PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
Figure 1: Temporal profiles at fixed points in the XY (equatorial) plane. On the left side, the points are in the
dusk magnetosheath: (x,y)=(6.0,12.0) shown by red color and (6.7,13.3) shown by blue color. On the right
side, the two points are symmetrical with respect to the XZ (meridional) plane. An imaginary observer on both
flanks registers an interplanetary shock (IS) and a compound discontinuity (CD). However a reflected fast shock
(RFS) or a solar wind passage (SW) are predicted only in the dusk magnetosheath.
of the MHD parameters in the XY plane (not shown) confirm that the normal of the reflected shock is nearly
aligned with the normal of the coming IS.
4 Observations in the magnetosheath
Propagation of an oblique IS through the magnetosheath was studied by Pˇrech et al. (2008) using recent
Themis data. The oblique shock was identified in the supersonic solar wind by ACE, Wind, SOHO, and Cluster
(near the bow shock). The orientation of the shock normal is similar to that used in the present simulation
(i.e. Nx ≈ Ny < 0). Themis A, B, C, and D were in the dusk dayside magnetosheath, whereas Themis
E was in the magnetosphere prior the IS arrival. All Themis, including Themis E, observed the IS related
discontinuity. Several minutes later the IS arrival, Themis B, C, and D observed the bow shock crossing, while
Themis E crossed the magnetopause after ≈ 20 sec. The compound discontinuity with anti-phase variations
of the density and temperature was registered by all Themis where the plasma measurements were available.
Figure 2 shows the magnetic field magnitude, the density, the temperature, and the Vx velocity observed by
Themis C during 10 minutes interval.
Themis C registered the IS at 0822:36 UT, having the GSE coordinates (6.5, 11.3, -3.1) RE. The CD was
observed there 70 sec later. The clear signatures of this discontinuity are increase of the density and decrease
of the temperature. The fluctuated magnetic field also increases, while the velocity varies insufficiently. Using
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