Spatial variations of the magnetosheath magnetic field

Abstract

Measurements by Explorers 28, 33, 34 and 35 have been used to study the spatial characteristics of the magnetic field in the magnetosheath to a distance of 70 R E behind the Earth. During 1966–1967 there were 1661 hr when one spacecraft of this multi-satellite system was monitoring the interplanetary medium while at least one other satellite was making magnetosheath measurements. This has made possible a separation of time and space variations and has permitted a study of the direction and magnitude of the magnetosheath field as a function of position and interplanetary field orientation. Results indicate that the mag-netosheath field is several times the strength of the simultaneously measured interplanetary field in the sunward magnetosheath. This magnetosheath to interplanetary magnitude ratio decreases with distance from the subsolar point to values which are frequently less than unity at distances beyond 30 R E and away from the bow shock. This ratio also displays a dawn-dusk asymmetry which is dependent on the interplanetary field orientation. Interplanetary field lines perpendicular to the Earth-Sun line are associated with symetrically distorted magnetosheath field lines in the dawn and dusk hemispheres and are consistent with the draping of field lines around the magnetosheath. When the interplanetary field is aligned near the spiral angle, fields measured in the dusk hemisphere are much more ordered than those measured in the dawn hemisphere behind the Earth. These experimental results are in general agreement with the theoretical predictions of the gasdynamic model.