Fennec - The Saharan Climate System
Lead Research Organisation:
University of Leeds
Department Name: School of Earth and Environment
Abstract
The central Sahara has one of the most extreme climates on Earth. During the northern summer months, a large low pressure system caused by intense sunshine develops over a huge, largely uninhabited expanse of northern Mali, southern Algeria and eastern Mauritania. Temperatures in the high 40s are normal and uplift of dry air through more than 6000m of the atmosphere is routine in what is thought to be the deepest such layer on the planet. This large zone is also where the thickest layer of dust anywhere in the Earth's atmosphere is to be found. Although the central Sahara is extremely remote, it turns out to be vitally important to the world's weather and climate. The large low pressure system drives the West African Monsoon and the dry, dusty air layers are closely related to the tropical cyclones which form over the Atlantic Ocean. Likewise, the dusty air has a strong influence on the way the atmosphere is heated, a process which is poorly understood. It is not surprising that the models we use to predict weather and climate and which are a crucial tool for understanding how the atmosphere works, all have problems in dealing with the central Sahara. Insights into how the climate system works, improving the models and therefore the predictions have all been held back in the case of the Sahara by a lack of measurements of the atmosphere and the processes that make dust and extreme weather. This will always be the case until a team goes to the central Sahara and makes these measurements. A key part of this proposal aims to do just that. We want to set up an array of special instruments, at the surface in two carefully chosen places in the central Sahara, which will monitor the winds, temperatures, dust and so on for an entire year. We will add to this collection for a shorter period of even more intense measurements during the core summer month of June. We plan also to fly a instruments attached to an aeroplane overhead the surface array and across the desert so that we can get an idea of the structure of the atmosphere and how it changes through the day. To find out how dust storms work, we will leave 10 weather stations at places where we think dust storms happen frequently. Satellites play an essential role in measuring weather and climate and are especially useful in remote places. The best available information from satellites will help to quantify how weather and climate works in the Sahara. We also expect to improve the way the satellites are able to make their measurements too. Because models are so important to understanding and predicting weather, we will make heavy use of them in this work. We want to know how well the models work over the Sahara and what can be done to improve them. We are especially interested in seeing whether the models work better if we allow them to deal with small parts of the climate system or whether we can still represent extreme places in the Sahara by ignoring these details in the models.
Publications
Allen C
(2013)
Dust emission and transport mechanisms in the central Sahara: Fennec ground-based observations from Bordj Badji Mokhtar, June 2011
in Journal of Geophysical Research: Atmospheres
Allen C
(2015)
Dust detection from ground-based observations in the summer global dust maximum: Results from Fennec 2011 and 2012 and implications for modeling and field observations
in Journal of Geophysical Research: Atmospheres
Allen C
(2014)
The low-level jet dust emission mechanism in the central Sahara: Observations from Bordj-Badji Mokhtar during the June 2011 Fennec Intensive Observation Period Central Saharan LLJ dust emission
in Journal of Geophysical Research: Atmospheres
Ashpole I
(2013)
A new high-resolution central and western Saharan summertime dust source map from automated satellite dust plume tracking
in Journal of Geophysical Research: Atmospheres
Ashpole I
(2012)
An automated dust detection using SEVIRI: A multiyear climatology of summertime dustiness in the central and western Sahara
in Journal of Geophysical Research: Atmospheres
Ashpole I
(2013)
Intraseasonal variability and atmospheric controls on daily dust occurrence frequency over the central and western Sahara during the boreal summer
in Journal of Geophysical Research: Atmospheres
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
Blechschmidt A
(2012)
Aircraft-based observations and high-resolution simulations of an Icelandic dust storm
in Atmospheric Chemistry and Physics
Bourgeois E
(2018)
Characteristics of mid-level clouds over West Africa
in Quarterly Journal of the Royal Meteorological Society
Burton R
(2012)
The Harmattan over West Africa: nocturnal structure and frontogenesis
in Quarterly Journal of the Royal Meteorological Society
Caton Harrison T
(2019)
A 14-Year Climatology of Saharan Dust Emission Mechanisms Inferred From Automatically Tracked Plumes
in Journal of Geophysical Research: Atmospheres
Chédin A
(2020)
Contribution of IASI to the Observation of Dust Aerosol Emissions (Morning and Nighttime) Over the Sahara Desert
in Journal of Geophysical Research: Atmospheres
Cornforth R
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Cornforth R
(2019)
The First Forecasters' Handbook for West Africa
in Bulletin of the American Meteorological Society
Cowie SM
(2013)
Are vegetation-related roughness changes the cause of the recent decrease in dust emission from the Sahel?
in Geophysical research letters
Crumeyrolle S
(2011)
Transport of dust particles from the Bodélé region to the monsoon layer - AMMA case study of the 9-14 June 2006 period
in Atmospheric Chemistry and Physics
Engelstaedter S
(2015)
The Saharan heat low and moisture transport pathways in the central Sahara-Multiaircraft observations and Africa-LAM evaluation
in Journal of Geophysical Research: Atmospheres
Englehardt S
(2013)
Water Surface Topography Retrieved from Color Images*
in Journal of Atmospheric and Oceanic Technology
Garcia-Carreras L
(2013)
The impact of convective cold pool outflows on model biases in the Sahara
in Geophysical Research Letters
Garcia-Carreras L
(2015)
The Turbulent Structure and Diurnal Growth of the Saharan Atmospheric Boundary Layer
in Journal of the Atmospheric Sciences
Gross A
(2015)
Variability in Sources and Concentrations of Saharan Dust Phosphorus over the Atlantic Ocean
in Environmental Science & Technology Letters
Heinold B
(2013)
The role of deep convection and nocturnal low-level jets for dust emission in summertime West Africa: Estimates from convection-permitting simulations.
in Journal of geophysical research. Atmospheres : JGR
Huang Q
(2010)
Simulations of the effects of surface heat flux anomalies on stratification, convective growth, and vertical transport within the Saharan boundary layer
in Journal of Geophysical Research: Atmospheres
Huang Q
(2018)
Large-eddy simulation of dust-uplift by a haboob density current
in Atmospheric Environment
Johnson B
(2012)
In situ observations of volcanic ash clouds from the FAAM aircraft during the eruption of Eyjafjallajökull in 2010
in Journal of Geophysical Research: Atmospheres
Kealy J
(2017)
Clouds over the summertime Sahara: an evaluation of Met Office retrievals from Meteosat Second Generation using airborne remote sensing
in Atmospheric Chemistry and Physics
Lafore J
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Lafore J
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Marsham J
(2016)
The contrasting roles of water and dust in controlling daily variations in radiative heating of the summertime Saharan heat low
in Atmospheric Chemistry and Physics
Marsham J
(2013)
Meteorology and dust in the central Sahara: Observations from Fennec supersite-1 during the June 2011 Intensive Observation Period
in Journal of Geophysical Research: Atmospheres
Marsham J
(2011)
The importance of the representation of deep convection for modeled dust-generating winds over West Africa during summer SUMMERTIME DUST UPLIFT OVER WEST AFRICA
in Geophysical Research Letters
Parker D
(2017)
Meteorology of Tropical West Africa - The Forecasters' Handbook
Redl R
(2016)
Weakening and moistening of the summertime Saharan heat low through convective cold pools from the Atlas Mountains
in Journal of Geophysical Research: Atmospheres
Roberts A
(2017)
New Saharan wind observations reveal substantial biases in analysed dust-generating winds
in Atmospheric Science Letters
Robinson N
(2012)
The lofting of Western Pacific regional aerosol by island thermodynamics as observed around Borneo
in Atmospheric Chemistry and Physics
Rocha-Lima A
(2018)
A detailed characterization of the Saharan dust collected during the Fennec campaign in 2011: in situ ground-based and laboratory measurements
in Atmospheric Chemistry and Physics
Rosenberg P
(2014)
Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements AIRCRAFT MEASUREMENTS OF DUST FLUX
in Journal of Geophysical Research: Atmospheres
Rosenberg P
(2012)
Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign
in Atmospheric Measurement Techniques
Rosenberg P.D.
(2014)
Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements
in Journal of Geophysical Research
Ryder C
(2013)
Optical properties of Saharan dust aerosol and contribution from the coarse mode as measured during the Fennec 2011 aircraft campaign
in Atmospheric Chemistry and Physics
Ryder C
(2013)
Impact of atmospheric transport on the evolution of microphysical and optical properties of Saharan dust
in Geophysical Research Letters
Ryder C
(2015)
Advances in understanding mineral dust and boundary layer processes over the Sahara from Fennec aircraft observations
in Atmospheric Chemistry and Physics
Sodemann H
(2015)
Lagrangian dust model simulations for a case of moist convective dust emission and transport in the western Sahara region during Fennec/LADUNEX
in Journal of Geophysical Research: Atmospheres
Stein T
(2011)
The vertical cloud structure of the West African monsoon: A 4 year climatology using CloudSat and CALIPSO WEST AFRICAN MONSOON CLOUD STRUCTURE
in Journal of Geophysical Research: Atmospheres
Description | The Fennec field campaign has provided the first ever comprehensive dataset of climatic conditions over the Sahara. These data are being used to explain the physics of the climatic system in this region, and to evaluate our models of that system. We have shown that "cold pools" of air moving into the desert at low levels, from thunderstorms on the margins of the desert, have a significant impact on the temperature structure of the region and are not represented in climate models. This helps to explain the biases in those models. These results have influenced the strategy of climate modelling centres, to include cold-pools in their models. We have used observations and models to describe the physics of the Saharan atmospheric boundary layer. We have found that there is a fundamentally different physical evolution over the Sahara, which leads to biases in the weather and climate models. We have also developed new techniques to measure, for the first time from an airborne platform, the emissions of dust from a desert surface. We have used the surface data, along with satellite data, to show that water vapour is the primary control on the energy balance of the Sahara. This is a surprising result, becuase the Sahara is a very dry place. It is very important in the African climate system. Notably, in comparing water vapour and airborne dust, we find that the water vapour has a much larger contribution to variations in the heating of the Saharan atmosphere than the dust, contrary to the expectations of many scientists. |
Exploitation Route | The results are being used by the Met Office and other operational forecasting centres to improve their weather and climate prediction models. |
Sectors | Environment |
Description | Our findings are being used by the UK Met Office to improve their models. This includes a new strategy to include convective "cold pools" in their convection scheme, and a consideration of the need for modified entrainment over the desert. |
First Year Of Impact | 2011 |
Sector | Environment |
Impact Types | Economic |
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 | 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. |