Final Report Summary - DESERTSTORMS (Desert Storms - Towards an Improved <br/>Representation of Meteorological Processes in <br/>Models of Mineral Dust Emission)
Mineral dust particles, lifted from the world’s deserts and sometimes transported over thousands of kilometres around the globe, play an important role in the Earth system and significantly affect weather and climate through their influences on solar and thermal radiation, the formation of droplets and ice particles in clouds, chemical reactions in the atmospheric and the carbon cycle via the fertilization of ecosystems. Recently increasing efforts have been made to include effects of dust into a wide range of modelling tools. Nevertheless, quantitative estimates of dust emission and deposition are highly uncertain. This is largely due to the lack of sufficient observational data and the strongly nonlinear dependence of emissions on peak winds, which are often underestimated in computer models and even analysis data.
The Desert Storms project funded by the European Research Council and led by Peter Knippertz at the Karlsruhe Institute of Technology and by John Marsham at the University of Leeds from 2010 to 2015 aimed to (1) improve the understanding of key meteorological mechanisms of peak wind generation in dust emission regions (particularly in northern Africa), (2) assess their relative importance, (3) evaluate their representation in models, (4) determine model sensitivities with respect to resolution and model physics, and (5) explore the usefulness of new approaches for model improvements.
The meteorological mechanisms under study included the daytime downward mixing of momentum from nocturnal low-level jets (NLLJs), cold surface outflows from convective storms (haboobs), low-pressure systems (cyclones and depressions), high-pressure systems (harmattan surges) and small-scale dust devils and plumes in the daytime boundary layer. Desert Storms undertook (A) a detailed analysis of observations including station data, measurements from field campaigns, analysis data and novel satellite products, (B) a comprehensive comparison between output from a wide range of global and regional dust models, and (C) extensive sensitivity studies with regional and large-eddy simulation models in realistic and idealised set-ups. In contrast to previous studies, all evaluations were made on a process level concentrating on the specific meteorological phenomena listed above.
The most significant findings from Desert Storms are: (1) The morning breakdown of NLLJs is an important emission mechanism, but details depend crucially on nighttime stability, which is often badly handled by models. (2) Convective cold pools are a key control on summertime dust emission over northern Africa, directly and through their influence on the heat low; they are severely misrepresented by models using parameterized convection. A new scheme based on downdraft mass flux has been developed that can mitigate this problem. (3) Mobile cyclones make a relatively unimportant contribution, except for northeastern Africa in spring. (4) A new global climatology of dust devils identifies local hotspots but suggests a minor contribution to the global dust budget in contrast to previous studies. A new dust-devil parameterization based on data from large-eddy simulations has been developed. (5) The lack of sufficient observations and misrepresentation of physical processes lead to a considerable uncertainty and biases in (re)analysis products. (6) Variations in vegetation-related surface roughness create small-scale wind variability and support long-term dust trends in semi-arid areas.
The results obtain in the Desert Storms project have substantially advanced our quantitative understanding of the global dust cycle and therefore help to reduce uncertainties in predicting climate, weather and many dust-related impacts such as air quality or atmospheric turbidity.
The Desert Storms project funded by the European Research Council and led by Peter Knippertz at the Karlsruhe Institute of Technology and by John Marsham at the University of Leeds from 2010 to 2015 aimed to (1) improve the understanding of key meteorological mechanisms of peak wind generation in dust emission regions (particularly in northern Africa), (2) assess their relative importance, (3) evaluate their representation in models, (4) determine model sensitivities with respect to resolution and model physics, and (5) explore the usefulness of new approaches for model improvements.
The meteorological mechanisms under study included the daytime downward mixing of momentum from nocturnal low-level jets (NLLJs), cold surface outflows from convective storms (haboobs), low-pressure systems (cyclones and depressions), high-pressure systems (harmattan surges) and small-scale dust devils and plumes in the daytime boundary layer. Desert Storms undertook (A) a detailed analysis of observations including station data, measurements from field campaigns, analysis data and novel satellite products, (B) a comprehensive comparison between output from a wide range of global and regional dust models, and (C) extensive sensitivity studies with regional and large-eddy simulation models in realistic and idealised set-ups. In contrast to previous studies, all evaluations were made on a process level concentrating on the specific meteorological phenomena listed above.
The most significant findings from Desert Storms are: (1) The morning breakdown of NLLJs is an important emission mechanism, but details depend crucially on nighttime stability, which is often badly handled by models. (2) Convective cold pools are a key control on summertime dust emission over northern Africa, directly and through their influence on the heat low; they are severely misrepresented by models using parameterized convection. A new scheme based on downdraft mass flux has been developed that can mitigate this problem. (3) Mobile cyclones make a relatively unimportant contribution, except for northeastern Africa in spring. (4) A new global climatology of dust devils identifies local hotspots but suggests a minor contribution to the global dust budget in contrast to previous studies. A new dust-devil parameterization based on data from large-eddy simulations has been developed. (5) The lack of sufficient observations and misrepresentation of physical processes lead to a considerable uncertainty and biases in (re)analysis products. (6) Variations in vegetation-related surface roughness create small-scale wind variability and support long-term dust trends in semi-arid areas.
The results obtain in the Desert Storms project have substantially advanced our quantitative understanding of the global dust cycle and therefore help to reduce uncertainties in predicting climate, weather and many dust-related impacts such as air quality or atmospheric turbidity.