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Scholarship Reports
Quantifying the regional effects of Saharan dust outbreaks on the atmosphere and surface energy budget
William T. Morgan
Department of Meteorology, University of Reading, UK
My undergraduate research scholarship was undertaken at the Department of Meteorology at the University of Reading, under the supervision of Dr Eleanor Highwood. The project was aimed at investigating and categorising the effect of Saharan dust outbreaks. The project involved the utilisation of several key skills such as an effective review of related literature, application of satellite and in-situ data, employment of a sophisticated radiative transfer model and scientific report writing and presentation skills. The research was mainly conducted through independent study, with weekly meetings with my supervisor in support of the project. The project was very enjoyable and will certainly be beneficial to my further studies. The enhanced skills acquired through this project will be of substantial benefit when I undertake my forthcoming 3rd year undergraduate project. The opportunity to work within a research environment was enlightening and has greatly influenced my intention to continue my education on a research-orientated course upon completion of my degree.
Saharan dust is capable of substantially influencing the local energy budget either through direct effects, by radiative forcing, or by indirect effects, such as modifying the physical properties of clouds. Deposition of Saharan dust to the Atlantic Ocean affects its biogeochemistry, thus feeding back upon the climate and dust production. This initial study quantifies the frequency, duration and extent of these events as well as providing insights into the effects upon the energy budget and the Atlantic Ocean. This study suggests that peak dust events, which take place during the morning, are a consequence of solar heating. A strong coupling between the production of dust and solar radiation is surmised. The duration of dust events is dependent upon the proximity of a location to high dust source regions. The suspension of dust within the atmospheric column is also controlled by the strength of the wind. Dust transport over the Atlantic Ocean is dependent upon the time of year. During January and February, dust is transported south of the equator. Conversely, during June, July and August, it is transported north of the equator. Sensitivity experiments suggest that an aerosol layer above an ocean surface will result in cooling at the surface and at the top of the atmosphere. Conversely, over a desert surface, an aerosol layer will exert a cooling trend at the surface and a warming tendency at the top of the atmosphere. Changes in the thickness or height of the aerosol layer cause a relatively negligible effect on the radiation balance. Within the Saharan Air Layer (SAL), changes in the distribution of aerosol cause a more pronounced radiative effect than changes outside of the SAL. Dust deposition to the Atlantic Ocean during June, July and August 2004 is estimated at 61Tg, in close agreement with previous studies.
The research presented in the study will form part of a poster to be presented at the AMMA International Conference in Dakar in November 2005. The work could potentially form part of any research forthcoming from the Dust Outflow and Deposition to the Ocean (DODO) campaign due to take place in 2006.