Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm32c..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM32C-07
Physics
2700 Magnetospheric Physics, 2712 Electric Fields (2411), 2744 Magnetotail, 2760 Plasma Convection, 2788 Storms And Substorms
Scientific paper
The mechanism of particle injection and associated field variation is one of the most fundamental issues regarding magnetic storm. Several recent modeling studies on the storm-time ring current suggest that enhanced convection electric field in the magnetosphere, which is induced by continuous southward IMF, is responsible for steady particle transport into the inner magnetosphere during the storm main phase. On the other hand, the enhanced convection weakens, or ceases after the main phase in response to the decrease of southward IMF, leading to the formation of a relatively symmetric ring current around the Earth during the recovery phase. Although these modeling studies have been employing some electric field models that apply a somewhat strong ( ˜ 1 mV/m), large scale electric field to the region from the near-Earth plasma sheet to the inner magnetosphere on the night side, systematic observational studies have not been made yet to investigate such a large electric field by using in situ measurement performed in the near-Earth plasma sheet. We have examined particle and field observations made by the Geotail spacecraft during magnetic storms to study enhanced convection and the associated electric field that is thought to be a key to govern the particle injection into the ring current. Surprisingly, our preliminary study found no clear evidence for the existence of such a large, steady earthward convection during either the storm main phase or the recovery phase. The observed particle and field properties in the near-Earth plasma sheet are basically classified into the two categories of time intervals: One is governed by stagnant plasmas with small, fluctuating electric fields, and the rest of intervals are dominated by intermittent flow bursts and associated large spikes of the dawn-dusk component of the electric field accompanied by significant increases in the north-south component of the magnetic field. Thus it appears to be nothing but a typical sequence of particle and field variations associated with substorms. These results imply that a continuous earthward particle transport driven by the enhanced convection is not likely to take place from the near-Earth plasma sheet to the ring current region, and that particle injection associated with substorms still plays a major role in the ring current development during storm main phase.
C:son Brandt Pontus
Hayakawa Hisao
Hori Toshihiro
Lui A. T.
Maezawa Kiyoshi
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