Contraction of the world’s storm-cloud zones and the relationship to atmospheric circulation changes

We analyze the CERES solar radiative balance trends of the past 23 years, with the objective to separate the contribution to the solar absorption trends of shifts in the atmospheric general circulation and changes in cloud controlling processes. Regimes of large cloud cover and strong cloud radiative cooling are defined in the low latitude and the high latitude zones, representing the tropical rainy zone and the midlatitude storm zones respectively, and the trends in the areal coverage of those regimes over the past 23 years are examined along with the trends in the cloud solar radiative effect within each regime. This allows the decomposition of the global solar cloud radiative trends into circulation induced changes and those induced by cloud controlling processes. The results show that the general circulation component of the cloud solar radiative changes, which manifests itself as a contraction of the midlatitude storm zones and the tropical rainy zone, is the largest term in the solar absorption trend, causing decreased sunlight reflection of 0.37 W/m² per decade. We explore the relationship between the cloud regime contraction and the main atmospheric circulation indices, including the width of the Hadley circulation and the location of the midlatitude jet, in order to understand the processes responsible for the cloud regime changes.