Statistical analysis of the plasmoid evolution with Geotail observations

Details Statistical analysis of the plasmoid evolution with Geotail observations Statistical analysis of the plasmoid evolution with Geotail observations

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...103.4453i&link_type=abstract

Journal of Geophysical Research, Volume 103, Issue A3, p. 4453-4466

Physics

121

Magnetospheric Physics, Magnetospheric Physics: Magnetotail, Magnetospheric Physics: Plasma Sheet, Magnetospheric Physics: Storms And Substorms

Scientific paper

Plasmoids in the Earth's magnetotail were studied statistically, using low energy particle (LEP) and magnetic field (MGF) data from the Geotail spacecraft. Their evolution along the tail axis from XGSM'=-16 to -210RE was investigated with 824 plasmoid events. Their dependence on YGSM' was studied as well to derive the three-dimensional structure of the plasmoids. (The coordinates are aberrated to remove the average effects of the orbital velocity of the Earth about the Sun.) We defined a plasmoid as a structure with rotating magnetic fields and enhanced total pressure. In the near tail (XGSM'>=-50RE), there was a tendency for the plasmoids to be observed in the premidnight sector around the tail axis (|YGSM'-3|<=10RE), while they were observed widely (|YGSM'|<=20RE) in the middle tail (-50>XGSM'>=-100RE) and in the distant tail (-100RE>XGSM'). The plasmoids expanded in the +/-YGSM' direction with typical velocities of +/-130+/-100km/s in the near tail. This strongly supports the view that plasmoids are initially formed at the near-Earth neutral line which has a limited extent in the YGSM' direction. The plasmoids accelerated in the downtail direction from 400+/-200km/s to 700+/-300km/s from the near to the middle tail. Then, it is suggested that they decelerated to 600+/-200km/s as they traveled to the distant tail. The ion temperature inside plasmoids was 4.5+/-2keV in the near and middle tail, and then rapidly decreased to 2+/-1keV from the middle to the distant tail region. The ion temperature in the distant tail was 2 times higher than the values deduced previously. Typical plasmoid dimensions were estimated to be 10RE(length)×40RE(width)×10RE(height) in the middle and distant tail. The energy carried by each plasmoid was ~2×1014J in the middle tail, half of which was lost from the middle to the distant tail. Inside plasmoids, the thermal energy flux exceeded the bulk energy flux and Poynting flux. The energy released tailward in the course of a substorm was estimated to be roughly 1015J.

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