Seasonal Analysis of Aerosol Frequency and Assessment of the Radiative Impact of a Dust Episode in Burkina Faso, West Africa

Abstract

This work is a contribution to the optical and radiative characterization of aerosols, with the aim of showing the impact of season on the frequency of typical days defined by aerosol optical depth (AOD) and then quantifying the impact of aerosols on incident radiation. The study is based on MODIS sensor observations and in situ measurements, followed by HYSPLIT and streamer model simulations. To this end, a seasonal analysis of AOD indicates a majority frequency of mixed days. These days are heavily dominated by standard days, identified by a maximum frequency centered around an AOD value, depending on climate zone and season. However, dusty days defined by AOD values above 0.8 are due to pulses of mineral particles from emission sources located in the Sahara and the associated atmospheric circulation during harmattan or monsoon periods. Thus, a simulation of the radiative impact of a dust event associated with AOD values observed around 3.09, 1.75 and 1.41 respectively at the Ouagadougou, Dori and Gaoua sites highlights a modification of the solar radiation incident by the aerosol layer. This extinction of solar energy is reflected in an increase in diffuse flux during the dust event, which varies from 41.20 W/m2 to 136.92 W/m2 compared with the days before and after the dust episode. At the same time, a reduction in normal direct flux of between 78.60 W/m2 and 259.64 W/m2 is achieved. This highlights the diffusive nature of the aerosol population specific to desert dust, and its direct radiative impact.