Physics
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997jgr...102..127n&link_type=abstract
Journal of Geophysical Research, Volume 102, Issue A1, p. 127-140
Physics
41
Magnetospheric Physics: Energetic Particles, Precipitating, Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Magnetospheric Physics: Polar Cap Phenomena, Magnetospheric Physics: Solar Wind/Magnetosphere Interactions
Scientific paper
Various polar cap configurations have been proposod as typical for northward interplanetary magnetic field conditions (IMFBz>0), including that (1) a central region empty of plasma sheet precipitation and arcs remains even after several days of profound magnetic quiet; (2) the polar cap is routinely closed for northward IMF; (3) the polar cap is open, with arcs and polar rain interspersed; and (4) the polar cap is closed, but that arcs separated by no precipitation are spread throughout the polar cap. We have studied eight cases of Bz>0 intervals using DMSP precipitating particle data and high time resolution (15.36 s) IMF data under a variety of conditions. It turns out that all of the first three proposed configurations can occur, but each under a specific set of circumstances. When Bz>0 and Bz~|By| continuously, the polar cap maintains a central finite open region void of precipitation. When Bz>|By| for about 4 hours, the polar cap completely closes, with plasma sheet precipitation across the entire polar cap, and no significant gaps in precipitation. Because the rate at which dayside merging can open flux (~105Wb/s) greatly exceeds the quiet time rate of flux closure (which we estimate to be ~7×103Wb/s), the polar cap proves to be highly dynamic, with southward turnings of about 6-7 min sufficient to balance extended intervals without merging. For this reason, it is comparatively rare that the polar cap completely closes, because even entire days with profound magnetic quiet generally include brief southward fluctuations in Bz. Finally, the configuration of polar cap arcs separated from the oval by several degrees of void or polar rain is created only for Bz<0 after a prolonged or intense interval of Bz>0.
Galland Kivelson Margaret
Meng Ching I.
Newell Patrick T.
Xu Dingan
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