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According to the observational data for over 120 nights of the Rayleigh lidar located in Beijing, China (40.5°N, 116.2°E), the middle atmospheric thermal structure (35–85 km) over North China was obtained. Lidar observation results show good agreements with SABER temperature data sets, which justify that both the two instruments are reliable. Lidar results show significant difference with the NRLMSISE-00 empirical model and lidar temperatures are usually colder than the model data during the observational time, which may be due to the associations of high level of solar activity, greenhouse gases and the frequent haze weather in North China. To characterize the seasonal variations of the atmospheric temperature structure over Beijing, the amplitude and phase profiles of the annual, semi-annual and 3-month sinusoidal oscillations were extracted by multi-parameter sinusoidal regression. A stratospheric temperature enhancement (STE) event and a long-term mesospheric temperature inversion layer (MIL) are observed in the early winter of 2012/2013. The observed STE event could be due to the enhancement of planetary wave ( k =1) activity while the long-term MIL could be due to gravity wave-planetary wave interactions in the masopause region. [ABSTRACT FROM AUTHOR]

Sporadic sodium layers (SSLs) have been observed all over the globe and always has been of great concern. However, most researches on SSLs are based on only nocturnal observations due to strong daytime solar background noise, thus there is still insufficient understanding of the diurnal variation of SSLs. In this paper, a statistical analysis of SSLs observed by a diurnal sodium (Na) lidar at Beijing (40.5 ° N, 116 ° E) from April 2014 to December 2016 has been reported. A total of 54 and 87 events that peaked during daytime and nighttime, respectively, are identified. The average occurrence interval for daytime observations is ~36 h per SSL, which is slightly longer than the value of ~29 h per SSL for nighttime observations. Both daytime and nighttime SSLs show evident seasonal variations with summer SSLs occurring much more frequently and tending to appear at higher altitude with lower peak density while larger strength factor. The seasonal dependence of SSL occurrence is consistent with that of sporadic E (Es) occurrence, however, their diurnal variations are found to be totally different. The SSLs are observed more frequently around 03–04 LT during nighttime and 16–17 LT during daytime when Es layers appear at lower altitudes (below 110 km), while have a lowest occurrence rate around midday when Es layers occurrence rate peak. The average peak altitude of SSLs during the second half of the night is lower compared to that during the first half of the night. Around midday, the average peak width of SSLs is narrower and peak density tends to be smaller when compared to those at other times. The possible explanations for the diurnal and seasonal variations of SSLs characteristics are discussed, and the key role of the evolution of Es layer height modulated by semidiurnal tide in the local time variation of SSL is highlighted. • The occurrence rate of daytime SSLs has a similar seasonal dependence to those of nighttime SSLs as well as Es. • SSLs occurred more frequently around 03–04 LT during nighttime and 16–17 LT during daytime, while rarely around midday. • Both daytime and nighttime observations SSLs tend to have higher peak altitude, larger strength factor, lower peak density in summer. • Diurnal variation of SSL occurrence is related to tidal-modulated Es height and photochemistry and ionization reactions. [ABSTRACT FROM AUTHOR]