Interpreting the Dependence of Cloud-Radiative Adjustment on Forcing Agent

Abstract

Effective radiative forcing includes a contribution by rapid adjustments, that is, changes in temperature, water vapor, and clouds that modify the energy budget. Cloud adjustments in particular have been shown to depend strongly on forcing agent. We perform idealized atmospheric heating experiments to demonstrate a relationship between cloud adjustment and the vertical profile of imposed radiative heating: boundary-layer heating causes a positive cloud adjustment (a net downward radiative anomaly), while free-tropospheric heating yields a negative adjustment. This dependence is dominated by the shortwave effect of changes in low clouds. Much of the variation in cloud adjustment among common forcing agents such as (Formula presented.), (Formula presented.), solar forcing, and black carbon is explained by the “characteristic altitude” (i.e., the vertical center-of-mass) of their heating profiles, through its effect on tropospheric stability.