资源环境科技发展态势分析平台

Observational features of atmospheric fields during a zonal wave number 2-type major sudden stratospheric warming (MSSW) event in February 2018 (MSSW18) are analyzed using the Japanese 55-year Reanalysis, satellite measurements by a microwave limb sounder, and a new three-dimensional wave activity flux. MSSW18 is characterized by a clear polar vortex split, continuance of easterlies with evident double peaks, clear planetary wave propagation in the easterly region of the upper stratosphere and extraordinary upward propagation of wave number 2 planetary waves from the upper troposphere. The upward propagation peak is comparable to that during an MSSW event in January 2009 (MSSW09), although MSSW18 shows relatively modest warming, unclear disappearance of the stratopause and weak stratopause elevation compared to those during MSSW09. Further analyses reveal that wave packets propagates upward simultaneously in both the Eastern and Western Hemispheres. Those observed in the Eastern Hemisphere converge strongly at the western edge of the Aleutian High, and most of them do not propagate further into the upper stratosphere. The wave packets observed in the Western Hemisphere propagate locally into the upper stratosphere over North America despite the fact that easterlies were predominant there in the mature stage of MSSW18. Furthermore, the results of our study reveal that the regions and levels of wave packet attenuation correspond well to the areas that smaller-scale waves have weak eastward phase tilt or are in the quasi-barotropic condition during MSSW18, whereas during MSSW09 the westward phase tilts of smaller-scale waves were clearly visible in the upper stratosphere.

Plain Language Summary A major sudden stratospheric warming (MSSW) event occurred in February 2018 (MSSW18). We analyze observational features of atmospheric fields during MSSW18 using an atmospheric reanalysis and satellite observational data. We also use a new three-dimensional wave activity flux that can represent wave packet propagation accurately. We explore that the clear polar vortex split is observed and easterlies become predominant in the stratosphere. However, the stratospheric temperature warming during MSSW18 is relatively modest compared with that in an MSSW event in January 2009. The modest warming during MSSW18 is related to the suppression of upward planetary wave propagation into the stratosphere. We find that eastward phase tilt or the quasi-barotropic condition of smaller-scale waves (zonal wave number 5 or more) play an important role in this suppression of the upward planetary wave propagation during MSSW18.