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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L23106, doi:10.1029/2006GL027110, 2006

Timescale for the formation of the cold-dense plasma sheet: A case study

Simon Wing

Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA


Jay R. Johnson

Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA


Masaki Fujimoto

Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan


Abstract

The timescale for the formation of cold-dense plasma sheet ions was investigated with an event in which the interplanetary magnetic field (IMF) was northward for almost one day. The plasma sheet dawn and dusk flanks appear to reach cold dense states (n > 1 cm−3; T < 2 keV) within a few hours after IMF northward turning. Closer to the center (midnight meridian), the ion temperatures reach < 2 keV within a few hours of IMF northward turning, but the ion densities do not reach above 1 cm−3 for at least ∼8 hours after IMF northward turning. The connection between solar wind ions and plasma sheet cold-component ions is demonstrated. The plasma sheet dawn flank ions appear to lag the solar wind ions by about 3 hours. This study confirms the previous statistical results: (a) the densification of the plasma sheet can be attributed to the influx of the cold-component (magnetosheath/solar wind origin) ions; and (b) the cooling of the plasma sheet can be attributed not only to the influx of the solar wind ions, but also to the cooling of the hot components. Order of magnitude calculations of the plasma sheet filling rate from reconnection and diffusion suggest that both entry mechanisms could result in roughly comparable filling rates. Hence, the dawn-dusk asymmetries would be key in distinguishing the roles of the various proposed entry mechanisms.

Received 5 June 2006; accepted 2 November 2006; published 9 December 2006.

Keywords: plasma sheet; transport; cold-dense.

Index Terms: 2764 Magnetospheric Physics: Plasma sheet; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2748 Magnetospheric Physics: Magnetotail boundary layers; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2744 Magnetospheric Physics: Magnetotail.

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Citation: Wing, S., J. R. Johnson, and M. Fujimoto (2006), Timescale for the formation of the cold-dense plasma sheet: A case study, Geophys. Res. Lett., 33, L23106, doi:10.1029/2006GL027110.