Projected changes of stratospheric final warmings in the Northern and Southern Hemispheres by CMIP5/6 models

Using the historical, moderate emission scenario (RCP45/SSP245), and high emission scenario (RCP85/SSP585) experiments provided by the Coupled Model Intercomparison Project Phases 5 and 6 (CMIP5/6), future changes of stratospheric final warming (SFW) events are explored in this study. Most CMIP5/6 models project a delay of SFWs in the two future scenarios, compared with historical simulation in both hemispheres (4–8 days shift in the multimodel mean). The projected delay in SFWs suggest a later seasonal transition from the climatological wintertime to summertime circulation in both hemispheres. In the Southern Hemisphere (SH), essentially all of the delay in the SFW occurs in the era with strong ozone depletion (1980–2040), and the SFW date is largely unchanged as ozone recovers through the end of the century. Both CMIP5 and CMIP6 multimodel ensemble means (MMEs) do not project any significant change in reversal of westerlies and the stratosphere-troposphere coupling strength during the Northern Hemisphere (NH) SFW. In contrast, both CMIP5 and CMIP6 MMEs project a significant decrease in the strength of SH SFW, but the lower tropospheric response to the SH SFW changes little during 1980–2040. However, the near-surface response to SH SFWs is projected to be significantly stronger during 2040–2100 than during 1980–2040, as well as in CMIP6 than in CMIP5. Biases in SFW over the historical period are generally larger in the NH than in the SH, and show little improvement from CMIP5 to CMIP6.