Synergy of active and passive airborne observations for heating rates calculation during the AEROCLO-SA field campaign in Namibia

Abstract. Aerosols have important effects on both local and global climate, as well as on clouds and precipitations. We present some original results of the airborne AErosol RadiatiOn and CLOud in Southern Africa (AEROCLO-sA) field campaign led in Namibia in August and September 2017. In order to quantify the aerosols radiative impact on the Namibian regional radiative budget, we use an innovative approach that combines the OSIRIS polarimeter and lidar data to derive heating rate of the aerosols. To calculate this parameter, we use a radiative transfer code and meteorological parameters provided by dropsondes. This approach is evaluated during massive transports of biomass burning particles above clouds. We present vertical profiles of heating rates computed in the solar and thermal parts of the spectrum. Our results indicated strong positive heating rate values retrieved above clouds due to aerosols, between +2 and +5 Kelvin per day (vertically averaged). Within the smoke layer, water vapor's cooling effect through infrared radiation generally balances its warming effect from solar radiation. At the top of the layer, a stronger cooling effect of −1.5 K/day often dominates due to water vapor. In order to validate this methodology, we use irradiance measurements acquired during sounding performed with the aircraft during dedicated parts of the flights, which provides direct measurements of irradiances distribution and heating rates in function of the altitude. Finally, we discuss the possibility to apply this method to available and future spaceborne passive and active sensors.