Lidar Data Study Of The Upper Boundary Of The Mid-Latitude Sodium Layer

Lidar at an early stage can detect the sodium layer distribution between about 80-105 km in general due to the limitation of detection capability.As the lidar technology continues to mature,researchers have reported many short-term sporadic thermospheric sodium layers above 110 km.However,a series of important scientific issues,such as the long-term phenomenon that can reflect the height range variation of the upper boundary of the sodium layer and its corresponding nighttime evolution,seasonal variation,and influencing factors,have not been adequately studied.Based on this,this thesis analyzes a total of 1589 h of sodium fluorescence lidar data from November 2018 to December 2019 in Yanqing(116.0°E,40.5°N)at a temporal and spatial resolution of 1 h1 km.The main study includes the following two parts:Observation and study of the Yanqing sodium layer: By analyzing the data,the range of heights reachable at the upper boundary of the Yanqing sodium layer,its corresponding seasonal variation and nighttime evolution were obtained.The probabilities of the top sodium layer reaching 110 km,120 km and 130 km are 99.94 %,84.46 % and 40.34 %,respectively,which indicate that the top sodium layer can reach 120 km in most cases,breaking the traditional view that the top sodium layer is at 105 km(or 110 km);the seasonal variation of the upper boundary height range is the highest density in May and June and the lowest density in February and March;the density of the top sodium layer increases in the second half of the night.Correlation analysis: The effects of meteor injection and temperature on the altitude range of the upper boundary altitude range were compared.The characteristics of three thermospheric sodium layers,the dawn thermosphere-ionosphere Na,the low thermospheric sodium layer and the midnight thermosphere-ionosphere Na existing in the Yanqing,and their contributions to the upper boundary were preliminarily analyzed.It is found that only the general increase in sodium density in the second half of the night correlates with the amount of meteor injection at this time;the upper boundary of the sodium layer is relatively low in February and March when the temperature is higher,which is consistent with the conclusion that the atomic layer is not easily formed when the temperature is higher than 120 km;the highest upper boundary is high in May to December when the thermospheric sodium layer is frequent,and relatively low in March when the thermospheric sodium layer is rare.From the analysis of the observations and correlations,we conclude that the thermospheric sodium layer contributes greatly to the expansion of the upper boundary of the sodium layer,followed by meteor injection,and the temperature has the lowest influence.The study of the variation pattern and specific formation mechanism of the thermospheric metal layer above 110 km will enable us to know more about the unique dynamical and chemical processes in this region,and provide a theoretical basis for expanding the detection altitude range of wind and temperature.