System) which has been set up in a hybrid car. A cavity ringdown spectrometer making 10 Hz measurements of methane and carbon dioxide mole fraction is coupled to a sonic anemometer for improved flux measurements. Real time source-type identification is achieved using isotope and ethane:methane ratio measurement.


As well as helping to locate the methane sources that can be more easily removed, using atmospheric measurements to quantify emissions changes will be an important check on the effect of reduction efforts as we work towards meeting net zero targets.

Tropospheric Ozone in the North Atlantic: Comparison of UM-UKCA and Remote Sensing Observations for 2005-2018

Dr Maria Russo, Research Associate, NCAS, University of Cambridge

Tropospheric ozone is an important component of the Earth system. It is a greenhouse gas and an oxidant and can therefore affect climate directly, through its radiative impact, and indirectly, through the oxidation of aerosol precursors and its impact on OH and methane. This work aims to investigate tropospheric ozone changes across the North Atlantic and how it varies in the vertical. Model integrations and observations from satellite retrievals are used to investigate the seasonal and decadal variability of ozone in the North Atlantic. We further analyse possible reasons for discrepancy between modelled and observed tropospheric ozone.

Understanding Formaldehyde and Glyoxal for New Satellite Measurements

Mark Blitz, Research Scientist, NCAS

Satellite measurements of pollutants such as O3, NO2, formaldehyde (FA, HCHO) have enabled significant advances in our understanding of pollutant emissions and atmospheric chemistry. However, with the exception of methane, VOC emissions cannot be detected from satellites but the oxidation products FA and glyoxal (GL, HC(O)CH(O)) can be observed. New satellite launches will provide a step-change in the quality of spatial and temporal data on these compounds allowing resolution within cities.

The ratio of glyoxal to formaldehyde (RGF) varies with the type of VOC (e.g. GL yield from aromatic oxidation is much higher than alkanes) and therefore measurements of RGF potentially allow the determination of the composition of the primary emissions. The GL yield from VOC oxidation is the major determinant of RGF. The end goal is to answer the research question: can RGF from satellite measurements be used to understand primary emissions and validate emission inventories?

The major thrust of this work is to determine the oxidation chemistry of a range of VOC - associated with anthropogenic and biomass burning emissions - to form FA and GL. The initial work has been with acetylene and glycolaldehyde as these can oxidize to GL without NOx. Further work will focus on aromatics which require NOx to form GL.


Boundary Layer and Turbulence

LES Simulations to Model the Air Flow Regimes in Urban Canyon using OpenFoam

Peri Subrahmanya Hari Prasad, PhD (pursuing), Dept of CORAL, IIT Kharagpur, Kharagpur, India

In the New era of science and technology, the analysis on canyon flows are significantly increasing. So the basic flow regimes of canyons are found out using LES simulations in OpenFoam. The basic distance between canyons required to change the airflow regimes are analyzed. Characteristic canyon geometries, expressed in terms of height-to-width (H/W) and length-to-height (L/H) ratios are found out. The results are compared with RANs models in the literature.

Variability in the Short-Range Dispersion of Passive, Short-Duration Emissions

Dr Paul Hayden, EnFlo Lab Manger and AMOF Instrument Scientist, University of Surrey

The objective of this analysis was to use short duration wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source (320mm) in a deep turbulent boundary layer (~1m) and to develop scaling rules that reduce the results to a universal form. The experiments were carried out in a 1 m deep simulated atmospheric boundary layer in the EnFlo meteorological wind tunnel at the University of Surrey. Ensembles of between 100 and 200 repeat emissions were used, with emission durations between 0.067 and 1.02 s with the reference flow speed at the boundary edge of 2 ms-1. The structure of the evolving clouds was analysed to determine time of flight, along-wind spread and dose and to compare the dose behaviour with the concentration field in a plume (continuous release) from the same source.

Using Series Basis Functions with the Complex Variable Boundary Element Method

Bryce D. Wilkins, Graduate Student, Carnegie Mellon University

The Complex Variable Boundary Element Method (CVBEM) is a numerical tool for modelling potential problems with applications in fluid dynamics and diffusion, among other areas of interest in atmospheric science. The CVBEM develops an approximation function that is a linear combination of analytic complex variable functions. Recent research has been directed towards identifying highly effective basis functions for use in the linear combination, as well as developing algorithmic techniques for improving the efficiency of the employed basis functions. In this talk, we will examine the latest effort with regard to basis function development, which incorporates the use of partial sums of series-type basis functions that are expanded about various points in the exterior of the problem region. The talk will discuss the implementation and effectiveness of these basis functions and results will be shown for a benchmark boundary value problem with Dirichlet and Neumann boundary conditions.

An Evaluation of the 2020 Upgrades to the NCAS-AMOF Boundary Layer Mobile UHF Radar Wind Profiler

Dr Emily Grace Norton, AMOF Instrument Scientist, AMOF-NCAS University of Manchester

The NCAS-AMOF boundary layer mobile UHF Radar wind profiler (RWP) has been operating fairly continuously since 2002 both on campaign or at one of its long term measurement sites based in Cardington or Capel Dewi. In more recent years there have been some problems with the controlling computer so Degreane Horizon were commissioned to undertake an upgrade to the electronics.

The upgrade consists of  a new controller computer with an upto date compact FPGA card that can support real-time digital signal processing (DSP) and it also has a bigger dynamical range.

This has an advantage of enabling more profiles to be measured in a given time which improves the signal to noise ratio and the range of the usable wind measurements.

This piece of work evaluates the improvements to the RWP measurements since the upgrade and continues the work on comparisons between UHF and VHF radars.

Modelling Chemistry and Transport in Urban Street Canyons: Comparing Offline Multi-Box Models with Large-Eddy Simulation
Yuqing Dai, PhD Student, University of Birmingham

We propose a flexible multi-box model that can be used to simulate the emission, advection, diffusion, and transformation of chemical species, and deposition in street canyons with any aspect ratio (AR, i.e., the ratio of the canyon height to the street width) for which a prior LES simulation of the flow exists. The multi-box model formulation permits spatial disaggregation of emission sources and deposition sinks, as is commonly observed in real streets. The performance of the multi-box models is compared with the benchmark published LES data, including chemistry, for the regular (AR = 1) and deep (AR = 2) canyons. The multi-box model captures well the flow characteristics in street canyons at about 4% of the LES computational cost. The spatial patterns of reactive species are in good agreement with those from the LES, especially for the deep canyon from which air escapes more slowly. The multi-box model offers the advantage of fast computation, consistent accuracy, and adequate spatial representation of air pollution inside street canyons, and it is a computationally cost-effective approach to investigate fast non-linear chemistry or microphysics at the street scale.

The Reason I Am Switching from Vector to Scalar Averaging for Surface Wind Data

David Hooper, NCAS Instrument Scientist, NCAS

​For smoothing surface wind data, I have always considered vector averaging (i.e. applied to eastward and northward components) to be more appropriate than scalar averaging (i.e. applied to speed and direction). Differences between the two methods are typically small. However, as a result of analysing almost 20 years of data from the NCAS Capel Dewi Atmospheric Observatory, I have found that they can be large when there is a large step change in direction or when the direction shows large fluctuations over a sustained period. Scalar averaging gives a better representation of the strength of the wind under such circumstances.

Stratospheric Processes 2

A Minimal Model for Predictability from the Stratosphere

Prof Andrew Charlton-Perez, Prof. of Meteorology, University of Reading

On sub-seasonal timescales, the stratosphere is a key source of prediction skill for the North Atlantic. A number of recent papers have recently shown substantial increases in correlation skill for forecasts initialised during periods in which the polar vortex is weaker or stronger than normal. In this talk, we will propose a minimal statistical model which can be used to understand this effect. The model can also be used as a useful baseline for discussing state dependent skill from the stratosphere and the windows of opportunity for sub-seasonal prediction.


Interactions Between the Stratospheric Polar Vortex and Atlantic Meridional Overturning Circulation On Multiple Timescales

Oscar Dimdore-Miles, PhD Student, University of Oxford

Variations in the strength of the NH winter polar vortex can influence surface variability in the Atlantic sector. Disruptions of the vortex, sudden stratospheric warmings (SSWs) are associated with an equatorward shift and deceleration of the North Atlantic jet stream, negative phases of the North Atlantic Oscillation as well as cold snaps over Eurasia and North America. Despite clear influence at the surface on sub-seasonal timescales, how vortex variability interacts with ocean circulation on decadal to multi-decadal timescales is less well understood. In this study we use a 1000 year pi-control of the UK Earth System Model to study such interactions using a wavelet analysis technique to examine not stationary periodic signals in the vortex and ocean. We find that intervals which exhibit persistent, anomalous vortex behaviour lead to oscillatory responses in the Atlantic Meridional Overturning Circulation (AMOC). The origin of these responses appears to be highly non-stationary spectral power in the vortex and the AMOC at periods of 30 and 50 years as well as feedbacks with the stratospheric influence over the NAO. On longer timescales (near 90 year periods) the signals in the AMOC influence the vortex through a pathway involving the equatorial Pacific and Quasi-biennial Oscillation. Using the relationship between persistent vortex behaviour and the AMOC established in the model, we also estimate the contribution of the 8 year SSW hiatus interval in the 1990s to the recent negative trend in AMOC observations. Using a regression analysis, we estimate that approximately 10% of such a trend may be attributed to the hiatus. These results represent a novel interaction between the stratosphere and ocean and stress the importance of considering non-stationarity when analysing variability in long GCM integrations. They also shed light on the possible role stratospheric signals have played in forcing the AMOC over the past decade which is key to understanding anthropogenic impacts on this circulation.

Regime Behavior in the Upper Stratosphere as a Precursor of Stratosphere-Troposphere Coupling in the Northern Winter

Dr Hua Lu, Research Scientist, British Antarctic Survey

The impact of stratospheric variability on the dynamical coupling between the stratosphere and the troposphere is explored regarding the role of the upper stratosphere. A new regime index is constructed to capture the seasonal development of the stratospheric polar vortex in the northern winter, based on the standard deviation of Ertel’s potential vorticity in the upper stratosphere in November-December. The narrow-jet flow regime is characterized by a polar vortex that is more confined to high latitudes in the early winter upper stratosphere. This upper-level vortex configuration is more susceptible to the disturbances of upward propagating planetary-scale Rossby waves; the stratospheric polar vortex thus weakens earlier and is vertically shallower. The wide-jet flow regime is characterized by a broader-than-average polar vortex that extends further into the subtropics in the early-winter upper stratosphere. The polar night jet then gradually strengthens, moves poleward and penetrates deep into the lowermost stratosphere, with a sharply-defined polar vortex edge accompanied due to more frequent Rossby wave breaking.

Composite differences between the wide and narrow jet regimes, defined in early winter in the uppermost stratosphere, are found to lead to lower-stratospheric and the tropospheric responses by one to two months, offering the potential for predictability of sub-seasonal to seasonal forecasts. The lower tropospheric responses in January-February are zonally asymmetric. The narrow-jet regime projects most strongly over the North Atlantic, with an equatorward-shifted, and/or broader westerly jet there. The wide-jet-regime response is characterized by a weakened westerly jet over the North Pacific. The two flow regimes also differ in their impacts on the storm track over Western Europe and the east coast of America, which may have implications for extreme weather events in those regions.

Stratospheric Response to Natural Forcings and Varying Tropospheric Aerosol Levels

Dr Beatriz Monge-Sanz, Research Scientist, NCAS and University of Oxford 

While the tropospheric response to different levels of tropospheric aerosols has been widely investigated, the stratospheric response is less well studied. We have used data from the SMURPHS model ensemble, a set of historical coupled atmosphere-ocean simulations performed with the HadGEM3 GC3.1 climate model version (Dittus et al., 2020). This ensemble consists of five sets of 5-member simulations, each set with a different scaling for anthropogenic aerosols, which has allowed us to assess the links between the stratospheric signal and the different tropospheric aerosol distributions.  

In this study we assess the stratospheric response to several natural and anthropogenic forcings. Our method allows us to quantify the response to solar, ENSO and volcanic signals, as well as to GHGs and tropospheric aerosols. Our results will show the stratospheric signal behaviour during the period 1900-present and links with associated surface features over the North Atlantic Sector.   

Arctic Ozone Depletion in 2019/20: Roles of Chemistry, Dynamics and the Montreal Protocol

Dr Wuhu Feng, NCAS Scientist, NCAS, University of Leeds

We use a three‐dimensional chemical transport model and satellite observations to investigate Arctic ozone depletion in winter/spring 2019/20 and compare with earlier years. We also use the model to distinguish between the roles of chemistry and transport in causing the low ozone values. Persistently, low temperatures caused extensive chlorine activation through to March. We have shown that by many metrics the Arctic winter/spring 2019/20 exhibited extreme behaviour within the record of the past two decades. March‐mean polar‐cap‐mean modeled chemical column ozone loss reached 78 DU (local maximum loss of ∼108 DU in the vortex), similar to that in 2011. A model simulation with peak observed stratospheric total chlorine and bromine loading (from the mid-1990s) shows that gradual recovery of the ozone layer over the past two decades ameliorated the polar cap ozone depletion in March 2020 by ~20 DU.


Risks and Hazards

Calculating and Communicating Ensemble-Based Volcanic Ash Risk for Aviation

Dr Natalie Harvey, Research Scientist, University of Reading

During volcanic eruptions Volcanic Ash Advisory Centers (VAAC) produce forecasts of ash location and concentration. However, these forecasts are deterministic and do not take into account the inherent uncertainty in the forecasts due to incomplete knowledge of the volcano’s eruption characteristics and imperfect representation of atmospheric processes in numerical models. This means flight operators have incomplete information regarding the risk of flying following an eruption. There is a need for a new generation of volcanic ash hazard charts allowing end users to make fast and robust decisions using risk estimates based on state-of-the-art probabilistic forecast methods.

In this presentation, a method for visualizing ash concentration forecasts using a risk-matrix approach will be applied to the 2019 eruption of Raikoke 2019. These risk-matrix graphics reduce the ensemble information into an easy-to-use decision-making tool. In this work the risk level is determined by combining the concentration and dosage of volcanic ash and the likelihood of that concentration occurring. Here the visualisation technique is applied to both an a priori 1000 member ensemble with perturbed eruption source parameters and internal simulator parameters and a posterior ensemble, also with a 1000 members, with parameters perturbed using ranges refined by matching the a prior ensemble to HIMAWARI satellite retrievals of ash column loading. The overall area of risk is reduced by over 60% when using the posterior ensemble at a lead time of 48 hours. This demonstrates the impact of using satellite observations to constrain the forecast uncertainty and their potential to reduce the disruption to airline operations.  This approach could be extended to include other aviation hazards, such as desert dust, aircraft icing and clear air turbulence.

Rainfall Rescue: Improving Understanding of UK Rainfall Related Risks with Citizen Scientist Volunteers

Prof Ed Hawkins, NCAS, University of Reading

​The UK has some of the longest weather records anywhere in the world, but there are still enormous quantities of historical observations inaccessible to climate science. Hundreds of millions of weather measurements are still only available in the original hand-written copies stored in various archives. The ‘rescue’ of this data is a significant undertaking but would add far more detail to our understanding of past variations in weather and inform our knowledge of climate-related risks. This talk describes the RainfallRescue.org initiative, which took a ‘citizen science’ approach to rescue over 5 million rainfall observations taken all over the UK in the period before 1960. More than 16,000 volunteers contributed during the first UK COVID-19 lockdown, and their efforts have more than doubled the total number of monthly rainfall observations available in the UK digital database. This will enable the detailed gridded records of UK rainfall to be extended backwards in time to the early 1800s, a period which includes a number of interesting wet and dry periods which were previously poorly quantified.

Plastics in the Atmosphere – Lessons from Public Health and Covid-19 on the Perception and Communication of Risk

Prof Mary E Black, Non Executive Director, NCAS and St Andrews University

​Plastics are materials that have been mass-produced in rapidly escalating amounts since the 1950s. Microplastics (defined as smaller than 5 mm in size) are now widespread across the natural world and in living organisms.

Many atmospheric scientists don't necessarily refer to airborne particles that have plastic properties at 'microplastics'. It is a somewhat emotive term, indeed some materials described as microplastic are not actually plastic at all, at least from a purely technical definition. [A plastic is technically an organic polymer that can be moulded into shape while soft; many polymeric organic chemicals exist in aerosol entirely naturally but were never mouldable.] The term microplastic conjures images of tiny fragments of degraded plastic bag, but in the context of air pollution could equally mean a fragment of road surface, piece of worn tyre, or fragment of brake material.

In most air quality circles polymeric particles released from tyre, brake and road surface wear fall within the classification of Non-Exhaust Emissions, (NEE) - and they are very important indeed because NEE are a source of damaging urban particulate matter that will remain even when the transport fleet is decarbonised. What is and isn’t a microplastic may sound like a discussion of semantics, but it is important because there is a critical need to distinguish between what are tiny breakdown products from the slow degradation of waste (e.g. plastic bags fragmenting in the ocean) and what are primary, directly emitted particles from man-made processes particularly those made by high energy friction.

The understanding of how plastic particles interact in other parts of the biosphere is growing. We can detect plastic particles in human and animal tissues, and small particles of plastic can leach biologically active ingredients that can potentially affect biological processes including reproduction, development of cancerous cells.  Airborne microplastics are therefore likely bad for health when inhaled. But so are virtually all particles. Every day we inhale some extremely toxic materials, notable chemicals like transition metals and polycyclic aromatic compounds, but few understand where they come from or even what they are. On the basis of what we breathe in each day, microplastics make up only a tiny fraction of either mass or health risk. Giving a particle an emotive description with strong public resonance potentially distorts both research and the policy response.  When risk is not placed in context, poor decision-making can be a consequence.


One method of spread of microplastic particles is atmospheric transport arising from sources on land and from the ocean. We are making good progress in tracking the distribution of microplastics and have indications that their ingestion, particular via food, but also potentially air, are harmful to human health. Reporting of microplastic air pollution has a considerable media profile just now. Plastic waste has exceptional media visibility, the blue planet effect. The translation of that genuinely huge environmental problem into the atmospheric space then gets amplified further because inhaling ‘microplastics’ sounds absolutely terrible.

There is much still to discover about the formation, transport and wider impacts of microplastics in the environment, including those that are airborne. Evidence around either human or ecosystem toxicity is likely to further emerge but setting what we know in context with other human exposures, and particle toxicities will be critical in defining a proportionate response.

The spread of plastics into the natural world is terrible - humanity polluting literally every corner of the planet. Reducing microplastic airborne particles coming from the degradation of plastic waste, bags, bottles, fishing nets – the ‘Blue Planet’ sources - is potentially a near-impossible task. Reducing plastic-like material that is emitted directly however may be a much more tractable problem. Better road surfaces, lower friction tyres or brake systems that capture dust could all be effective. Tackling this source could have a far bigger public health impact. It needs cool and objective research to determine where the biggest policy bang per buck will lie.

We know in public health that emerging problems can get more attention than well-established ones, because of the shiny factor. We also know that context-free statistics are everywhere, particularly at the moment with Covid-19. There are parallels between risk communication on plastics and Covid-19 vaccines. Of course, microplastics are likely to be harmful to health, as are vaccine side effects. But when you look at the risks in totality, the position can look different. In neither case does this means the issues should be ignored, or not researched, or not reported. But without context, decision making for the general public, government etc can be pulled off in the wrong direction.

This paper will present the latest understanding of particle impacts setting the microplastics issue in context, and will draw parallels with recent examples of risk communication associated with COVID-19 and the vaccine response. There is a huge amount known about particle pollution and public health, and much of that knowledge has been around for 40 years. We mustn’t get too distracted by the novel, when there is so much we could do to fix those things we already know to be bad for our health.

The authors are a public health doctor who has been at the forefront of the Covid-19 response in the UK and a leading academic in Atmospheric Science.

Climatology of Lightning Strikes in Germany from 2009 - 2020

Lauren Rootham

Lightning strikes are the main causes of forest fires in Germany. However, to date, no studies have utilised statistical analyses, such as Principle Component Analysis (PCA) and Cluster Analysis (CA), to examine the spatial variability and regionality of lightning strikes within the country. Using Arrival Time Difference Network (ATDnet) lightning data, this study will map lightning variability within Germany using PCA and create a regionalisation of lightning using CA. Stepwise linear regression modelling will also be undertaken. Such study will aim to fill a gap in the knowledge, providing a comprehensive climatology of lightning strikes, which may be beneficial for forest fire mitigation and response planning agencies.


Sensitivity Analysis of Hazard Impact Model Vulnerability Inputs

Dr Faye Wyatt, Senior Weather Impact Scientist, Met Office

The Vehicle Overturning (VOT) Model is a prototype Hazard Impact Model (HIM) designed to forecast the risk of vehicles being overturned due to strong winds. Incidents of this type have the potential to disrupt major roads across Great Britain. The probabilistic version of the model has been running continuously since late 2013, with outputs available to operational meteorologists to assist with the issuance of impact-based warnings.

Hazard Impact Models are one of several different methodological options that can be used to support impact-based warnings. To better understand the robustness and appropriateness of the Hazard Impact Modelling approach, a review of 3.5 years of archived VOT model data was undertaken. Initial comparisons with issued National Severe Weather Warning Service (NSWWS) impact-based warnings highlighted the necessity for a thorough review of model input data, and particularly the vulnerability and exposure information. To address this, a sensitivity analysis of the VOT Model has been undertaken.

Utilising the component datasets of the vulnerability index to produce a range of alternative model inputs, this analysis explores the relative contribution of each component of vulnerability to VOT risk. Using archived data, a range of experiments have been run to generate new risk outputs for over three hundred model runs. These experimental model outputs were subsequently used to undertake both a local One-At-a-Time (OAT) sensitivity analysis to determine the influence of individual components of vulnerability on VOT risk, and a Global sensitivity analysis to investigate the relative importance of hazard, vulnerability, and exposure on risk scores.

This presentation will describe current progress, highlighting methods and tools used, challenges encountered and preliminary results.