Dynamical and Radiative Influence on the Hadley Circulation by Aerosol‐Cloud Interactions

Abstract How aerosols modulate large‐scale circulation and the cloud radiative effect (CRE) is explored using a two‐dimensional Hadley circulation model with near‐large eddy simulation resolution. Six 30‐day simulations are performed under three aerosol loadings with a prescribed sea surface temperature (SST 0 ) or slab ocean model (SOM). These simulations produce various clouds, although stratocumulus are underrepresented. Aerosol perturbations intensify large‐scale circulation and brighten clouds, as previously reported, although the effect is weaker under SOM. Hadley circulation intensification from a large aerosol perturbation in the subsidence region is linked to radiative‐dynamical adjustments of the shallow meridional circulation driven by enhanced reflectance of shallow clouds. The CRE response to aerosol perturbations is driven by changes in cloud water path (CWP) and cloud fraction ( f c ), with the contribution from droplet number concentration ( N d ) similar to those from CWP and f c under SST 0 but reduced under SOM. The CRE response is dominated by the deep convection region, where aerosol effects amplify CRE along with a slight increase in f c for SST 0 , whereas under SOM, the weaker aerosol effect coincides with a slight decrease in f c . In the subsidence region, CRE enhancement diminishes at high aerosol concentrations, likely due to a negative microphysical‐dynamical feedback identified in shallow clouds. Causal inference analysis applied to the deep convection region reveals that the f c response to N d differs between SST treatments at high aerosol loadings, leading to a muted CRE response under SOM. These results suggest that the Hadley circulation moderates aerosol effects under a dynamically coupled atmosphere‐ocean system.