The superdense plasma sheet: Plasmaspheric origin, solar wind origin, or ionospheric origin?

Abstract

A few times per month, the density of the plasma sheet is several times higher than its usual density. Such superdense plasma sheet intervals are observed both in the midtail region and at geosynchronous orbit. Typically at geosynchronous orbit, a superdense plasma sheet occurs on the first day of a geomagnetic storm and lasts about 12-18 hours. The occurrences of superdense plasma sheets are found to be related to a distinct pattern of Kp: Kp rising after it has been low for an extended period. The occurrences are also associated with high-density solar wind. Three sources for the material of the superdense plasma sheet are explored: (1) the outer plasmasphere, which is stripped away and drawn into the dayside neutral line when Kp increases, wherein it joins the lobe and eventually joins the plasma sheet; (2) high-density solar-wind, which may have its entry into the plasma sheet controlled by the solar-wind magnetic field; and (3) ionospheric outflow, which is known to be Kp dependent. The occurrence of a superdense plasma sheet has several consequences: it adds to the intensity of the ring current, it may alter the dynamics of the magnetotail and the nature of substorms, and it may provide an enhanced source population for storm-time energetic particles. Copyright 1997 by the American Geophysical Union.