Direct Responses of the Tropical Circulation and Tropical Cyclones to Radiative Forcing Agents

It is well established that anthropogenic radiative forcing agents, such as carbon dioxide, affect the surface temperature by altering Earth's radiation balance. Recent research has exposed that radiative forcing agents can also directly affect the tropical atmosphere, even in the absence of surface temperature changes. Here, we assess the extent to which different radiative forcing agents---carbon dioxide and solar forcing---have distinctive direct responses in the tropical atmosphere. First, we show that atmospheric general circulation models (GCMs) have distinct direct changes in the strength of the Hadley circulation between forcing agents. Second, we show that tropical cyclone-permitting, high resolution GCMs have distinct direct changes in the global number of tropical cyclones. These tropical cyclone changes are consistent with the simulated changes in the mean circulation and thermodynamic factors. These results can be understood by considering the moist energetics of the mean tropical circulation.