AMMA Further Analysis: Convective life-cycles over African continental surfaces
Lead Research Organisation:
University of Leeds
Department Name: School of Earth and Environment
Abstract
The population of West Africa rely on rainfall for their survival, since rainfall in most areas is the most important limit on agricultural production. Rainfall is also important in the availability of water for human consumption and for hydroelectric power generation, while the seasonal rainfall influences certain diseases such as malaria. Currently, our ability to predict rainfall in this region is extremely poor. This project aims to improve our understanding of the rain-bringing storms of West Africa, and improve our ability to forecast them. Through a knowledge-exchange programme with weather forecasters from the UK and West Africa, we will feed the new scientific understanding into daily and longer-term predictions. In the Sahel region during the monsoon season, most of the rain is delivered by large thunderstorm clouds, known as cumulonimbus, which can extend 20 kilometres upwards into the atmosphere. These cumulonimbus clouds band together into large, organised storms, several hundred km in extent, that produce intense rain, leading to patches of very wet soil. Often, after a storm, patches of wet soil lie adjacent to soil which remains extremely dry. In turn, the soil moisture patterns lie on top of a mixed distribution of vegetation, from forest to agriculture, savanna and desert. We know that such patterns in the land surface can interact with storms on the following days, and it is important to understand these processes for accurate weather forecasting. In the past, a major problem in quantifying this interaction between the land surface and cloud has been a lack of useful measurements from this remote region. Following the successful NERC-funded AMMA (African Monsoon Multidisciplinary Analysis) study, we now have unprecedented observational data for this region of the continental tropics. Using this dataset, we will analyse cases in which storms interact with the land surface, and therefore improve weather prediction models. The West African Monsoon is an airflow which brings humid air from the Atlantic Ocean into the continent: this humidity feeds the rain-bringing storms. However, moisture is also transported out of the low level, humid monsoon layer by smaller clouds, known as cumulus congestus. The rate at which moisture is mixed upwards by congestus clouds influences the water budget of the entire West African region, so we need to assess their effects if we are to get the forecast right. We will make use of chemical tracers measured during AMMA, to understand and evaluate the rates of congestus mixing, in reality and in models. We will use the UK Met Office weather and climate prediction model - the 'Unified Model' (UM). The UM is excellent for this kind of study because it can be used to describe a wide range of phenomena in the atmosphere, from small clouds a kilometre or so across, or the whole global atmosphere. Advances made in a sister project (Cascade) mean that now we have a version of the UM which can resolve clouds right across the continent, and assess the interactions between these clouds. Such interactions are just as important as the land surface state in setting off new storms -a big thunderstorm sets of patterns of waves in the atmosphere which move thousands of km across the continent and may commonly set off a new storm at a remote location. By resolving these processes in the Cascade version of the UM, we aim to understand what is needed to get them right in a weather prediction version of the UM. The UM is also used as a climate prediction model: currently, climate predictions for West Africa disagree on projections of future rainfall, which hinders effective mitigation strategies that could help in planning for local and international governments. The knowledge gained from this project will help not only in the day-to-day prediction of storm events but also in prediction of future rainfall trends.
Publications
Provod M
(2016)
A Characterization of Cold Pools in the West African Sahel
in Monthly Weather Review
Birch C
(2014)
A seamless assessment of the role of convection in the water cycle of the West African Monsoon WEST AFRICAN WATER CYCLE
in Journal of Geophysical Research: Atmospheres
Taylor C
(2012)
Afternoon rain more likely over drier soils
in Nature
Polcher J
(2011)
AMMA's contribution to the evolution of prediction and decision-making systems for West Africa
in Atmospheric Science Letters
Bhowmick M
(2018)
Analytical solution to a thermodynamic model for the sensitivity of afternoon deep convective initiation to the surface Bowen ratio
in Quarterly Journal of the Royal Meteorological Society
Bain C
(2011)
Anatomy of an observed African easterly wave in July 2006
in Quarterly Journal of the Royal Meteorological Society
Mari C
(2011)
Atmospheric composition of West Africa: highlights from the AMMA international program
in Atmospheric Science Letters
Bourgeois E
(2018)
Characteristics of mid-level clouds over West Africa
in Quarterly Journal of the Royal Meteorological Society
Berkes F
(2012)
Convective Squalls over the Eastern Equatorial Atlantic
in Weather and Forecasting
Klüpfel V
(2011)
Convergence zones and their impact on the initiation of a mesoscale convective system in West Africa
in Quarterly Journal of the Royal Meteorological Society
Lavender S
(2010)
Coupled Land-Atmosphere Intraseasonal Variability of the West African Monsoon in a GCM
in Journal of Climate
Marsham J
(2015)
Disagreements in Low-Level Moisture between (Re)Analyses over Summertime West Africa
in Monthly Weather Review
Danuor S
(2011)
Education in meteorology and climate sciences in West Africa
in Atmospheric Science Letters
Spracklen D
(2013)
Erratum: Corrigendum: Observations of increased tropical rainfall preceded by air passage over forests
in Nature
Taylor CM
(2017)
Frequency of extreme Sahelian storms tripled since 1982 in satellite observations.
in Nature
Taylor C
(2011)
Frequency of Sahelian storm initiation enhanced over mesoscale soil-moisture patterns
in Nature Geoscience
Garcia-Carreras L
(2011)
How does local tropical deforestation affect rainfall? DEFORESTATION AND RAINFALL
in Geophysical Research Letters
Garcia-Carreras L
(2010)
Impact of mesoscale vegetation heterogeneities on the dynamical and thermodynamic properties of the planetary boundary layer
in Journal of Geophysical Research
Birch C
(2012)
Impact of soil moisture and convectively generated waves on the initiation of a West African mesoscale convective system
in Quarterly Journal of the Royal Meteorological Society
Taylor C
(2010)
Impact of soil moisture on the development of a Sahelian mesoscale convective system: a case-study from the AMMA Special Observing Period
in Quarterly Journal of the Royal Meteorological Society
Janicot S
(2011)
Intraseasonal variability of the West African monsoon
in Atmospheric Science Letters
Lafore J
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Cornforth R
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Lafore J
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Parker D
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Taylor C
(2013)
Modeling soil moisture-precipitation feedback in the Sahel: Importance of spatial scale versus convective parameterization
in Geophysical Research Letters
Pearson K
(2013)
Modelling the diurnal cycle of tropical convection across the 'grey zone'
in Quarterly Journal of the Royal Meteorological Society
Taylor C
(2011)
New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis
in Atmospheric Science Letters
Spracklen DV
(2012)
Observations of increased tropical rainfall preceded by air passage over forests.
in Nature
Bain C
(2010)
Observations of the Nocturnal Boundary Layer Associated with the West African Monsoon
in Monthly Weather Review
Fitzpatrick R
(2016)
On What Scale Can We Predict the Agronomic Onset of the West African Monsoon?
in Monthly Weather Review
Fink A
(2011)
Operational meteorology in West Africa: observational networks, weather analysis and forecasting
in Atmospheric Science Letters
Lafore J
(2011)
Progress in understanding of weather systems in West Africa
in Atmospheric Science Letters
Wang C
(2011)
Properties of a simulated convective boundary layer over inhomogeneous vegetation
in Quarterly Journal of the Royal Meteorological Society
Kergoat L
(2011)
Remote sensing of the land surface during the African Monsoon Multidisciplinary Analysis (AMMA)
in Atmospheric Science Letters
Hartley A
(2016)
Simulation of vegetation feedbacks on local and regional scale precipitation in West Africa
in Agricultural and Forest Meteorology
Messager C
(2010)
Structure and dynamics of the Saharan atmospheric boundary layer during the West African monsoon onset: observations and analyses from the research flights of 14 and 17 July 2006 SAHARAN ATMOSPHERIC BOUNDARY LAYER AT MONSOON ONSET
in Quarterly Journal of the Royal Meteorological Society
Lohou F
(2014)
Surface response to rain events throughout the West African monsoon
in Atmospheric Chemistry and Physics
Lebel T
(2011)
The AMMA field campaigns: accomplishments and lessons learned
in Atmospheric Science Letters
Grams C
(2010)
The Atlantic inflow to the Saharan heat low: observations and modelling
in Quarterly Journal of the Royal Meteorological Society
Abdou K
(2010)
The diurnal cycle of lower boundary-layer wind in the West African monsoon LOWER BOUNDARY-LAYER WIND IN THE WEST AFRICAN MONSOON
in Quarterly Journal of the Royal Meteorological Society
Dixon N
(2013)
The effect of background wind on mesoscale circulations above variable soil moisture in the Sahel Effect of Background Wind on Mesoscale Circulations
in Quarterly Journal of the Royal Meteorological Society
Birch C
(2012)
The effect of orography and surface albedo on stratification in the summertime Saharan boundary layer: Dynamics and implications for dust transport
in Journal of Geophysical Research: Atmospheres
Tompkins A
(2012)
The Ewiem Nimdie Summer School Series in Ghana: Capacity Building in Meteorological Education and Research-Lessons Learned and Future Prospects
in Bulletin of the American Meteorological Society
Cornforth R
(2019)
The First Forecasters' Handbook for West Africa
in Bulletin of the American Meteorological Society
Burton R
(2012)
The Harmattan over West Africa: nocturnal structure and frontogenesis
in Quarterly Journal of the Royal Meteorological Society
Garcia-Carreras L
(2013)
The impact of convective cold pool outflows on model biases in the Sahara IMPACT OF COLD POOLS ON MODEL BIASES
in Geophysical Research Letters
Garcia-Carreras L
(2015)
The Impact of Parameterized Convection on the Simulation of Crop Processes
in Journal of Applied Meteorology and Climatology
| Description | The project has used field measurements to test weather and climate forecast models over West Africa. We have made some important steps in understanding the links between land surface state and rainfall, in West Africa. These are results which appear to hold in all the tropical continental regions. We find that afternoon rain is favoured over dry surfaces, and suppressed over cooler, moist surfaces. This means that after rainfall, rain on the subsequent days is more likely to be initiated over areas which remained dry. The results also apply to the control of rainfall by vegetation: when forest is cleared for farming, rainfall is increased over the cleared areas, but decreases over the remaining forests. We speculate that this effect may put stress on the survival of the remaining forest. We have developed case studies of the atmospheric response to surface patterns of vegetation and soil moisture, and the ways in which this response conditions the rainfall on the next day. We have also made statistical analysis of satellite observations and high-resolution models, to show that the land-atmosphere coupling is robust over many rainfall events. We have shown that current climate models have the wrong sign of response of the rainfall to surface wetness: this is a major concern in the interpretation of model projections of the water cycle over the tropical continents in a future climate. We have also shown that high-resolution models capture the feedbacks faithfully, and we have quantified the implications of the errors for the prediction of future drought periods in Africa. We have used the latest generation of high-resolution models to explain how climate models handle the water cycle of the region, including the feedbacks between rain-bringing storms and the surface state. |
| Exploitation Route | Our results offer methodologies for the planning of future land use in the tropics, in relation to its influence on rainfall. Our results are directly relevant to the improvement of global weather and climate models, and are being used to develop these models through our partnership with the Met Office. The methodologies developed in this project are also being used in a number of spin-off research activities, such as a project with the Met Office, analysing the changes in rainfall which result from changing land-cover in Africa. We are developing the material into guidance for weather forecasters as part of our Impact Plan. This includes leading a new textbook on weather forecasting in West Africa. |
| Sectors | Environment |
| Description | The findings of this project have been used in the weather and climate prediction services, in the UK, Europe and within Africa. Our results have also pointed out fundamental physical processes which need to be represented in models of the climate system, in order to correctly link the land surface, rainfall, and large-scale circulations. These results are influencing the development of the next generation of models for the Met Office. As part of the Impact Plan for this project, we have led the preparation of a "Forecasters' Handbook for West Africa";. This project is a major knowledge exchange between researchers and forecasters, in Africa and around the world, and will be used to train the next generation of weather forecasters in Africa. This is a unique resource for weather forecasting, globally. The book was published in April 2017. https://www.wiley.com/en-gb/Meteorology+of+Tropical+West+Africa%3A+The+Forecasters%27+Handbook-p-9781118391303 The book was translated into French and published in 2018: https://laboutique.edpsciences.fr/produit/1038/9782759821808/Meteorologie%20de%20lAfrique%20de%20lOuest%20tropicale More than 300 copies have been supplied to the African weather services and training centres, funded by the Met Office and Meteo-France. The book and its methods are now being used in the Regional Training School at Oshodi, Lagos. |
| First Year Of Impact | 2014 |
| Sector | Aerospace, Defence and Marine,Environment,Transport |
| Impact Types | Societal,Economic |
| Description | Forecasters' Handbook for West Africa |
| Geographic Reach | Africa |
| Policy Influence Type | Influenced training of practitioners or researchers |
| Impact | We have published a textbook for the training of forecasters in the field of African meteorology. This is the first such book of its kind anywhere in the world, and targets one of the most environmentally vulnerable regions. The book was generated as a Knowledge Exchange activity associated with the AMMA project (several NERC and other funded projects), bringing together forecasters and researchers from Africa, the EU and USA. It has been supplied to weather services and training centres in Africa and we are working to embed the material into the syllabus of training programmes in the weather services and universities in Africa. The outcomes of this are intended to be improved skills of weather forecasters, and improved predictions, benefitting vulnerable people in Africa, as well as some major economic sectors in the region, including power generation, agriculture, fisheries and transport. |
| Description | Forecasting methods described in the Forecasters' Handbook are being used for training of forecasters in Africa, and in other tropical locations. |
| Geographic Reach | Multiple continents/international |
| Policy Influence Type | Influenced training of practitioners or researchers |
| Impact | In the Forecasters' Handbook, we formalised methods for plotting of weather charts for West Africa. The methods have been subsequently (in the GCRF African SWIFT project) been used to develop training materials for forecasters: these materials have been used in training events, and are now used in the forecaster Regional Training Centre at Oshodi, Lagos. We have adapted the methods and used them for forecaster training in SE Asia (FORTIS project) and the Caribbean (EUREC4A project). |
| Description | International funding for Forecasting Workshop in West Africa |
| Amount | £54,460 (GBP) |
| Organisation | Meteorological Office UK |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | 03/2013 |
| End | 03/2013 |
| Description | International funding for Forecasting Workshop in West Africa |
| Amount | £54,460 (GBP) |
| Organisation | Meteorological Office UK |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | 03/2013 |
| End | 03/2013 |
| Description | CEH-Leeds |
| Organisation | UK Centre for Ecology & Hydrology |
| Country | United Kingdom |
| Sector | Public |
| PI Contribution | My team in Leeds conduct atmospheric studies using observations, models and theoretical ideas. I have also led a number of projects and field experiements in which we have collaborated with CEH. |
| Collaborator Contribution | Expertise in land-surface processes. Expertise in land-atmosphere interactions. Expertise in land-atmosphere climate dynamics. Data analysis, especially remote sensing of rainfall and land surface state. Leadership of projects. Co-supervision of PhD students. |
| Impact | This is a multidisciplinary partnership in the area of land-atmosphere interaction. It has resulted in a large number of high-impact papers, successful jointly-supervised PhD studentships, and successful impacts, especially in Africa. |
| Description | Met Office |
| Organisation | Meteorological Office UK |
| Country | United Kingdom |
| Sector | Academic/University |
| 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. |