Nonlinear responses of the South Asian High to the Asian tropopause aerosol layer in summer

The Asian tropopause aerosol layer (ATAL) causes significant regional radiative forcing which may influence the tropospheric weather and climate. Our analysis reveals that the intensified ATAL weakens the South Asian High (SAH) and the South Asian Monsoon. The ATAL leads to increases in diabatic heating in the upper troposphere in the SAH region, induces an anomalous upward flow which decreases the adiabatic heating and causes cooling anomalies in the upper troposphere in the SAH region, and ultimately weakens the SAH (diabatic heating mechanism). However, responses of the SAH to the ATAL are nonlinear. Model results indicate that when the ATAL intensity is doubled, a temperature inversion occurs in the upper troposphere which tends to stabilize the upper troposphere and lower stratosphere (UTLS) and prevent the upward moisture transport (static stability mechanism). The reduced latent heat release induces middle and upper tropospheric cooling in the SAH region, thereby weakens the SAH.