Extraordinary quasi-16-day wave activity from October 2013 to January 2014 with radar observations at mid-latitudes and MERRA2 reanalysis data

Abstract

Combining two meteor radar observations at mid-latitudes and MERRA2 reanalysis data, we report an extraordinary quasi-16-day wave (Q16DW) activity in the mesosphere and lower thermosphere (MLT) from about October 2013 to January 2014. The Q16DW is not only active for a long period, but also unrelated to stratospheric sudden warming (SSW), while 7-year radar observations indicate that strong waves and oscillations in the MLT at mid-latitudes occur generally in winter, and are almost always associated with SSW and stratospheric final warming (SFW), except the extraordinary Q16DW. Meanwhile, during the SSW and SFW in February and March 2014, the observation and reanalysis data show that an intense Q16DW arises in the stratosphere but is not present in the MLT. The two Q16DWs are obviously distinguished from each other. The exceptional Q16DW shows a slowly downward phase progression from the MLT to the troposphere with predominant wavenumber 1, while the second Q16DW has a steeper vertical phase in the stratosphere with predominant wavenumber 2. Although the eastward winds prevail, these Q16DWs are weakened and evanescent in the region with the westward wind and negative refractive index. EP flux vector indicates that these waves originate mainly from the lower atmosphere at mid- and high-latitudes, and are intensified in the middle stratosphere. The first Q16DW may make a little contribution to polar vortex intensification due to small EP flux divergence. However, the Q16DW in the SSW has a strong negative divergence almost in the whole polar stratosphere, implying an important role in the stratospheric zonal wind reduction in the SSW. Graphical Abstract: [Figure not available: see fulltext.].