Abstract
This study presents cross-sectional vector maps of the magnetic field derived from IMP 8 magnetometer in the magnetosheath at 30 Re behind the Earth. In addition the vector patterns of the magnetosheath field for northward, southward, and east-west interplanetary magnetic field (IMF) directions are qualitatively compared with those obtained from the Spreiter-Stahara gas dynamic (GD) and Fedder-Lyon magnetohydrodynamic models (MHD). The main purpose is to display the cross-sectional differences in relation to the dayside merging with different IMF directions, allowing the reader to make direct visual comparisons of the vector patterns. It is seen that for east-west IMF directions, the data-based and MHD-based patterns differ noticeably in a similar way from the GD model, presumably reflecting the influence of dayside magnetic merging of the Earth's magnetic field with the y-component of the interplanetary magnetic field. All three northward IMF cross sections show comparable field draping patterns as expected for a closed magnetosphere. For southward IMF case, on the other hand, differences between the three cross-sectional patterns are greater as seen in the field vector sizes and directions, especially closer to the magnetopause where more disturbed magnetospheric conditions are known to be exist. The data comparisons with the MHD and GD models show that the differences result from the magnetic field-flow coupling and that the effects of dayside reconnection are present in IMP 8 magnetic field measurements.Keywords. Vector maps · IMP 8 magnetometer · Inter-planetary magnetic fields
Highlights
The magnetosheath, a thermalized and deected solar wind plasma region between the bow shock and magnetopause, is one of the least studied regions of space
The bifurcation line here is parallel to the IMF direction, northward in this panel, as one expects in the absence of magnetic merging on the dayside magnetopause for northward IMFs
The similarities between the MHD model and both IMP 8 data and the gas dynamics (GD) model vectors seen in this panel are striking
Summary
The magnetosheath, a thermalized and deected solar wind plasma region between the bow shock and magnetopause, is one of the least studied regions of space. The comparisons of the gas dynamic model results with the observational data have shown that in the absence of the magnetic ®eld, the model predicts theow and ®eld behavior in the magnetosheath fairly well (e.g., Zhang et al 1996). My purpose is to compare the cross-sectional vector patterns of the magnetosheath ®eld from IMP 8 data, a gas dynamic model and MHD models. The magnetosheath is studied behind the terminator at A30 Re where magnetic forces have had longer to act on the plasma. This is the ®rst time an MHD model (Fedder et al, 1995; Fedder and Lyon, 1995) is tested against the observational data in the nightside magnetosheath. Brief descriptions of the IMP 8 data and models used for the comparisons follow
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