The structure of Southern Hemisphere tropospheric zonal flow in climate model simulations

The spatial structure and temporal evolution of zonal wind in the upper troposphere are analyzed for the complete set of climate model simulations from CMIP3. For the Southern Hemisphere, the simulated tropospheric zonal-mean zonal wind exhibits a wide range of behavior, from single-jet to double-jet and anything in between. This inter-model variation exists in both the 20th century climatology and greenhouse-gas induced trend of the zonal mean flow. The relations among the climatological zonal jets, their trend, and sea surface temperature in the climate model simulations are analyzed to help understand the difference among the models. The multi-model ensemble mean is not representative of the behavior of zonal jets in individual models. This has implications for interpreting the IPCC-type climate projection constructed from multi-model ensemble averaging, for instance concerning the projected pole shift of storm tracks in the warming world.