The Investigation Of The Three-Dimensional Asymmetric Magnetopause Model

Based on the problems and the limitations among previous low-latitude and high-latitude magnetopause empirical models, the statistical studies and the modeling about the magnetopause size and shape are carried out continuously in this thesis.Based on the magnetopause crossings from many satellites and the Levenberg-Marquardt method for nonlinear multi-parameter fitting, a new dynamic three-dimensional asymmetric magnetopause model is developed finally. This model is important for the theoretical research about the interaction between solar wind and the Earth magnetic field. It is also useful for the space weather applications.In this thesis, we collect 1226 magnetopause crossings from Geotail, IMP8, Interball, TC1, THEMIS, Wind, Cluster, Polar, LANL and GOES with the corresponding 5-minute average solar wind parameters from ACE or Wind. The solar wind propagating time from ACE or Wind to the magnetopause crossings is mainly determined by matching the clock angle of the interplanetary magnetic field (IMF) or the interplanetary plasma parameter variable profile with that of the magnetosheath. When analyzing and fitting the high-latitude magnetopause, the 1248 Hawkeye magnetopause crossings from the website with the hourly solar wind parameters are also used.In order to improve the low-latitude magnetopause empirical model, a continuous function between the IMF BZ and the magnetopause size and shape is introduced. Based on this function, the Shue model function, the 631 low-latitude magnetopause crossings (including their corresponding upstream solar wind data), and the Levenberg-Marquardt method for nonlinear multi-parameter fitting, a new low-latitude magnetopause model has been constructed and parameterized by the solar wind dynamic pressure (DP) and IMF BZ. In comparison with previous low-latitude magnetopause models on the basis of our database, it is found that the new low-latitude model improves the prediction capability and has a larger range of validity. In addition, it is also demonstrated that the new model and previous low-latitude magnetopause models are not appropriate for predicting the high-latitude magnetopause.In order to get the high-latitude magnetopause characteristics, we analyze these 2708 magnetopause crossings in the near-Earth space, and conclude that: (1) the magnetopause is indented in the cup region with a large indented scope; (2) the location of the magnetopause indentation is controlled by the dipole tilt angle, which almost linearly influences the zenith angle of the magnetopause indentation vertex and whose influences on the north and the south magnetopause indentations are almost anti-symmetric; (3) the depth and the scope of the magnetopause indentation and the invariant latitude corresponding to the center of magnetopause indentation are almost not influenced by the dipole tilt angle.In order to develop a three-dimensional magnetopause model, a new model function is proposed, which can describe the global magnetopause, including the asymmetries and the indentations. This model function also has other merits, for example, an extrapolated ability for the distant tail magnetopause and the physical significance.Based on this new model function,the above 2708 magnetopause crossings and the Levenberg-Marquardt method for nonlinear multi-parameter fitting, the important parameters for the magnetopause have been screened out, and a new dynamic three-dimensional asymmetric magnetopause model has been developed step by step over the divided regions and parameterized by the solar wind dynamic and magnetic pressures (DP+BP), IMF BZ, and the dipole tilt angle. In comparison with previous empirical magnetopause models based on our database, the new model improves prediction capability of describing the three-dimensional structure of the magnetopause. It is shown that this new model can be used to quantitatively study how the dipole tilt angle influences the north-south asymmetry and the indentations,how DP+BP compresses the magnetopause, how IMF BZ erodes the magnetopause. In addition, this model is not only appropriate to predict the near-Earth magnetopause for various solar wind conditions but also can provide a reasonable estimation of the distant tail magnetopause under normal solar wind conditions.