An extensive analysis of quasi 5‐day waves (5DWs) in the mesosphere and lower thermosphere and their responses to a major sudden stratospheric warming (SSW) event (January 2013) are presented. The analysis is based on data conducted from a meteor radar chain in the period from December 2008 to November 2017 and Aura Microwave Limb Sounder satellite. The radar chain includes three 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 5DWs present clear interannual and seasonal variations, which are observed by both the radar wind data and Aura‐temperature data. Interestingly, the ter‐annual oscillation is found to be as important as the commonly recognized annual oscillation and semiannual oscillation at the three stations in both neutral wind components. The 5DWs are strong mainly during the August/September in the meridional component, while they are primarily enhanced in the period of January, April/May, and late summer in the zonal component. An enhancement of 5DWs is observed during the 2013 SSW event in the mesosphere and lower thermosphere region at the three stations. The amplitudes during the SSW are more than 2 times larger than the January average. The strength of the amplification is most prominent at MH and reduces as latitude decreases. According to the results obtained from the radar wind and Aura temperature, the enhanced 5DW modes are W1 at MH, and W2 at BJ and WH. Our results indicate that the amplification of the 5DWs is very likely associated with the 2013 SSW.

We present a study of the quasi 10‐day waves (Q10DWs) in the mesosphere and lower thermosphere (MLT) during a sudden stratospheric warming (SSW) event in February 2018 based on three meteor radars located at Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), and Wuhan (WH, 30.5°N, 116.6°E). The enhanced Q10DWs are observed in the meridional component at MH and in the zonal component at BJ and WH. In the meridional component, the monthly mean Q10DW amplitudes in February 2018 are greater than 10 m/s at MH but weaker than ∼7 m/s at BJ and WH. In the zonal component, monthly mean Q10DWs amplitudes are ∼15 m/s at BJ and WH but only 9 m/s at MH. These latitudinal differences of the Q10DWs in the MLT region are very likely due to the Q10DW activity in the lower atmosphere and the mean background winds. The strong southward winds might bring the wave energy to MH in the meridional component during the occurrence of SSW, while the enhanced Q10DWs in the zonal component at BJ and WH are likely associated with the strong Q10DWs in the lower atmosphere and weakening eastward winds after the central date of the SSW. The significance test indicates that the enhanced Q10DWs in the meridional wind of MH and in the zonal wind of WH are very likely affected by the SSW. In addition, nonlinear interactions between the Q10DWs and other planetary waves also modulate the variations in the MLT region at BJ during the SSW.

The Sounding of the Atmosphere using Broadband Emission Radiometry satellite instrument has been measuring the mesospheric global temperature since February 2002, providing the longest continuous data set to statistically study the climatology and anomaly of the quasi‐two‐day waves (QTDWs), including the westward zonal wave number 2 (W2), 3 (W3), and 4 (W4) modes. It is found that the W2 QTDW generally peaks earliest, followed by the W3 mode with the W4 QTDW being amplified lastly. This temporal pattern is always disordered during the sudden stratospheric warming (SSW) periods. The temperature oscillations of the QTDW usually peak at nearly the same period at different altitudes and different latitudes for a certain case but would be different from year to year. The statistical results show that the periods of the W2 QTDWs are more frequently observed to be at 45–48 hr and the periods of the W3 mode are mostly confined between 45 and 52 hr. Nevertheless, the oscillations of the W4 QTDW peak more dispersedly between 41 and 56 hr. The W3 QTDW is usually the strongest among the three modes, whereas it is sometimes equal to or even weaker than W2 and W4 QTDWs, especially during SSW periods. Besides, we found that the vertical distribution of the W3 QTDW splits into a bimodal structure during the SSW periods of 2006 and 2011. And the solar cycle trend of the QTDWs is frequently disturbed by a 2‐ to 5‐year variability, which seems to be a common feature for all the QTDW modes.

We present an analysis of planetary‐scale oscillations during sudden stratospheric warming (SSW) events based on data obtained from a meteor radar located at Mohe (MH, 53.5°N, 122.3°E), the Aura satellite and Modern‐Era Retrospective analysis for Research and Applications, Version 2 data (MERRA2). The planetary‐scale oscillations in the mesosphere and lower thermosphere (MLT) region during eight SSW events from 2012 to 2019 have been statistically investigated. Our analysis reveals that the enhancement or the generation of westward propagating quasi 16‐day oscillation with wavenumber 1 (W1) is a common feature during SSWs over MH. A strong enhancement of the quasi 4‐day oscillation during the 2018/2019 SSW is captured by both radar and satellite observations. The amplified quasi 4‐day oscillation has a period of ~4.3 days in both meridional and zonal winds and with a wavenumber of W2 in the zonal component. Using the meteor radar and MERRA2 data, the vertical structure of the quasi 4‐day oscillation from the stratosphere to the lower thermosphere is derived. The upward propagating feature of the quasi 4‐day oscillation in the meridional component indicates that the oscillation is very likely generated in the lower mesosphere. The mesospheric zonal wind reversal after an elevated stratopause event is observed during the SSW, which results in a negative meridional gradient of the quasi‐geostrophic potential vorticity. Our results not only reveal that the amplified quasi 4‐day oscillation in the MLT region is associated with the 2018/2019 SSW but also suggest that the amplification is originally generated around 60 km due to barotropic/baroclinic instability and propagates upward to MLT region.

This study presents an analysis of the long‐term variations of four propagating quasi 16‐day waves with Wavenumbers 1 and 2 and investigates their association with sudden stratospheric warming (SSW) events. The study is based on the data obtained from Aura Microwave Limb Sounder satellite and Modern‐Era Retrospective Analysis for Research and Applications‐2 reanalysis data in the period from 2004 to 2018. Strong quasi 16‐day waves are found in the winter hemisphere. The propagating waves with Wavenumber 1 are prominent in the Northern Hemisphere and eastward‐propagating waves are dominant in the Southern Hemisphere. By analyzing 14 SSW events, we found that the westward‐propagating quasi 16‐day waves increase rapidly around the onset dates of the major SSWs, which is likely associated with the quickly reduced mean eastward background winds. Based on analysis of geopotential height, Ertel potential vorticity and Eliassen‐Palm flux, the propagating quasi 16‐day waves with Wavenumbers 1 and 2, (mainly from westward‐propagating components) contribute to the formation of the vortex displaced and vortex split SSWs, respectively.

The variability in turbulence is a crucial topic in the lower atmosphere. This study aims to validate the credibility of Thorpe analysis in the statistical study of atmospheric turbulence by applying this method on high‐resolution radiosonde data that are a composite of seven sites at midlatitudes from January 2012 to December 2016. The spatiotemporal variability of turbulent energy dissipation rate is also addressed from 2.4 to 30 km, thereby exhibiting remarkable spatial inhomogeneities and well‐defined seasonal variations. If the ratio between Ozmidov and Thorpe lengths (i.e., c²) is a lognormal distribution, then energy dissipation rate can be simulated by the Monte Carlo method. The approximate proportionalities between the energy dissipation rates revealed by a constant c² and a lognormally distributed c² that is based on the results from Schneider et al. (2015) exist at middle, low, and high latitudes. At midlatitudes, energy dissipation rates by the simulated cases are quantitatively consistent with the radar results. These results suggest that, even for a highly variable c², the Thorpe analysis can be statistically applied to the stably stratified free atmosphere, and the optimal value of c² is 0.54 at all heights and latitudes. We also speculate that the statistical application of a Thorpe sort is acceptable when c² simply follows a lognormal distribution.