LAUSR

Abstract This study describes how climatic conditions affect of the generation and transport of dust over the SW Sahara Desert (12°-22°N, 18°W-20°E), with a focus on early summer in the period 1980–2014. Results are given for the annual cycle and climatology of May–Aug season, trends in aerosol optical depth (AOD) and contributing factors, co-variability of monthly and daily AOD and climate variables, case studies of dust generation in early summer and analysis of diurnal fluxes. The study is underpinned by multi-satellite measured AOD and ECMWF meteorological reanalysis fields. Linear trends in the period 1980–2014 indicate that AOD (dust) diminished slightly as rainfall and vegetation cover increased. Concommitant climatic trends include a weakening of Atlantic trade winds, acceleration of the easterly jet and inland penetration of the Guinea monsoon. Trends in temperature and winds strengthen above the boundary layer; suggesting that surface changes are damped by greening of the Sahel 1980–2014. Climatic conditions favoring dust emissions are evident in sensible heat flux, maximum temperature and upward motion at seasonal and daily time scales, with influence from wind vorticity at diurnal time scale. Incremental knowledge on climatic controls of dust mobilization could improve emission budgets and forecasts for the SW Sahara Desert.