ИСТИНА

We present a case event of THEMIS and ground-based observations of the magnetopause and geomagnetic field perturbations related to a discontinuity of interplanetary magnetic field (IMF) passing through the magnetosheath. As observed by the ACE upstream monitor, the IMF discontinuity is rotational, i.e. it is characterized by sudden change of the IMF orientation without any changes in solar wind plasma characteristics. The normal to IMF rotation plane is inclined duskward and northward. During passing through the magnetosheath, the discontinuity forms a pressure pulse. THEMIS detects very strong local compression, where the total magnetosheath pressure is revealed to be 3 times higher than the upstream solar wind dynamic pressure. The magnetosheath compression is contributed by enhanced thermal ion and magnetic pressures. A substantial depletion of the magnetosheath pressure is revealed at the leading and trailing edges of the pressure pulse. This spatial heterogeneity in the magnetosheath causes a local distortion of the Chapman-Ferraro current (CFR) and, hence, transient outward – inward – outward magnetopause motion with amplitude of more tan 1.5 Re. The transient motion results in a significant local deformation of the magnetopause shape that is revealed as a substantial deviation of the magnetopause normal from its nominal direction. Inside the magnetosphere, the CFR distortion is detected by THEMIS as a magnetic variation of very high amplitude of ~40 nT. The INTERMAGNET network of ground-based magnetometers allows tracing the movement of the CFR distortion related to the propagation of discontinuity through the magnetosheath. We find that the variation in horizontal component of geomagnetic field propagates from south to north and from dawn to dusk that is in good agreement with the IMF discontinuity orientation observed by ACE.