How do aerosols impact atmospheric circulation and radiative forcing through deep convection?

Description

Aerosol-cloud interaction is recognized as one of the key factors influencing cloud properties and precipitation regimes. For deep convection clouds (DCCs), latent heat could be significantly changed through aerosol microphysical effects, which could impact large-scale circulation. The study explores the possibilities of changes on large-scale circulation through aerosol microphysical effect by examining how aerosols change horizontal and vertical mass fluxes, latent heat, and radiation fluxes under different wind shear conditions for typical convective clouds (i.e., warm- and cold-based) from the ARM Mobile Facility (AMF) China field campaign and the Southern Great Plains (SGP) intensive operational period (IOP) 2006. Using model simulations from the Weather Research and Forecasting (WRF) model coupled with a spectral-bin microphysics (SBM) and the observational analysis from the long-term data at the SGP site, we demonstrate that large-scale circulation can be dramatically changed by aerosols through modifying latent heat and updraft and downdraft mass fluxes. Under weak wind shear conditions, aerosol microphysical effects invigorate DCC, enhance latent heat release, and increase vertical velocity and subsidence. The effect is particularly significant for warm-based DCC. However, it does not hold anymore when wind shear becomes stronger. For both warm- and cold-based DCC, the changes on latent heat, vertical velocity, and vertical mass fluxes are becoming much smaller. We note that increasing wind shears could change the sign of aerosol impact on convective strength: from the invigorating effect under the weak wind shear to the suppressing effect when wind shear gets stronger, consistent with our previous finding for an isolated DCC case. This finding may significantly enhance our understanding in aerosol-deep convection interactions and provide a scientific basis to better parameterize aerosol effects on convection and large-scale circulation. Therefore, it will have important implications for reducing uncertainties in climate simulations and projection.