Structures And Interannual Variations Of The Nocturnal Mesospheric Na An Fe Layers At 30°N

Based on the observation data of Na and Fe Lidar of Wuhan University from January 2004 to December 2012,the average characteristics?nighttime and seasonal variations of the mesospheric Na and Fe layers at 30°N during this period are obtained.Considering the influence of the nighttime and seasonal changes of the Na and Fe layers,we extract the inter-annual change(or long-term changes)of the Na and Fe layers,and then the theoretical analysis of the the factors which impact the inter-annual change of metal layers further clarify the physical and chemical mechanisms behind the change of the metal layers.At the same time,we compare and discuss the inter-annual changes of the metal Na layer and the metal Fe layer during the same period.The main research contents of this article are as follows:1.The average characteristics of the metal Na and Fe layers over Wuhan were obtained.Based on the 181 night Na lidar data and 199 night Fe lidar data of Wuhan University in the same period,the average characteristics of metal Na layer and Fe layer in the mesopause area over Wuhan(30 N)during this period was obtained.The average centroid height of Na layer is 91.36 km,and the average RMS width(root mean square width)is 4.64 km.The average centroid height of Fe layer is 88.99 km,and the average RMS width is 4.57 km.2.The average night-time and seasonal variations characteristics of the metal Na and Fe layers over Wuhan from 2004 to 2012 are obtained.The metal layer is balanced by the source and sink mechanism,and it is also in a dynamic change.Through data processing,the average nighttime and seasonal variations of the metal Na and Fe layers are obtained.The nighttime change of the Na layer is relatively stable,the peak density of the Na atom number increases in late midnight,the overall RMS width decreases in first midnight,and increases in late midnight.The centroid height of the Na layer increases by 0.36 km all night,and the RMS width increases by0.57 km all night showing symmetry about 00: 00 LT.The seasonal variations of the Na layer shows a half-year periodic oscillation,the maximum and minimum values of the center of mass of the Na layer differ by 1.21 km,and the maximum and minimum values of the RMS width differ by 1.03 km.The night change and seasonal changes of Fe layer are similar to Na layer.3.The inter-annual changes of Na and Fe layers during the same period are extracted.Because of the fact that the metal layer has a small-amplitude nighttime and a large seasonal difference,and the collection time of data samples is symmetricaland more evenly distributed at night,but not seasonally evenly distributed,there are more data in autumn and winter,so when extracting the inter-annual change of the metal layer,the influence of the night change of the data sample can be ignored,but the influence of the seasonal change cannot be ignored.The observation is more frequent in autumn and winter,after making a linear fitting of the data on autumn and winter,we found that the Na layer and the Fe layer were relatively stable during this period.The centroid height of the Na layer decreased only by 58 m in 8 years,the annual change rate was-7.91 m / year,and the RMS width of the Na layer decreased by ? 151 m,The annual change rate is-20.60 m / year.The height of the center of mass of the Fe layer has decreased by 230 m in 8 years,the annual rate of change is-31.36 m / year,and the RMS width of the Fe layer has increased,with an annual rate of change of 21.01 m / year.4.Analyze and discuss various factors that affect the inter-annual change of the metal layer.The long-term changes of the background atmospheric temperature and atmospheric composition in the mesopause area are important factors that dominate the inter-annual change of the metal layer.Drawing on the study of Clemesha and the results of our data processing to obtain the inter-annual variation of the centroid height of the Na layer,it is estimated that the background atmospheric temperature change rate of Wuhan metal layer over Wuhan is about-0.85 K / decade,meaning about 0.85 k per decade.Then we compare the similarities and differences of the inter-annual changes between the Na layer and the Fe layer during the same period.During this period,the two metallic layers are generally stable and there is no obvious change.The centroid height of both of them decreases slightly during this period.The annual rate of change is 4 times that of Na.The absolute values of annual rate of the two layer's RMS width are similar,but the Na layer becomes narrower and the Fe layer becomes wider.