Saharan - West African Monsoon Multi-scale Analysis (SWAMMA)

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

The West African Monsoon is critical to the livelihoods of millions, but remains a major challenge for weather and climate prediction. The monsoon provides moisture for large systems of thunderstorms that provide the annual rainfall in the Sahel. The monsoon is driven by the summertime heating over the continent. The Sahara exhibits the highest summertime temperatures and it is known that the monsoon is sensitive to the heating in the Sahara and the Sahel. The heating in the Sahara is controlled by dust, cloud and ventilation by colder air from the Sahara's margins. It is known that models exhibit major differences in this region, which is for example important for monsoon onset, but historically there has been an absence of data with which to evaluate models.

Recent research has shown that the monsoon, dust and the storm-systems form a fully coupled system and that global models exhibit major biases in the couplings within this system. Operational models fail to capture the organisation, location and timing of the monsoon rains and this leads to incorrect coupling between the storm systems and the monsoon. Operational models also fail to represent the haboob dust storms generated by the storm systems, which are likely the main driver of dust emission in the summer. This means that even operational models which include dust fail to accurately capture the impacts of the dust on the meteorology, since a major dust emission mechanism is missing in the models. Recent research has also shown the existence of larger dust particles over the Sahara than previously observed, which will affect heating rates, feeding back on to the meteorology.

SWAMMA will bring together a recently-developed model that can for the first time capture these couplings with recently-acquired data from this highly data-sparse region (collected during the NERC-funded AMMA and Fennec projects). SWAMMA will therefore combine for the first time a model that should be able to represent the key features of the summertime energy budget of the monsoon system with the first data sufficient to evaluate such a model.

SWAMMA will evaluate the new model, quantifying the winds that generate dust uplift in the Sahara and Sahel. It will use the new data to analyse the impacts of variations in the sizes of dust particles. SWAMMA will evaluate the energy budgets of the monsoon system using both models and observations from AMMA and Fennec. SWAMMA will quantify how the coupled processes of the monsoon system respond to the seasonal evolution of the monsoon's boundary conditions to control the seasonal stability of the monsoon rainfall and its variability. By bringing together the recently-acquired data and the new model with existing weather and climate models the project will evaluate how process errors in operational models lead to systematic errors in predictions, both over West Africa and globally. The project will provide metrics for the processes that must be captured by operational models for them to capture the key processes and couplings in the West African monsoon system.

Planned Impact

SWAMMA research will benefit operational weather and climate prediction centres worldwide, indirectly benefiting all users of their predictions, most obviously in the West African Monsoon (WAM) region, but also globally. Errors in tropical convection are known to be a major source of error in all global models, particularly in monsoon regions. Dust is a significant source of error in weather prediction and an important Earth-system component. Dust is increasingly being included in operational weather and climate models. SWAMMA will therefore benefit Earth-system science, as well as weather and climate.

Forecasting the annual monsoon rains, and particularly their onset or breaks during the season, is the most urgent requirement of weather prediction systems for the region. SWAMMA will quantify the balance of processes that determine the WAM state as it evolves through the seasonal cycle. Studying the three years with sufficient data will allow an assessment of inter-annual variability. SWAMMA will generate metrics for the processes that global models must represent to capture the evolution of the monsoon. SWAMMA will use the Met Office Unified Model (UM), but the process coupling errors identified in the UM are common across global models so the lessons learnt will be applicable to all models.

A strength of SWAMMA is its seamless modelling framework. The UM is both an operational weather and climate model. It is known that errors in low-resolution forecast models correspond closely to errors in climate models, since they are often caused by the same 'fast processes'. SWAMMA will confront new model runs, with a range of resolutions and complexities, with unique field-campaign data, which will for the first time allow detailed model evaluation in the Sahel and Sahara. We will use the process errors diagnosed in the new UM simulations run within SWAMMA to diagnose the sources of error in operational UM weather and climate simulations and determine the global impact of errors in the WAM system. This will provide a robust chain of assessment from observations, through process models to weather and climate predictions. This will inform priorities for operational model development and interpretation of model predictions.

SWAMMA complements the Met Office strategy for developing its convection and dust schemes. Communication with the Met Office will be facilitated by the formal partnerships that exist between the Met Office, Leeds and Reading (with Met Office staff based at both Leeds and Reading) and annual visits of SWAMMA staff to the Met Office. This will allow exchange with scientists working on model development (convection, dynamics and dust) and weather, seasonal, climate and Earth-system predictions.

The main funded phase of AMMA has finished, but AMMA continues to provide international coordination of WAM science. Prof Doug Parker was PI of UK AMMA and SWAMMA will make full use of AMMA to maximise its impact (e.g. attending the AMMA conference). Prof Doug Parker is leading the production of the first WAM forecasters handbook, which will further facilitate exchanges with forecasters and scientists based in West Africa.

Communication with other operational centres will take place through journal papers, conferences and direct communication. John Marsham and Cathryn Birch (a Met Office employee at Leeds) regularly attend (and have given recently plenary talks at, or convened) GASS (Global Atmospheric System Studies), WGNE (Working Group on Numerical Experimentation) and JWCRP (Joint Weather and Climate Research Programme) meetings, which are well attended by scientists in the operational communities. Their ongoing involvement in these fora will facilitate communication with prediction centres worldwide.

Publications

10 25 50
 
Description Paper published showing how (1) meteorological analyses fail to capture the summertime maximum in dust generating winds in the central Sahara, perhaps explaining why global models fail to capture this climatologically significant feature (2) Analysis skill for dust-generating winds is low, especially close to the monsoon front. Skill is reduced in the monsoon season, even for areas not directly influenced by the monsoon. Paper submitted showing when a model is run at high resolution to explicitly capture the haboobs that cause much dust uplift but are not captured in low resolution models, the dust distribution hardly chnages. This occurs because, firstly, the increased windiness in the evening from haboobs is approximately balanced by a reduction in morning winds associated with the breakdown of the nocturnal low-level jet. Secondly, although the haboobs increase the frequency of the strongest winds, these are still weaker than observed, especially close to the observed summertime Saharan dust maximum: this results from the fact that although large convective systems are generated, they have a lower frequency than observed and haboob winds are too weak. Finally, major impacts of the haboobs on winds occur over the Sahel, where, although dust uplift is known to occur in reality, uplift in the simulations is limited by a seasonally constant bare soil fraction in the model, together with soil moisture and clay fractions which are too restrictive of dust emission in seasonally-varying vegetated regions. For future studies, the results demonstrate 1) the improvements in behaviour produced by the explicit representation of convection, 2) the value of simultaneously evaluating both dust and winds and 3) the need to develop parameterisations of the land surface alongside those of dust-generating winds. Paper publsihed showing day-to-day variability in net heating over Sahara is dominaed by water, not dust, showing importance of modelling convection and water vapour transport to modelling the Sahara and the West African monsoon.
Exploitation Route Key finding for other researchers, modellers, operational weather and climate scientists, and those in the solar energy sector, demonstrating the need for improved modelling of haboobs (eg haboob parametrsiation developed in ERC Desert Storms, where SWAMMA has contributed PI time to paper writing, and now being addded to Met Office model in IMPALA) and aspects of land-surface modelling that must be improved for better dust predictions.
Sectors Aerospace, Defence and Marine,Energy,Environment

 
Description SWAMMA identified model vegetation fraction as a possible key source of error for Unified Model dust predictions This led to the Future Climate for Africa Gap-filling project "Veg Flux" , which has used SWAMMA runs as a basis for their runs toinvestigate this question. This should lead to priorisation (or not) of addressing this model error in Met Office Unified Model development (and other weather & climate models)
First Year Of Impact 2018
Sector Environment
 
Description Met Office 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Public 
PI Contribution Our research group analyses atmospheric processes in order to better represent them in the Met Office's forecast models. We also use those forecast models in our research, and evaluate their performance in order to identify the best strategies to improve the models.
Collaborator Contribution The Met Office brings its models and its datasets to the partnership, in addition to the considerable expertise of its staff. The Met Office also represent a conduit to the impact of our research for society, through its provision of operational weather and climate forecasts.
Impact Our research has influenced the Met Office strategy for model development, especially in regard to high-resolution models, and the convective parametrisation scheme. We have jointly influenced international strategy for atmospheric research and measurements.
 
Description NERC fellowship: The role of coarse mineral dust particles in the climate system (NE/M018288/1) 
Organisation University of Reading
Department Department of Archaeology
Country United Kingdom 
Sector Academic/University 
PI Contribution Invited fellow is into all SWAMMA telecons and to co-supervise of Reading SWAMMA PDRA
Collaborator Contribution Fellow is involved in all SWAMMA telecons and co-supervsion of Reading SWAMMA PDRA
Impact None yet. Not multi-disciplinary
Start Year 2016
 
Description AGU - Dec 2017 Can explicit convection improve modelled dust in summertime West Africa? (By Alex Roberts et al) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2017
 
Description American Met. Soc. Annual meeting: The Challenge of Modeling the Meteorology of Dust Emission: Lessons Learned from the Desert Storms Project 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conference presentation
Year(s) Of Engagement Activity 2016
 
Description Article written by Alex Roberts in Conversation about ex Ophelia and the orange sky 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Alex Roberts wrote an article in Conversation about ex Ophelia and the orange sky. Why (ex)Hurricane Ophelia took a wrong turn towards Ireland and Britain - and carried all that dust (published 17.10.17).
Year(s) Of Engagement Activity 2017
URL http://theconversation.com/why-ex-hurricane-ophelia-took-a-wrong-turn-towards-ireland-and-britain-an...
 
Description Conference Poster- The role of moist convection in the West African monsoon system. HDCP, 15-19 February 2016, Berlin, Germany. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The conference poster sparked discussion.
Year(s) Of Engagement Activity 2016
 
Description Conference presentation - Modelling convective dust storms in large-scale weather and climate Models. AGU Fall Meeting, 14-18 December 2015, San Francisco, USA. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Sparked discussion
Year(s) Of Engagement Activity 2015
 
Description Conference presentation - The Role of moist convection in the West African Monsoon. World Weather Open Science Conference, 16-21 August 2014, MontrĂ©al, Canada, SCI-PS211.04. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Sparked debate
Year(s) Of Engagement Activity 2014
 
Description Conference presentation - The challenge of modelling the meteorology of dust emission: Lessons learned from the Desert Storms project. Desert Storms - lessons learned. AGU Fall Meeting, 14-18 December 2015, San Francisco, USA. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Sparked debate.
Year(s) Of Engagement Activity 2015
 
Description EGU2016: Disagreements in low-level moisture between (re)analyses over summertime West Africa 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2016
 
Description EGU2016: Identifying Errors in Dust Models from Data Assimilation over Northern Africa 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2016
 
Description EGU2016: The Challenge of Modelling the Meteorology of Dust Emission: Lessons Learned from the Desert Storms Project 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2016
 
Description EGU2017 - Characteristics of mid-level clouds over West Africa (Elsa Bourgeois et al.) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2017
 
Description EGU2017 - Observations of cross-Saharan transport of water vapour via cycle of cold pools and moist convection (Tomasz Trzeciak et al.) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2017
 
Description EGU2017 - The nocturnal low-level jet in the West African Sahel from observations, analyses, and conceptual models (by Geoffrey Bessardon et al.) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2017
 
Description EGU2017 - The relative importance of water vapour and dust in controlling the variability in radiative heating of the summertime Saharan heat low (by John H. Marsham et al.) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conf presentation
Year(s) Of Engagement Activity 2017
 
Description European Geophys. Union Conf 2016: How well do analyses capture dust-generating winds in the Sahara and Sahel? 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Academic conference presentation
Year(s) Of Engagement Activity 2016
 
Description ICCP2016: Diurnal cycle of moist convection in the West African Monsoon 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Adademic conf presentation
Year(s) Of Engagement Activity 2016
 
Description Meteosat Second Generation conference 2017: Talk, Meteosat Second Generation cloud retrievals evaluated with airborne measurements during Fennec 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Aacdemic talk
Year(s) Of Engagement Activity 2017
 
Description Radio interview on BBC Radio Leeds 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The interview was about the 1987 Great Storm and exOphelia which was being discussed in the news, and included a wider discussion on the orange sky from dust. The total weekly audience figures for Radio Leeds for September (latest figures) was 180,000 listeners (https://media.info/radio/stations/bbc-radio-leeds/listening-figures)
Year(s) Of Engagement Activity 2017
 
Description Windy Day Conference - The Challenge to Model the Meteorology of Dust Emission: Lessons Learnt from the Desert Storms Project 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The Challenge to Model the Meteorology of Dust Emission: Lessons Learnt from the Desert Storms Project
by Alexander Roberts, P. Knippertz, J. Marsham, B. Heinold, K. Schepanski, B. Jemmett-Smith, C. Gilkeson, F. Pantillon, R. Pope, S. Fiedler, S. Cowie
Windy Day 2015
Year(s) Of Engagement Activity 2015