Magnetic field draping against the dayside magnetopause

Interplanetary magnetic fields observed upstream of Earth's magnetosphere at ISEE 3 form input for a gas dynamic model of magnetic field draping in the dayside magnetosheath. Model results near the magnetopause are compared with appropriately lagged observations at ISEE 1. In 16 of 24 cases the angle between the transverse component of the model and observed fields is less than 20°. The agreement is surprisingly good in view of the uncertainty introduced by the large distances between ISEE 1 and ISEE 3. The results indicate that magnetohydrodynamic and energy transfer processes at the magnetopause do not cause large distortions of the magnetosheath magnetic field. In addition, a comparison between observed and model field magnitudes indicates that immediately outside the magnetopause the observed field behaves like the model field at a distance of ∼0.5 R E from the magnetopause, outside the region where magnetohydrodynamic effects make the gas dynamic model inapplicable. Patterns of model magnetic field orientation at the magnetopause are presented for practical application.