IMP-8 MAGNETOSHEATH FIELD COMPARISONS WITH MODELS

This study presents cross-sectional vector maps of the magnetic field derived from IMP 8 magnetometer in the magnetosheath at 30 R-c 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 t he Spreiter-Stahara gas dynamic (GD) and Fedder-Lyon magnetohydrodynam ic models (MHD). The main purpose is to display the cross-sectional di fferences in relation to the dayside merging with different IMF direct ions, allowing the reader to make direct visual comparisons of the vec tor patterns. It is seen that for east-west IMF direction, the data-ba sed and MHD-based patterns differ noticeably in a similar way from the GD model, presumably reflecting the influence of dayside magnetic mer ging of the Earth's magnetic field with the y-component of the interpl anetary magnetic field. All three northward IMF cross sections show co mparable field draping patterns as expected for a closed magnetosphere . For southward IMF case, on the other hand, differences between the t hree 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 c omparisons 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.