Temporal variations in the magnetosheath: Comparison between MHD calculations and observations for one event on September 17, 1978

Plasma density and magnetic field data from ISEE 3 on September 17, 1978 upstream of the Earth's bow shock are used to calculate a 3D MHD flow in the dayside magnetosheath. The numerical results are compared with the ISEE 2 magnetosheath data along a complete dayside crossing from the magnetopause to the bow shock. Such approach gives an opportunity to estimate the ability of the MHD numerical model to predict temporal variations of the MHD parameters in the magnetosheath. We discuss properties of a particular structure in the inner magnetosheath identified previously by Song et al., as a slow mode transition region (Geophys. Res. Lett. 17 (1990) 2035). Our results show that the quantitative characteristics of the density and magnetic field in this structure may be explained by temporal variations of these parameters in the supersonic solar wind if two different time shifts obtained by Hubert (Geophys. Res. Lett. 28 (2001) 1451) are taken into account. This study stresses importance of the interplanetary magnetic field variations in the formation of MHD flow in the magnetosheath.