Enhanced high-altitude polar cap plasma and magnetic field values in response to the interplanetary magnetic cloud that caused the great storm of 31 March 2001: A case study for a new magnetospheric index

Details Enhanced high-altitude polar cap plasma and magnetic field values in response to the interplanetary magnetic cloud that caused the great storm of 31 March 2001: A case study for a new magnetospheric index Enhanced high-altitude polar cap plasma and magnetic field values in response to the interplanetary magnetic cloud that caused the great storm of 31 March 2001: A case study for a new magnetospheric index

Jun 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jgra..11206247o&link_type=abstract

Journal of Geophysical Research, Volume 112, Issue A6, CiteID A06247

Physics

5

Magnetospheric Physics: Polar Cap Phenomena, Magnetospheric Physics: Ring Current, Magnetospheric Physics: Solar Wind/Magnetosphere Interactions

Scientific paper

The magnetospheric electron number density and the magnetic field strength near 8 R E over the polar cap increased dramatically after the arrival of an interplanetary magnetic cloud on 31 March 2001. These parameters were determined with high accuracy from the plasma resonances stimulated by the Radio Plasma Imager (RPI) on Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) near apogee during both quiet (30 March 2001) and disturbed (31 March 2001) days. The quiet day and disturbed day values were each compared with magnetospheric magnetic field and electron density models; good agreement was found with the former but not the latter. The magnetospheric response was also expressed in terms of the ratio of the electron plasma frequency f pe to the electron cyclotron frequency f ce , which is proportional to the ratio of the electron gyroradius to the Debye radius. Simultaneous Wind measurements of the solar wind magnetic field strength, speed, and plasma density were used to calculate the solar wind quasi-invariant QI. This index is equivalent to the ratio of the solar wind magnetic pressure to the solar wind ram pressure or to the inverse of the magnetic Mach number squared. These nondimensional quantities, QI and f pe /f ce , have fundamental meanings in the solar wind MHD regime and in the relation between electric and magnetic forces on electrons in the magnetosphere, respectively. During the large 31 March 2001 storm, IMAGE was at the right place at the right time so as to enable comparisons between RPI f pe /f ce and Wind QI determinations. Both QI and f pe /f ce formed maxima during 6-hour observing intervals during this storm that were found to be highly correlated (87%) with a magnetospheric time lag of about 3 hours for f pe /f ce . These results, based on a detailed case study of this important event, suggest that the plasma parameter f pe /f ce may serve as a useful magnetospheric index.

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