A macroscopic profile of the typical quasi‐perpendicular bow shock: Isee 1 and 2

Open Access
Publisher Website
Google Scholar
Abstract
Field and particle properties of the bow shock recorded on November 5, 1977, identified earlier as stable features by comparison of Isee 1 and 2 data, are examined macroscopically. The extent to which the shock was in a ‘typical’ state is described, and multidiagnostic observations are combined to define the shock profile, which, in this known case, is reminiscent of composite portraits assembled from earlier studies. A foot, a principal wave front gradient, and a postfront overshoot characterized the magnetic field. Various particle measurements revealed corresponding structural elements, including a bimodal ion energy distribution whose two peaks were at roughly the solar wind streaming energy and 2 to 3 times the streaming energy. The electrons were thermalized before the principal sharp magnetic gradient; the ions were partially randomized at the gradient, but the ion thermalization process was not completed until long after the gradient was crossed. The second peak of the ion distribution represented a separate group of reflected particles upstream of the main magnetic gradient that retained its identity for an appreciable distance behind the front before being merged by thermalization into the general distribution. This separate group included a northward proton flux in front of, but not immediately behind, the front. The group ultimately became thermalized through a series of very regular oscillations. The decrease in solar wind bulk velocity at the front exceeded the sum of that calculated from an idealized first‐order model of the rise in potential opposing the flow, plus the proton heating, leaving proton reflection and wave radiation and dispersion as candidates to account for the discrepancy. Plasma wave activity, at ion acoustic frequencies, was most intense in the foot and at the front and appeared to be enhanced at the outer boundary of the reflected particles.