The Study Of Sodium Seasonal Variations And Tidal Wave Activities In Winter Over Beijing

Based on the basic equation of lidar,the calculation of the effective backscatter cross section and the derivation of normalization are presented detailedly,moreover,the retrieval method of sodium density is showed simultaneously.Sodium is a good tracer of atmospheric fluctuations,which can contribute to the in-depth study all kinds of complex dynamic and chemical processes in the mesopause region.Based on observation data,the research of sodium seasonal variation and the study of tidal characters by continuous sodium observation data can be proceeded.The data from 2013 to 2017,which including 103 nights and involving 1101.5hours,is the base of the study of sodium annual variation.In order to enhance signal to noise ratio and reduce error,the data is combined and processed by moving average method.The observation results reveal nocturnal annual mean column density of the sodium layer is 1.141×10⁹cm^-2,the mean centroid height is 91.1km,the mean RMS width is 4.7km.Sodium layer shows considerable annual variation with minimum in summer and maxima in winter.Column density presents prominent annual variation,which reaches maxima in winter and minimum in summer.The centroid height and RMS widths behave semiannual variation.The central height shows maxima in spring and autumn and minimum in summer and winter,the result of RMS width is opposite.The results in Beijing are similar to that in other lidar sites.However,the minimum column density is 0.3518×10⁹cm^-2,which makes the ratio between maxima and minimum of column density is 23,that is larger than other observation results.Because of the interference of sunlight,lidar observation only carries at night.Observing sodium layer in the daytime realize by adding a Faraday atomic vapor filter.Based on continuous observation of sodium layer from lidar located in Yanqing,Beijing,the diurnal variation of the sodium layer and its relevant parameters can be analyzed.Comparing the phase information of sodium density from every altitude with the information from meridian wind at the same time,we can find the two diurnal phases can be consistent with each other.Although the two semi-diurnal phases exist a little bit difference,as a whole,they two agree very well.Extracting the phase and amplitude from continuous sodium observation data from October to January during 2014 to 2016,tidal characters in winter over Beijing can be studied.The results shows:diurnal tide phases have unobvious seasonal variation and propagate upward with vertical wavelengths between 40 and 50 km.Besides,the diurnal tide is stronger than semidiurnal tide.