Statistical Study On Plasmapause Position Of The Earth

The Earth’s plasmasphere is an important area connecting the ionosphere and magnetosphere. The structure of the plasmasphere is affected by the interactions of the ring current, the radiation belt and the upper ionosphere in the inner magnetosphere. Therefore, research on the structural changes of the plasmasphere has important scientific significance.The plasmaspheric He+ resonantly scatter the sunlight at 30.4 nm with relatively strong intensity. The global images of the plasmasphere were obtained for the first time by IMAGE/EUV imager. Many structures of plasmasphere including shoulder, plume and plasmapause were found from EUV images. These structures change with the solar wind and geomagnetic activities. Therefore, this thesis will focus on investigating the relationship between the plasmapause locations and geomagnetic activities or upstream solar wind.Based on the plasmaspheric images observed by IMAGE EUV imager,the plasmapause locations on the magnetic equatorial plane are reconstructed with the Minimum L Algorithm. Totally 3579 plasmaspheric images are selected from 2000 to 2002 and a plasmapause location database containing 48899 plasmapause locations in 1 h MLT intervals is compiled. This database is used to statistically study relationships between the plasmapause locations and geomagnetic activities. It is found that the plasmapause shapes are highly dependent on the geomagnetic activities, and the plasmapause locations are negatively correlated with Kp, Dst and AE with their variation tendencies all significantly changing with MLT. It is also found that the effects of the substorm activity to the plasmapause locations are different under different geomagnetic activities with the effects being larger for quiet periods compared with disturbed periods. The results in this paper will provide an important basis for future construction of a plasmapause model and for understanding the dynamic structure of the plasmapause.The propagation time of the upstream solar wind data obtained by ACE satellite is calculated based on Shepherd’s method to shift the solar wind parameters to the magnetosphere. Then the shifted solar wind parameters are matched with the plasmapause locations. It is found that the plasmapause shapes are strongly correlated with the solar wind speed (Vsw) and the z component of the interplanetary magnetic field (IMF Bz), which are two most important parameters for solar wind-magnetosphere coupling and inner magnetospheric dynamics. The plasmapause locations also change with variations of the solar wind number density (Nsw) with smaller correlation coefficient compared with Vsw and Bz.It is found that the plasmapause locations are negatively correlated with Vsw, indicating that an increase in Vsw results in a decrease of the plasmapause location. As the absolute values of IMF Bz increase, the plasmapause also moves towards the Earth. Fittings of the plasmapause locations to the solar wind parameters in different MLT sectors indicates that the variations of the plasmapause with solar wind parameters are different in MLT, and the influence of MLT must be considered when establishing a plasmapause location model driven by solar wind parameters.Investigations in this thesis provide an important basis for the establishment of a plasmapause model and the study of the dynamic structure of plasmapause in future. The results in this thesis can also potentially be used to forecast the plasmapause locations in future.