Impact of SST Forcing on Atmospheric Temperature Trends and Tropical Cyclone Activity

The role of different SST forcings and different atmospheric models on the ability to simulate historical upper troposphere (UT) and the tropical tropopause layer (TTL) temperatures are explored using the CMIP5 AMIP experiments and the US-CLIVAR Hurricane Working Group AMIP experiments. The impacts of different simulated tropical temperature changes in the UT and TTL on tropical cyclone (TC) activity are also explored. The results using the multi-model ensemble are compared to those of idealized experiments with a high-resolution global model, in which UT and TTL temperatures are changed. It is found that AGCMs forced with the Hadley Center SSTs (used in the US-CLIVAR experiments) tend to show reduced tropospheric warming (per degree surface warming) compared to the AGCMs forced with Hurrel SSTs (used in the CMIP5 experiments). Both UT and lower TTL cooling lead to an overall increase in potential intensity (PI), but modeled impacts on TC frequency changes are somewhat more subtle.