Survey On The Magnetic Structure Of The Magnetotail Neutral Sheets And Cusp

The geometrical configuration of magnetic field lines (MFLs) plays crucial roles on the magnetospheric dynamics. In order to study the magnetic structure, the researchers put forward some methods, and satellite projects have been launched to provide data support for these methods in recent years. Neutral sheets (NS) and cusp are active areas in magnetosphere and a study of their the magnetic field structure is conducvice to undestand the evolution of magnetosphere. Based on the multipoint magnetic observations of Cluster and the associated analysis methods (MCA, MRA), the magnetic field structure in magnetotail NS and cusp are statistically surveyed. The main results of the study are(1) An empirical model (GSM) applied to YZ plane of the three-dimensional structure of the magnetic field lines in the NS has been developed, representing it as a function of the positional parameter Y:a cubic function is selected to reveal the relationship between Y and Z; the relation between Y and the magnetic field values a quadratic function and indicates that magnetic field values is weak at midnight region and increases gradually to the duskside and dawnside; the relation between Y and curvature radius is published by a quadratic function, and the curvature radius Rc of flattened CS is less than the normal CS; the relation between the azimuthal angle of the curvature vector and Y is negatively correlated; the polar angle of the normal of the osculating plane is uncertain in the center area, but is close to 90° at the dawnside and duskside. The current density which is also statistically surveyed in this work.(2) During the period from July 2001 to October,44 southern cusp crossing events are selected from Cluster to investigate the magnetic field structure. It is showed that some parameters have obvious fluctuation in internal cusp region than the two sides of the cusp; the configuration of southern cusp is flattened and tilts toward the dayside at the dawnside, every element of magnetic field are different between the dayside and the nightside; in internal cusp region, Bx has larger value within the azimuth scope 70°～150°, By,Bt and φB increase with the increase of azimuth angle, but Bz decreases with the decrease of azimuth angle, and θB is constant (～143.4°), each element of ▽B, Rc and j is very complex; during a magnetic storm, every component of magnetic field and X are both significantly increased, but both X and width of the cusp are reduced, the mean and standard deviation of some parameters (j,ne and ▽B) increase and that of Rc decrease in internal cusp region, every component of magnetic field recovers rapidly but some parameters (j, ne and Te) would delay recovery in plasma mantle region.