Propagation of inclined interplanetary shock through the magnetosheath

Abstract

Normals of most interplanetary shocks are nearly aligned with the Sun–Earth line. But some shocks, especially those connected with corotating interaction regions, are sufficiently diverted from the typical orientation near 1 AU. We obtain that shocks with normal lying in the XY plane and inclined at an angle about 40° or more from the Sun–Earth line can result in sudden impulse variations of different magnitudes in the dawn and dusk magnetosphere. Using the Rankine–Hugoniot equations, we calculate the downstream velocity in dependence on the interplanetary shock orientation. We find for given upstream parameters that the downstream velocity V y ≃ 0.2 V x , when n y ≃ n x and the upstream velocity is directed exactly along the Sun–Earth line. For more inclined shocks, the ratio V y / V x may exceed 30 percent. Numerical three-dimensional (3-D) MHD simulations predict a set of MHD discontinuities propagating through the magnetosheath after interaction between an inclined shock and the bow shock. It is shown a clear difference between variations in the dusk magnetosheath downstream of the quasi-perpendicular bow shock (the region passed first by the inclined interplanetary shock) and in the dawn magnetosheath downstream of the quasi-parallel bow shock. In the dusk flank, the predicted variations are mainly similar to those obtained previously for a radially propagating shock at the Sun–Earth line. In the dawn flank, the forward fast shock with a small variation of the magnetic field magnitude is followed by another compound discontinuity bringing an increase of the density and magnetic field, but a decrease of the velocity and temperature. We suppose that this discontinuity consists of several basic MHD discontinuities moving with close velocities, therefore its composition cannot be determined exactly in 3-D simulations. Using an estimation of the Alfvén velocity in the magnetosphere, we find the transit time of the fast shock from the first impact at the bow shock to the ionosphere. This transit time is obtained to be 0.5–1 min longer for the inclined shock than for a radially propagating shock with a similar amplitude.