Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm52a..01b&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SM52A-01
Physics
2730 Magnetosphere: Inner, 2740 Magnetospheric Configuration And Dynamics, 2764 Plasma Sheet, 2778 Ring Current, 2788 Storms And Substorms
Scientific paper
IMAGE/HENA has imaged more than a two dozens of geomagnetic storms of various strengths since its launch in March 2000. In all storms the peak of the ion differential flux during the mainphase has been concentrated to the midnight and even the post-midnight region. The classical picture of the E-field of the inner magnetosphere has been a sum of the solar wind convectional and corotational field, which produces a pattern with a potential minimum around dusk. Therefore the peak of the ion differential flux was expected to be located around dusk. In this presentation we have investigate 19 relatively long-lasting main phases for storms with a minimum Dst<=-50 nT. The local time location of the peak ion differential flux extends from 22 magnetic local time (MLT) to as far as 06 MLT. The local time angle is found to depend on the clock angle of the interplanetary magnetic field (IMF), with the most severe rotation towards dawn occuring when IMF Bz is strongly negative and IMF By is strongly positive. The morphology of the ion distribution is about the same in the entire 10-200 keV range, which suggests that this pattern can be explained in terms of a strong (1-10 mV/m) electric field at L<5, that focus the ions to the post midnight sector by ExB drift. Substorm injections during the main phase decay away during ~1 in the 27-60 keV range, which suggests that the ions exit the magnetopause around dusk or afternoon local time. Strong E-fields in the inner magnetosphere has been suggested by in-situ observations by CRESS and ground-based radar observations by the Millstone Hill facility (J. Foster, Haystack Observatory, MIT, MA). We present kinetic model runs by M. -C. Fok (this conference) and M. Liemohn and A. Ridley (this conferene) that self consistently calculates the E-field set up by the closure of the partial ring current in the low-latitude ionosphere, where the conductivity is low. The potential drop in the ionosphere therefore becomes high, which then feeds back out into the equatorial magnetosphere. We briefly discuss the effects of stagnation of the earthward when it reaches a region where the magnetic drift cancels the electric drift.
C:son Brandt Pontus
DeMajistre Robert
Fok M.-
Liemohn Michael
Mitchell Donald G.
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