Aerosol Direct Radiative Effects From Extreme Fire Events in Australia, California and Siberia Occurring in 2019–2020

This study aims at investigating the biomass burning aerosols (BBA) from 2019 to 2020 extreme wildfires in California, Australia and Siberia, in terms of aerosol characteristics and direct radiative effect. This study is based on the comparison between global climate simulations (ARPEGE-Climat) and reference aerosol data sets (reanalyzes, ground-based observations and satellite data). First, our results demonstrate the need to constrain the injection heights in the model in order to realistically represent extinction vertical profiles observed during fire events, both in the troposphere and in the lower stratosphere due to the contribution of pyro-convection. Without specific vertical emission profiles for fires, the ARPEGE-Climat simulations fail in representing aerosol extinction vertical profiles. For each region studied, the modeled aerosol optical depth (AOD) is extremely high (above 3 at 550 nm). An important long-range transport of BBA emitted in Australia and California is shown, with high AOD further from sources. These extremely dense plumes significantly perturb the surface incident solar radiation and exert a large direct (surface) shortwave radiative effect up to −13, −29 and −17 W $m^{-2}$ on monthly average over Australia (January 2020), California (September 2020) and Siberia (August 2019), respectively. A noteworthy positive BBA direct radiative effect (warming) is found at the top of the atmosphere, when dense and strongly absorbing smoke plumes are advected over cloudy oceanic regions, characterized by high surface albedo. This absorption leads to an increase of the solar heating rate up to 0.3 K ${\text{day}}^{-1}$ with possible implications on the atmospheric temperature and dynamics.