Abstract
This paper presents a study using in situ measurements (AERONET data) to characterize the intra-seasonal variability of aerosols and their shortwave radiative impacts on Sahel (11N - 18N and 20W - 15E) climate using a long time series (2000 to 2010) from AERONET data. We first used the MISR aerosol optical depth (AOD) averaged between 2000 and 2010 to identify dust maxima regions. They are mainly located over Eastern Mauritania-Northern Mali and Eastern Niger-Western Tchad (near the Bodele depression). Moreover the aerosol loading is stronger during the spring (MAM) and particularly during the summer (JJA). The analysis of AERONET data at 4 Sahelian stations (Dakar, Agoufou, Banizoumbou and Ouagadougou) shows that Sahel is under dust influence all year long. The dust season is mainly located between March and October, with two peaks of AOD recorded in March and June; while the maximum of biomass burning activity is recorded in winter (December to February). The radiative forcing of aerosols on the Sahelian climate results mainly in a cooling as well as at the surface than at the top of the atmosphere (TOA) but the forcing is stronger at the surface and particularly during the summer (JJA) and spring (MAM) periods. Although there is not a sharp difference between DJF and SON periods from a station to another one when considering the aerosol loading (AOD), the radiative forcing is stronger at the surface and weaker at the TOA during DJF for most stations. The analysis of the force effectiveness (ratio between AOD and the radiative forcing) suggests that the BOA radiative forcing is mainly influenced by the nature of aerosols.
Highlights
West Africa is the biggest dust and biomass burning smoke aerosol source of the world [1,2]
During maxima are recorded in spring (MAM), a maximum is found off the West Africa which results from the low-levels transport by the Harmattan Winds
This study dealt with the characterization of West African aerosols properties and their impacts on the climate using a long temporal series of observations (AERONET data from 2000 to 2010)
Summary
West Africa is the biggest dust and biomass burning smoke aerosol source of the world [1,2]. Massive dust plumes regularly propagate from the continent to the ocean and as far as Florida during the summer in the so-called Saharan air Layer [3,4]. These mineral particles exert a strong influence on the radiative balance and the climate [5,6]. During the winter time, mixed particles composed of dust and biomasses burning are found by [13] The properties of this mixture are very poorly documented [14,15]
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