SWAAMI (South West Asian Aerosol Monsoon Interactions)

Lead Research Organisation: University of Reading
Department Name: Meteorology


Aerosol particles from pollution sources across the Indian subcontinent form a dense and extensive haze across India and the Bay of Bengal that increases in extent and magnitude in advance of the monsoon. As the aerosols, a large fraction of which arises from wood and charcoal fired cookstoves, absorb solar radiation as well as scatter it they can affect the heat balance of the lower atmosphere. It has been hypothesised that this aerosol can influence the monsoon through its role in redistribution of heat across the region in the pre-monsoon, and model studies have demonstrated that such effects can be important. However, current comparisons show model to model variability and under-prediction compared to observations, a strong indication that detailed aerosol properties are poorly represented in current models. The lack of accurate representation of aerosol in these models is compounded by a lack of measurements of sufficient accuracy and sensitivity to elucidate fundamental properties such as component mass, mixing state and optical properties, which need to be well characterised to improve model performance. This is limiting predictive capability at the present time and hence preventing the influence of aerosol in the Indian monsoon to be quantified. In addition to reproducing detailed properties of aerosol, models need to be able to accurately represent the horizontal and vertical distribution of different aerosols to predict their effects. As the monsoon progresses, pollution aerosol are removed by precipitation, but also lofted by convection. Dust advected from deserts to the west above the moist monsoonal flow become significant through the season. It is important that these aerosol layers are accurately represented in models and that robust measurements are available to rigorously challenge model predictions.

SWAAMI will contribute to the joint NERC-MoES programme "Drivers of Variability in the Asian Monsoon" through a detailed determination of aerosol physical and chemical properties across India in the advance of, and during, the Indian monsoon using UK and Indian research aircraft. The measurements will deliver a chemical and physical characterisation of the aerosol that is considerably more detailed than any previous and will enable assessment of aerosol composition and mixing state, provide source characterisation and deliver quantification of aerosol optical properties such as extinction, absorption and single scattering albedo. Such detailed characterisation will allow us to test representations of aerosol properties in regional and global climate models. Our planned aircraft measurements will be combined with syntheses of long term data from across the continent and previous field studies to provide a data set that can challenge how well models represent aerosol across the region. Improving model representations of aerosol properties and testing the extent to which this improves model performance against data will provide a framework for ensuring model aerosol schemes improve and in doing so will allow us to make more reliable predictions of aerosols effects on the heat budget of the region and hence improve our knowledge of how aerosols may influence the Indian monsoon.

Planned Impact

Regional climate variability and modification of regional weather, including precipitation, over a region as important as India is a highly significant social, political and scientific issue. The SWAAMI project will therefore have significant impact across a wide spectrum of stakeholders.

Who will benefit from this research?

Scientific community. This work will be of significant scientific interest nationally and internationally, in particular this work will benefit Indian and UK science and mutual benefit will be derived between SWAAMI and the wider MoES and NERC communities not just across the "Drivers of Variability in the Indian Monsoon" programme.

Operational Weather Forecasting Centres: SWAAMI is a direct collaboration with several research groups in the Met Office and will have a direct feed through to future improvements in Numerical Weather Prediction and Climate modelling.

General public/media. There has been significant publicity in recent years on aerosols, clouds and climate and also on India, pollution from cookstoves and the Indian monsoon and lastly on whether reducing black carbon emissions has the dual benefit of improving air quality and reducing regional and global warming. However, there remains significant lack of knowledge surrounding these issues and clear information needs to be conveyed to the public.

Policymakers: There is considerable interest from policy-makers on the impacts of absorbing aerosol on the radiative forcing of climate with suggestions for black carbon emission reduction as a mitigation strategy to counter global warming.

How will they benefit?

Scientific community. New ground based and airborne measurements over India will be important for the scientific community. Aerosol processes in models will be tested in an extremely important environment - the Indian subcontinent. Project results will be widely reported in publications, international conferences etc. Project results will feed into future IPCC assessments through modelling studies such as future equivalents of CMIP5 and AEROCOM.

Operational Weather Forecasting Centres: The UK Met Office is a key partner and beneficiary of SWAAMI science. The Met Office Observational Based Research Group will participate in the NERC-MoES experiment and has dedicated substantial flying hours to the project. The outcomes of the project will directly feed Met Office activities in the areas of Global Model Evaluation and Development, where SWAAMI will provide data to support the inclusion and testing of absorbing aerosols in operational Numerical Weather Prediction models. The Earth System and Mitigation Science Group will make use of SWAAMI outcomes to test its new aerosol scheme being developed within the Hadley Centre.

General public/media. Raising awareness of the role of absorbing aerosols and black carbon on regional climate and as a rapid solution for mitigating climate warming, in addition to improving air quality, will be performed by media interviews and press releases during the project. Articles for popular science magazines will also be produced. We will use podcasts and other web technologies to reach a wide audience. Local events such as national science week and presentations to local schools enhance the outreach from this project. We would hope to increase these opportunities to offer similar communication to people in India.

Policymakers: Project PIs have provided advice to the UK government, contributed to EU policy committees, as well as to IPCC and WMO panels and assessments. Many opportunities exist for SWAAMI scientists to raise awareness of the role of absorbing aerosols over India. In addition, project PDRAs will be encouraged to participate in the various 'science into policy' schemes that exist with the Royal Society and NERC. The measurement and modelling integration will provide policy makers with evidence for potential effectiveness of mitigation strategies.


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Description We have discovered that the research version of the Met Office Numerical Weather Prediction Model produced for SWAAMI project performed reasonably well compared to satellite observations in terms of aerosol optical depth and very well in terms of a measure of the size of the aerosol when compared to ground based measurements. However, there was a tendency for a difference in aerosol optical depth to occur when the winds in the model were too westerly which brought a lot of dust into the region from the west. The model winds tend to be too west to east, not sending aerosol towards Southern India. The position of Bay of Bengal cyclones in the model was crucial for easterly wind component which was also linked to biases in aerosol optical depth in northern India.

We have performed a number of experiments with an intermediate-complexity climate model to investigate the influence of different aerosol species, and different aerosol locations, on the Indian summer pre-monsoon period. We find that increasing aerosol optical depth over India causes precipiation to decrease and temperature to increase across India. However, when absorbing aerosol is increased over both India and China competing circulation changes act to suppress the precipitation response. Indian precipitation was found to be relatively more sensitive to changes in absorbing aerosol compared to scattering aerosol.
Exploitation Route Use for developing models.
Further uptake of the intermediate-complexity approach for understanding the atmospheric circulation response to aerosol changes.
Sectors Environment,Healthcare

Title IGCM simulations 
Description Simulations using the Reading Intermediate GEneral Circulation Model with idealised aerosol distribution over India and mixed layer ocean. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? No  
Impact This will form the basis of a publication under preparation in 2019. 
Description Indian Institute of Science 
Organisation Indian Institute of Science Bangalore
Department Centre for Atmospheric and Oceanic Sciences
Country India 
Sector Academic/University 
PI Contribution Exchange of information and analysis suggestions
Collaborator Contribution Data from Indian aircraft and exchange of information and analysis suggestions.
Impact none yet - in development.
Start Year 2015
Description SWAAMI met office 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Academic/University 
PI Contribution We are evaluating a forecast model's performance in predicting Aerosol optical depth,
Collaborator Contribution Running the forecast model and providing the output data
Impact None yet
Start Year 2016
Description Contributed slides to Hugh Coe's talk at the Royal Meteorological Society National Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact Contributed slides to Royal Meteorological Society National Meeting presented by Hugh Coe, University of Manchester.
Year(s) Of Engagement Activity 2018