Vela 2 measurements of the magnetopause and bow shock positions

Abstract

Extensive measurements of the positions of the earth's magnetopause and bow shock have been performed with the Vela 2 satellites at ∼17 RE (earth radii) and at ecliptic latitudes up to ±63°. It has been found that these positions are highly variable in time; there is evidence that some of this variability is due to the changing character of the solar wind. In particular, the average positions of the magnetopause and shock appear to be related to the magnetic disturbance index Kp and thus also to solar wind velocity. Specific examples of data have been found that can be interpreted as showing gross motions of either the magnetopause or shock at times of sudden changes in plasma pressure within the magnetosheath. Despite the large variations in the magnetopause and shock positions, it has been found that solar magnetospheric and solar ecliptic coordinates are both useful coordinate systems for ordering the boundary positions. However, solar magnetospheric coordinates appear to be slightly preferable at high latitudes. In either system, both the magnetopause and the shock exhibit an east-west tilt of about 2–4° relative to the sun-earth line.