Solar Experiments with Tropical Cyclone-Permitting GCMs

The response of the climate system, and tropical cyclone (TC) activity in particular, to changes in CO2 and solar radiation are explored in a high spatial resolution general circulation model (GCM) that explicitly simulates TCs. It is found that, after normalizing by global-mean surface temperature change, reductions in the strength of insolation are about twice as effective at modifying globally-integrated TC activity than are increases in CO2 concentrations. However, there are regions in the globe where TC activity changes induced by CO2 increases are not compensated by solar reductions. The mechanisms behind these TC changes are explored. Additional experiments with forcing that is not meridionally symmetric show that the spatial structure of solar forcing can have a fundamental impact on the response of TC activity. Forcing that acts to reduce top of atmosphere radiation preferentially in one hemisphere tends to decrease TC activity in that hemisphere, but enhance it in the opposite one.