Community Talk: Eun-Pa Lim (Bureau of Meteorology)
CMIP6 evaluation on the dynamical evolution of the SH polar vortex anomalies
Abstract
The springtime stratospheric polar vortex variability over Antarctica is an important source of predictability of the southern annular mode (SAM) and associated southern hemisphere (SH) regional climate in austral spring-summer seasons. The Antarctic spring vortex anomalies often result from the poleward and downward progression of the meridional dipole anomalies of the SH stratospheric winter jet with vigorous wave-mean flow feedback. This dynamical process is conveniently captured by an anti-correlation of the zonal mean zonal wind anomalies at 60°S in the upper stratosphere between winter and spring. In this study, we evaluate the ability of CMIP6 models to simulate the dynamical evolution from the stratospheric winter jet to the spring polar vortex to its downward coupling to the tropospheric SAM. We examine zonal winds from 41 models at all available pressure levels with the historical forcing’s and the future forcing’s following the Shared Socioeconomic Pathway 5-8.5.
Our results show that many models, including ACCESS ESM1.5 and CM2, do not simulate the observed anti-correlation between the winter and spring polar westerlies, and these dynamical evolution biases are linked to the models’ biases in the mean position of the winter stratospheric jet. The identified winter stratospheric jet-spring polar vortex biases appear to affect the models’ future projections of the Antarctic stratospheric vortex and associated SAM with increasing greenhouse gases by the end of the 21st century.
Please use this thread for further discussion on this talk.