The Dynamic Characteristics of Sequential E_s in the Ionosphere

In this paper, the phenomenon E_ss appearing in the daytime ionograms at Wuchang station (114°21.5'E,30°32.7'N) during the period 1964-1973 is analysed. It is discovered that the characteristics of this daytime phenomenon E_ss are very similar to those of the nighttime phenomenon Em called '"nighttime thick-layer of motion". It is found that: (1) the heights of both E_ss-layer and Em-layer descend gradually and their thickness become rather thinner during the processes of their formation and development; (2) their appearance rates are independent upon the geomagnetic actively Kp or the sunspot number R; (3) both of them mainly appear in winter and spring. Of course, their diurnal behaviour are difference the E_ss mainly appear in the afternoon while the Em mainly appear after midnight. Therefore, It is concluded that both E_ss and Em are conneced with the convergent null in the vertical drift velocity of ionization, i.e., these phenomena are caused by the same dynamic process in the vally region of the ionosphere.