Structures and Interannual Variations of the Nocturnal Mesospheric Na and Fe Layers at 30°Normalsize

By analyzing the observational data of the Wuhan University Na and Fe lidars from January 2004 to December 2011, the average characteristics, nighttime and seasonal variations of the mesospheric Na and Fe layers at 30°N are obtained. The average centroid height of the Na layer is 91.36km, while the average RMS (root-mean-square) width is 4.64km. The corresponding results for the Fe layer are respectively 88.99 and 4.57km. Considering the influence of the nighttime and seasonal changes of the Na and Fe layers, we extract the interannual changes of the Na and Fe layers. It is found that both the Na and Fe layers are relatively stable during this period. The centroid height of the Na layer decreases by about 58m in the nearly eight years with an annual change rate of -7.91m, and the RMS width of Na layer decreases by about 151m with an change rate of -20.60m·a^-1. Meanwhile the centroid height of the Fe layer has a decrease of about 230m with an annual change rate of -31.36m·a^-1, and the RMS width of the Fe layer show an increases with an annual change rate of 21.01m·a^-1. In addition, the factors that affect the interannual variation of the metal layer were analyzed, and the similarities and differences between the Na layer and the Fe layer were drawn. Based on our research, it is estimated that the atmospheric temperature in the MLT region over Wuhan has a cooling trend closed to pre decade 0.85K.