Estimates of trends in planetary boundary layer height over Europe are presented, based on daily radiosonde observations at 25 stations during 1973–2010 and using a bulk Richardson number approach to determine heights. Most stations show statistically significant increases in daytime heights in all four seasons, but fewer show statistically significant trends in nighttime heights. Daytime height variations show an expected strong negative correlation with surface relative humidity and strong positive correlation with surface temperature at most stations studied, on both year-to-year and day-to-day time scales. Similar relations hold for long-term trends: increasing daytime boundary layer height is associated with decreasing surface relative humidity and increasing surface temperature at most stations. The extent to which these changes are regionally representative or local reflections of environmental changes near the observing stations is difficult to ascertain.

We present an analysis of the responses of quasi 2 day waves (QTDWs) to the 2013 sudden stratosphere warming (SSW) in the mesosphere and lower thermosphere (MLT) region. The study is based on data collected by a meteor radar chain along the 120°E meridian in the Northern Hemisphere which consists of four stations at Mohe (52.5°N, 122.3°E), Beijing (40.3°N, 116.2°E), Wuhan (30.5°N, 114.6°E), and Sanya (18.3°N, 109.6°E). It is the first time that an enhancement of the QTDW in the neutral wind during the 2013 SSW is observed in the midlatitudes in the Northern Hemisphere. During the SSW, the amplification of the QTDW in the low latitudes is the most prominent and the direction of the mean zonal wind shows clear reversion from eastward to westward. The consistent variations of the QTDWs and the mean neutral wind at the four stations are very likely associated with the SSW.

In this paper, we present a study of the low‐latitude field‐aligned irregularities formation and evolution during the 7–8 September 2017 geomagnetic storm by analyzing data of the very high frequency coherent radar installed at Fuke, Hainan Island of China (19.5°N, 109.1°E; magnetic latitude 9.58°N) and a colocated Digisonde Portable Sounder. The prompt penetration of eastward interplanetary electric field associated with sudden southward turning of the interplanetary magnetic field Bz resulted in large ascent of the F layer, making conducive conditions at the bottomside of the layer for the growth of Rayleigh‐Taylor instability and the development of the plasma irregularities in the postsunset hours. The irregularities persisted into the postmidnight sector when the southward interplanetary magnetic field Bz gradually decreased to the quiet time values. In addition, the base height of F layer at Fuke also showed a large elevation after midnight during two consecutive substorm onsets, suggesting that the substorm‐induced overshielding penetration electric field may take over and modify the ambient zonal electric field in low‐latitude ionosphere and induce the irregularities in the postmidnight sector. Moreover, different from the quiet time eastward movement of the irregularities observed over Fuke, the storm time irregularities displayed no zonal drift at the initial period and subsequently began drifting westward. The reversal of background plasma zonal drift velocity observed by Hainan digisonde characterized the storm time zonal drift pattern of the irregularities.

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.