Convective organization, tropical cyclones and climate sensitivity

Using a mesoscale model in a doubly periodic domain with specified SST, it is shown that tropical mean relative humidity, cloud properties and implied climate sensitivity depend strongly on planetary rotation and the development of tropical cyclones in the model domain. Rotation leads to increased surface wind speeds, which speed up the hydrologic cycle and lead to a net increase of atmospheric temperature. Tropical cyclones develop when uniform rotation is set to that of the Earth at 10?N, if the model resolution is sufficient and the ambient vertical wind shear is not too great. The development of a tropical cyclone in the domain causes the precipitation and clouds to be organized by the synoptic and mesoscale flow. Precipitation intensity is increased, convective cloud area is decreased and average relative humidity in the free troposphere is decreased. The net effect of tropical cyclone development is stronger sensitivity of the outgoing longwave radiation to surface temperature. The reduced climate sensitivity implied by the greater sensitivity of OLR to SST is offset by a stronger positive cloud feedback in the model when a cyclone is present, which results primarily from a reduction in reflection of solar radiation by clouds.