Isolating Large-Scale Smoke Impacts on Cloud and Precipitation Processes Over the Amazon With Convection Permitting Resolution

Absorbing aerosol from biomass burning impacts the hydrological cycle and radiation fluxes both directly and indirectly via modifications to convective processes and cloud development. Using the ICOsahedral Non-hydrostatic modelling framework in a regional configuration with 1,500 m convection-permitting resolution, we isolate the response of the Amazonian atmosphere to biomass burning smoke via enhanced cloud droplet number concentrations N_d (aerosol-cloud interactions; ACI) and changes to radiative fluxes (aerosol-radiation interactions; ARI) over a period of 8 days. We decompose ARI into contributions from reduced shortwave radiation and localized heating of the smoke. We show ARI influences the formation and development of convective cells: surface cooling below the smoke drives suppression of convection that increases with smoke optical depth, while the elevated heating promotes initial suppression and subsequent intensification of convection overnight; a corresponding diurnal response (repeating temporal response day-after-day) from high precipitation rates is shown. Enhanced N_d (ACI) perturbs the bulk cloud properties and suppresses low-to-moderate precipitation rates. Both ACI and ARI result in enhanced high-altitude ice clouds that have a strong positive longwave radiative effect. Changes to low-cloud coverage (ARI) and albedo (ACI) drive an overall negative shortwave radiative effect, that slowly increases in magnitude due to a moistening of the boundary layer. The overall net radiative effect is dominated by the enhanced high-altitude clouds, and is sensitive to the plume longevity. The considerable diurnal responses that we simulate cannot be observed by polar orbiting satellites widely used in previous work, highlighting the potential of geostationary satellites to observe large-scale impacts of aerosols on clouds.