Vela 3 magnetograms at 18<i>R_E</i>structure and pulsations in the magnetosheath

Abstract

Magnetograms obtained by the third launch Vela satellites in approximately circular orbits at average distances of 18 RE are described, and examples of data from Vela 3A are presented. Special properties of the observed magnetosheath field are: (1) repeated apparent crossings and recrossings of the magnetosheath outer boundary, with individual crossings differing sharply in character from one another; (2) sudden enhancement of measured fluctuation amplitude in sections of the magnetosheath, including apparent ‘double boundary’ structure; and (3) appearance, in 20–50% of the magnetosheath data, of periodic and quasi-sinusoidal oscillations, including elliptically polarized waves, similar in period and appearance to Pc 2, 3, and 4 surface micropulsations in the 6–60-second period range. Pulsation periods are concentrated around 12, 20, 30, and 60 seconds, and recorded sections of periodic character persist from several cycles at the longer periods to several hours at 6–13-second periods. Peak-to-peak amplitude of waves on the measurement plane range from 2 to 50 γ.