9:30 AM - 9:45 AM
[AAS09-03] Analysis of Extremely Strong Easterly Wind Events around the stratopause in the Northern Hemisphere winter
Keywords:Extremely strong easterly wind event, Sudden stratospheric warming, Planetary wave-packet propagation, Three-dimensional wave activity flux
We have been investigating the characteristics of atmospheric fields during a major sudden stratospheric warming (MSSW) event occurring in January 2021 (MSSW21) by the use of the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q, Kosaka et al. in preparation). Three-dimensional analysis of planetary-scale wave packets was performed based on the three-dimensional wave activity flux (3D-flux-W, Kinoshita and Sato 2013; Sato et al. 2013; Harada et al. 2019). MSSW21 is characterized by strong easterlies over 70 m s-1 around the stratopause in early January 2021, a mixed signature of wavenumber 1 (WN1), WN2 and WN3 planetary waves, and repetition of polar vortex splitting.
In this study, we investigate the occurrence frequency of such extremely strong easterly wind (ESEW) events over the past 40+ years and the propagation of planetary scale wave packets during ESEW events. In addition to JRA-3Q, we use the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2, Gelaro et al. 2017). The sampling period for ESEW events is 43 years, from January 1980 to December 2022. The event is defined as a daily zonal-mean zonal wind which is easterly with the magnitude exceeding 70 m/s at either JRA-3Q or MERRA-2 grid points in the Northern Hemisphere north of 60° and in the region from 10 hPa to 0.3 hPa.
As an early result, we found that the ESEW event occurred six other times in addition to MSSW 21: February 1980, January 1985, January 1987, January 2006, January 2012, and January 2013. It is interesting to note that these events are concentrated in the 1980's and after 2000. One of the characteristics of these events is that rapid westerly deceleration (easterly acceleration) occurred within a few days (except for the January 2006 event). The January 1985 event in particular shows a rapid change from 60 m s-1 westerly winds to 90 m s-1 easterly winds at the 0.7-hPa level, which means that a westerly deceleration of 150 m s-1 occurs within a few days.
On the day of the meeting, common features and differences will be presented based on the results of analysis of planetary-scale wave packet propagation observed during each ESEW event.
In this study, we investigate the occurrence frequency of such extremely strong easterly wind (ESEW) events over the past 40+ years and the propagation of planetary scale wave packets during ESEW events. In addition to JRA-3Q, we use the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2, Gelaro et al. 2017). The sampling period for ESEW events is 43 years, from January 1980 to December 2022. The event is defined as a daily zonal-mean zonal wind which is easterly with the magnitude exceeding 70 m/s at either JRA-3Q or MERRA-2 grid points in the Northern Hemisphere north of 60° and in the region from 10 hPa to 0.3 hPa.
As an early result, we found that the ESEW event occurred six other times in addition to MSSW 21: February 1980, January 1985, January 1987, January 2006, January 2012, and January 2013. It is interesting to note that these events are concentrated in the 1980's and after 2000. One of the characteristics of these events is that rapid westerly deceleration (easterly acceleration) occurred within a few days (except for the January 2006 event). The January 1985 event in particular shows a rapid change from 60 m s-1 westerly winds to 90 m s-1 easterly winds at the 0.7-hPa level, which means that a westerly deceleration of 150 m s-1 occurs within a few days.
On the day of the meeting, common features and differences will be presented based on the results of analysis of planetary-scale wave packet propagation observed during each ESEW event.