Bias in simulated long-term changes in the Southern Hemisphere climate in CMIP5 models and role of the stratospheric representation.

There is evidence that a better representation of the stratosphere in climate models could lead to improved predictability of the climate system at different timescales. In the Southern Hemisphere (SH), long-term changes associated to the ozone depletion over Antarctica have dominated SH climate change in austral spring and summer over the past few decades. Implications of ozone induced cooling include the strengthening of westerly winds in the stratosphere with a later transition to easterlies, a poleward shift of the jet stream in the troposphere during SH summer and a projection of these long-term changes onto a high-index polarity of the SAM. Recently, it has been proposed that a limited representation of stratospheric processes could lead to a bias in the representation of tropospheric long-term changes in climate model simulations. In this work, CMIP5 models are analysed in order to link long-term changes in the stratosphere, associated to the respesentation of the stratosphere in models, to simulated changes in the tropospheric eddy-driven jet and the associated upper tropospheric Rossby wave breaking. Implications for future scenarios are also discussed.