Variability and combination as ensemble of mineral dust forecast during the 2021 CADDIWA experiment

Abstract. As an operational support to the CADDIWA field campaign, the coupled regional model WRF-CHIMERE is deployed in forecast mode during the summer 2021. The simulation domain covers West Africa and the East Atlantic and allows the modeling of dust emissions and their transport to the Atlantic. On this route, we find Cape Verde which was used as a base for measurements during the CADDIWA campaign. The forecast consists of meteorological variables and mineral dust concentrations on a horizontal grid with a resolution of 30 km and from the surface to 200 hPa. Each day, the simulation starts the day before (D-1) and up to four days ahead (D+4). For each day, we thus have six different calculations, with logically a better precision the closer we get to the analysis (D-1). In this study, a quantification of the forecast variability of wind, temperature, precipitations and mineral dust concentrations according to the modelled lead is presented. It has been shown that the forecast quality doesn't decrease with time and that high variability on some days for some variables (wind, temperature) does not explain the behavior of other dependent and downwind variables (mineral dust concentrations). A new hypothesis is also tested: why not consider the several six forecast leads available for each date as members of an ensemble forecast? It has been shown that this new forecast, the mean of all forecast leads, is able to give better results for two AERONET stations on the four available for Aerosol Optical Depth. This could open the door to further testing with more complex operational systems.