Interaction Between IMF Discontinuities or Shocks and the Earth’s Bow Shock

The study of the propagation and evolution of interplanetary disturbances, shocks and discontinuities through the magnetosheath is critical to improve our understanding of the Sun-Earth system. It’s necessary to study interaction of the Earth’s Bow Shock (BS) with interplanetary discontinuities, because the interactions influence the Earth’s magnetosphere. In this paper we discuss various types of interactions between these events and the Earth’s bow shock. Introduction Early spacecraft measurements of the interplanetary magnetic field revealed the presence of large changes in direction, sometimes accompanied by magnitude changes, over tens of seconds [Horbury et al., 2001]. These events are usually considered to be either rotational (RD) or tangential (TD) MHD discontinuities. Other MHD events MHD shock waves are often observed in the solar wind. An interaction between these events and the Earth’s bow shock is the main topic of this paper. The propagation of these events in solar wind could can be described by front angle, which is the angle between the direction of the solar wind velocity and the magnetic field [Richardson and Paularena, 1998]. To study solar wind structures [Lin, 1997], it can be used a lot of methods of analysis: one, two or three-dimensional [Cable and Lin, 1998; Zhuang et al., 1981; De Sterck and Poedts, 1999] MHD simulations, hybrid simulations or time series data analysis [Song and Russell, 1999], multiple spacecraft observations [Russell et al., 1983], [Horbury et al., 2001]. Most time series analysis can be divided into three categories: discontinuity analyses, wave analysis and correlation analysis. Magnetic field discontinuities are often classified using the Smith [1973] method (Table 1), on basis of magnetic field at an event that involves the normal component, B · n/|B|, n is the estimated normal vector, and the relative change in magnitude △|B|/|B|, where △|B| is the difference in |B|. NDs are inconsistent with MHD RDs or TDs, while EDs could be both types. Discontinuities can be also classified according to jumps of plasma parameters and magnetic field across the discontinuity. Solar wind velocity in normal direction does not change ([vn] = 0) over the MHD discontinuities. Brackets denote a jump in normal velocity across the front. Shocks are structures, where the solar wind velocity in normal direction changes over the front ([vn] 6= 0). 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 ◦, oblique and parallel θBn = 0 ◦. Later this classification was completed by quasi-perpendicular θBn > 45 ◦ and quasi-parallel θBn < 45 ◦ shocks. According to jumps of plasma parameters, shocks were classified as fast/slow shocks and forward/reverse shocks (Table 2).Fast and slow shocks have been described by Burlaga [1971]. Table 1. Four classes of discontinuity events. Type of discontinuity B · n/|B| △|B|/|B| Rotational(RD) ≥ 0.4 < 0.2 Tangential (TD) < 0.4 ≥ 0.2 Either (ED) < 0.4 < 0.2 Neither (ND) ≥ 0.4 ≥ 0.2 Table 2. Changes of plasma parameters across shocks in the solar wind. Np means concentration, Vth thermal velocity, vsw solar wind velocity, and B magnetic field. Shock vsw Np Vth B forward fast shock FFS increase increase increase increase reverse fast shock RFS increase decrease decrease decrease forward slow shock FSS increase increase increase decrease reverse slow shock RSS increase decrease decrease increase WDS'05 Proceedings of Contributed Papers, Part II, 213–219, 2005. ISBN 80-86732-59-2 © MATFYZPRESS