Aerosol radiative effect during the summer 2019 heatwave produced partly by an inter-continental Saharan dust outbreak. 1. Shortwave dust-induced direct impact

Abstract. The shortwave (SW) direct radiative effect during the summer 2019 heatwave produced partly by a moderate, long-lasting Saharan dust outbreak over Europe is analysed in this study. Two European sites (periods) are considered: Barcelona, Spain, (23–30 June) and Leipzig, Germany (29–30 June). Major data are obtained from AERONET and MPLNET observations. Modelling is used to describe the different dust pathways. The dust coarse (Dc) and fine (Df) components (total dust, DD = Dc + Df) are separated in the profiles of the total particle backscatter coefficient using the POLIPHON method in synergy with MPLNET measurements. This information is used to calculate the relative mass loading and the centre-of-mass height, as well as the contribution of each dust mode to the DD radiative effect (DRE). The mean dust optical depth and its Df / DD ratios are, respectively, 0.153 and 24 % in Barcelona and 0.039 and 38 % in Leipzig. The dust produced a cooling effect on the surface with a daily mean DRE (Df / DD DRE ratio) of −9.1 W m⁻² (37 %) in Barcelona and −2.5 W m⁻² (52 %) in Leipzig. Although less intense than on surface, a cooling is also observed at the top-of-the-atmosphere (TOA), where the Df / DD DRE ratio is even though higher (45 % and 60 %, respectively, in Barcelona and Leipzig). Despite the predominance of Dc particles under dusty conditions, the SW radiative impact of Df particles can be comparable to, even higher than, that induced by the Dc ones. In particular, the Df / DD DRE ratio in Barcelona increases by +2.4 % (surface) and +2.9 % (TOA) day⁻¹ along the dusty period. These results are especially relevant for the next ESA EarthCARE mission (planned in 2022), as devoted to aerosol-cloud-radiation interaction research.