Heavy ion circulation in the Earth's magnetosphere

Abstract

We propose a mechanism whereby singly charged heavy ions from the plasmasphere are convected intermittently to the dayside magnetopause, accelerated there, swept into the distant tail lobes and boundary layer and convected earthward in the plasma sheet to re‐enter the inner magnetosphere. The outer region of the plasmasphere is known to be stripped off during periods of enhancement of the convection electric field. These cold plasmaspheric ions drift toward the dayside magnetopause where they may become accelerated and co‐mingled with magnetosheath plasma either through magnetic merging or some viscous process operating at the magnetopause. If the ion motion at the magnetopause is poleward, the ions may become part of the entry layer, entering the cusp and exiting as part of the plasma mantle. The cross‐tail electric field will cause them to drift into the lobes toward the center of the tail, ultimately reaching the plasma sheet in the distant tail. If the ion motion at the dayside magnetopause is equatorial, the plasmaspheric ions become part of the boundary layer, again ultimately reaching the plasma sheet in the distant tail. Once in the plasma sheet some of the heavy ions may flow back toward the earth and re‐enter the magnetosphere as energetic ions.

The fate of the outer plasmasphere

“…There is plenty of evidence that outer plasmasphere material can convect to the magnetopause. During geomagnetic storms, cold plasmaspheric ions are commonly seen immediately adjacent to the magnetosheath and/or low-latitude boundary layer (LLBL) in the noon and mid-afternoon local time sector [Freeman, 1969;Borovsky et al, 1996;Elphic et al, 1996, and references therein]. Even at non-storm times, cold ions are caught up in the LLBL convection [Gosling et al, 1990], and are accelerated during transmission through or reflection from the magnetopause [Fuselier et al, 1991 ].…”

Plasma plume circulation and impact in an MHD substorm

“…[2] Observations have increasingly revealed that enhanced magnetospheric circulation, driven by the solar wind and its linked interplanetary magnetic field, results in the transport of the outer layers of the plasmasphere toward the dayside subsolar magnetopause, creating ''plasmaspheric plumes'' [Grebowsky, 1970;Chappell et al, 1970Chappell et al, , 1971Freeman et al, 1977;Sandel et al, 2001;Goldstein et al, 2004;Chandler and Moore, 2003;Moore, 2004, 2006]. The plasmasphere is supplied by a light ion outflow analogous to the polar wind, commonly known as ''refilling flows'' because they flow on closed low-latitude flux tubes and build up substantial densities over several days.…”

Global estimates of plasmaspheric losses during moderate disturbance intervals

“…After reaching the dayside magnetopause, plasmaspheric material can then be transported on reconnected field lines over the polar cap and down the magnetotail (Su et al, , 2001a. It is unclear what portion of the formerly plasmaspheric material is drained down the magnetotail and lost to the solar wind as opposed to entering the plasma sheet and being eventually recirculated into the inner magnetosphere (Freeman et al, 1977;Elphic et al, 1997;Borovsky et al, 1997). Plasma sheet ion density and composition measurements (e.g., Lennartsson and Shelley, 1986) suggest that although some fraction of this eroded plasmaspheric material may join the plasma sheet, the vast majority of it is likely lost to the solar wind before the field line reconnects in the distant magnetotail.…”