EPP

This study presents an analysis of the quasi-16-day wave (Q16DW) at three stations in the middle latitudes by using a meteor radar chain in conjunction with Aura Microwave Limb Sounder temperature data and MERRA2 (Modern-Era Retrospective Analysis for Research and Applications, Version 2) reanalysis data from 2008 to 2017. The radar chain consists of three meteor radar stations located at Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), and Wuhan (WH, 30.5°N, 114.6°E). The Q16DW wave exhibits similar seasonal variation in the neutral wind and temperature, and the Q16DW amplitude is generally strong during winter and weak around summer. The Q16DW at BJ was found to have secondary enhancement around September in the zonal wind, which is rarely reported at similar latitudes. The latitudinal variations of the Q16DW in the neutral wind and temperature are quite different. The Q16DW at BJ is the most prominent in both neutral wind components among the three stations and the Q16DW amplitudes at MH and WH are comparable, whereas the wave amplitude in temperature decreases with decreasing latitude. The quasi-geostrophic refractive index squared at the three stations in the period from 2008 to 2017 was revealed. The results indicate that the Q16DW in the mesosphere and lower thermosphere (MLT) at MH has a limited contribution from the lower atmosphere. Around March and October, the Q16DW in the troposphere at BJ can propagate upward into the MLT region, whereas at WH, the contribution to the Q16DW in the MLT region is largely from the mesosphere.

Using Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data in the northern hemisphere at the 10 hPa level, we compared the stratospheric evolution of temperature and geopotential height during two major sudden stratosphere warming events (SSWs) that occurred in the Arctic winter of 2018 and 2019. In the prewarming period, poleward temperature-enhanced regions were mainly located around 120°E with a displaced vortex and around 120°E and 60°W with splitting vortices. The evolution of geopotential height indicated that these temperature-enhanced regions were both on the western side of high-latitude anticyclones. In the postwarming period, the polar vortex turned from splitting to displacement in the 2018 SSW but from displacement to splitting in the 2019 SSW. Both transitions were observed over the Atlantic region, which may have been caused by anticyclones moving through the polar region. Our findings revealed that the evolution of the anticyclone is important during SSWs and is closely related to temperature-enhanced regions in the prewarming periods and to transitions of the polar vortices in postwarming periods.

Anomalous change of zonal wind quasi-biennial oscillation (QBO) in winter 2015-2016 has received close attention. Combining radiosonde and satellite observations and reanalysis data, we investigate anomalous changes in temperature and ozone QBOs from the lower to middle stratosphere. As wind shear direction is reversed due to unexpected changes of zonal wind QBO at about 24-30 km, the shortest cold phase at 21-27 km appears in temperature QBO, which is different from completely interrupted westward phase in zonal wind QBO, while the longest cold phase above almost 27 km lasts for 2-3 years from 2015 to 2017 owing to the absence of corresponding warm phase. Meridional scale reduction of temperature QBO causes a small temperature anomaly, thus thermal wind relationship looks seemingly different from that in the other regular QBO cycles. QBO in ozone mixing ratio anomaly shows a double-peak with inverse phase, and its phase below (above) 30 km is in agreement with (opposite to) the phase of temperature QBO because of different control mechanisms of ozone. Following temperature QBO variation, QBO in ozone mixing ratio anomaly exhibits a less positive phase at 20-30 km in 2016-2017, and a very long positive phase above 30 km from 2015 to 2017. QBO in total column ozone shows a small peak in winter 2016-2017 since ozone is mainly concentrated at 20 to 30 km. Anomalous changes of temperature and ozone QBOs due to unexcepted QBO zonal wind variation can be well explained according to thermal wind balance and thermodynamic balance.