Propagation of Interplanetary Shocks into the Earth’s Magnetosphere

A thorough study of the propagation of interplanetary shocks of various origin through the Earth’s magnetosphere is expected to improve our understanding of the Sun-Earth system. The interplanetary shocks interact with the bow shock and cause pressure pulses on the magnetopause and its movement, launching different waves into the magnetosphere. Therefore geosynchronous satellites (GOES, LANL) and satellites in the outer magnetosphere, as well as ground-based stations register arrivals of the interplanetary shocks. In this study, we try to find their propagation velocity in the Earth’s magnetosphere and probable influence of the foreshock on the interplanetary shock fronts in the magnetosphere. According to our study, the shock speeds are in the Earth’s magnetosphere higher than in the solar wind. The analysis utilizes data from simultaneous observations of interplanetary shocks from available satellites in the solar wind and the Earth’s magnetosphere such as ACE, Wind, IMP–8, Interball–1, Geotail, Polar, and GOES series. Introduction The study of the propagation of interplanetary shocks through the Earth’s magnetosphere is fundamental to improve our understanding of the Sun-Earth system. Interplanetary shocks (IPSs) are structures, which can propagate in the solar wind and across planetary magnetospheres. The solar wind velocity component in the shock normal direction changes over the shock front ([vn] 6= 0). Magnetohydrodynamic shocks were divided according to angle θBn , the angle between the direction of the shock front normal and the upstream magnetic field, as perpendicular θBn = 90 ◦ and parallel θBn = 0 . As strictly parallel or perpendicular shock are not usually found, this division was completed by quasiperpendicular θBn > 45 ◦ and quasi-parallel θBn < 45 ◦ shocks. According to jumps of plasma parameters and magnetic field strength, shocks were classified as fast/slow shocks and forward/reverse shocks. Fast and slow shocks have been described by Burlaga [1971]. Interplanetary shocks are driven by two main sources 1) coronal mass ejections/magnetic clouds (CME/MC) and other solar transients and 2) corotating interaction regions (CIR). Because of the very large scale of both phenomena, interplanetary shocks are generally expected to be plane (Russell et al. [2000]) — at least for the Earth’s magnetosphere cross-scale size. Several authors (e.g, Szabo et al. [2001]) show that some observations would be better explained by a curved surface of IPS. The occurrence rate and mean strength of the interplanetary fast shocks appear to correlate with the solar cycle (Berdichevsky et al. [2000]). The interaction of fast forward shocks with the Earth’s magnetosphere has been studied by Villante et al. [2004]. Considering propagation of planar shock fronts along normal direction, they found time delay about 5 minutes from the bow shock to the ground for almost radially propagating structures. They also estimated magnetosheath speed of shock about of ∼ 1 3 − ∼ 1 4 of the external shock speed. The passage of interplanetary discontinuities through the subsolar magnetosheath has been examined by Farrugia et al. [1989]. They presented sudden changes of the Earth’s magnetopause location on September 9-10th, 1978. These magnetopause motions were accompanied by disturbances of the geomagnetic field on the ground. The authors performed a detailed study of the magnetopause motions and corresponding ground magnetic signatures. Other authors, e.g. Lepidi et al. [1996], studied also bow shock motions during variable solar wind conditions. WDS'06 Proceedings of Contributed Papers, Part II, 7–13, 2006. ISBN 80-86732-85-1 © MATFYZPRESS