Statistical Study On Characteristic Parameters Of Magnetopause Flanks

The solar wind-magnetosphere-ionosphere coupling is an important physical process affecting the Earth's environment,which has attracted extensive attention.Magnetopause is the interface of solar wind and Earth's magnetosphere.At this interface,the solar wind and the Earth's magnetosphere interact violently,and through a series of complex physical processes,the plasma and energy from the solar wind are input into the Earth's magnetosphere.Therefore,the magnetopause is a very important region for the solar wind-magnetosphere-ionosphere coupling.The magnetopause characteristic parameters can be used to describe the structure and dynamics of the magnetopause and help us to understand the various physical processes occurring at the magnetopause.However,most of the previous studies were focused on the dayside,and there are only few relevant studies on the magnetopause flanking region.This paper discusses the characteristics of the magnetopause.Based on satellite observations of Cluster(C3),this paper analyzes the crossing events of the low-latitude(less than 450 in the GSE coordinate system)dawn(magnetic local time 02<MLT<08)and dusk(22>MLT>16)flanks of the magnetopause between 2001 and 2009.The main work is as follows:(1)The characteristic parameters such as the thickness,velocity and average current density of the lateral magnetopause are calculated by using the Faraday residual minimizing analysis(MFR analysis)and Dehoffmann-Teller analysis(HT analysis)respectively;(2)The rotational discontinuities and tangential discontinuities of the magnetopause are divided by using the Walen test,and the statistical results are given;(3)The upstream ? values near the magnetopause(the ratio of plasma thermocompression to magnetopause)are collected and used to analyze the relationship between the upstream ? and the characteristic parameters of the magnetopause,and to analyze the influence of the upstream ? on the Walen relations of the parameters on both sides of the magnetopause;(4)Considering the parker spiral structure of the solar wind may result in the differences in the upstream shock wave normal direction on both sides of the magnetopause flanks.In this paper,the data of interplanetary magnetic field at the nose tip of bow shock provided by OMNI database are used.The angle between the direction of the interplanetary magnetic field and the normal direction of the magnetopause on both sides of the flanks was calculated.The influence of the angle on the parameters of the magnetopause is briefly analyzed.The results show that:(1)The thickness and motion of the magnetopause on both sides of the dawn and dusk show an upward trend from the near dayside to the near tail side.At the same time,the characteristic parameters of the magnetopause on both sides of the dawn and dusk show obvious asymmetry,that is,the thickness of the dawn magnetopause is thicker and the motion is more active.The degree of asymmetry increases first and then decreases from the near dayside to the near tail side in space;(2)The cases of rotational discontinuity on both sides of the dawn and dusk accounted for a certain proportion,reaching about 20%,and the dawn side is slightly higher than the dusk side;(3)The upstream ? values show a downward trend from the near dayside to the near tail side on both sides,but show an abnormal increase in part of the dusk side.The upstream ? values of the magnetopause show an obvious asymmetry,which is not obvious in the near dayside of the magnetopause,and then increases suddenly in a certain region.In addition,by analyzing the effect of ? on the magnetopause thickness and motion,it is found that higher upstream ? corresponds to thinner and more active magnetopause,but the asymmetry of upstream ? is not the main cause of the asymmetry of the magnetopause thickness and motion;(4)The angles between the normal magnetopause and the interplanetary magnetic field on both sides of the dawn and dusk show no significant difference in statistical results.At the same time,there is no obvious evidence that different upstream shock normal can cause significant changes in the macroscale parameters of the magnetopause.In conclusion,the characteristic parameters of the magnetopause show a dawn-dusk asymmetry,which may not be caused by a single upstream parameter,but is the result of the combined contribution of multiple factors on both sides of the magnetopause.In addition,since the discontinuous rotation of the magnetopause flank also accounts for a considerable proportion,the study of the energy transfer in the flank region and the related physical processes should also be paid attention to.Finally,in view of the important significance of the eigenvalue of ?,the abrupt uplift of the upstream ? value in a certain region observed in part of the dusk side is worth further analyzing and discussing.