Assessing the destructiveness of tropical cyclone by anthropogenic aerosols under an atmosphere-ocean coupled framework

Abstract. Tropical cyclones (TCs) with a high Saffir-Simpson scale can cause catastrophic damages to coastal regions after landfall. Recent studies have linked the TC’s devastation to climate change that induces favorable environmental conditions, such as increasing sea-surface temperature, to supercharge the storms. Also, atmospheric aerosols likely impact the development and intensity of TCs, but their effects remain poorly understood, particularly coupled with the ocean dynamics. Here we quantitatively assess the aerosol microphysical effects and aerosol-modified ocean feedbacks during Hurricane Katrina using a cloud-resolving atmosphere-ocean coupled model - Weather Research and Forecasting (WRF) in conjunction with the Regional Ocean Model System (ROMS). Our model simulations reveal that an enhanced destructive power of the storm, as reflected by larger integrated kinetic energy, heavier precipitation, and higher sea-level rise, is linked to the combined effects of aerosols and ocean feedbacks. These effects further result in an expansion of the storm circulation with a reduced intensity because of decreasing moist static energy supply and enhancing vorticity Rossby wave outward propagation. Both accumulated precipitation and storm surge are enhanced during the mature stage with elevated aerosol concentrations, implying exacerbated flooding damage over the coastal region. The ocean feedback following the aerosol microphysical effects tends to mitigate the Ekman upwelling cooling and offsets the aerosol-induced storm weakening, by invigorating cloud and precipitation near the eyewall region. Our results highlight the importance of accounting for the effects of aerosol microphysics and ocean-coupling feedbacks to improve the forecast of TC destructiveness, particularly near the heavily polluted coastal regions along the Gulf of Mexico.