RPI/IMAGE plasma and magnetic signatures of solar-wind/magnetosphere interactions

Robert F. Benson, Vladimir A. Osherovich, Joseph Fainberg, James L. Green, 
Scott Boardsen, Leonard N. Garcia, Nikolai Tsyganenko, Bodo W. Reinisch


The magnetospheric electron number density and the magnetic-field strength near
8 RE increased dramatically during the large disturbance of 31 March 2001. These
parameters were determined with high accuracy from the plasma resonances
stimulated by the Radio Plasma Imager (RPI) on IMAGE near apogee. The disturbed
values were compared with magnetospheric magnetic-field and electron-density
models; good agreement was found with the former but not the latter. The
magnetospheric measurements were expressed in terms of the ratio of the electron
plasma frequency to the electron cyclotron frequency which, for an isotropic
plasma, corresponds 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 index QI which is
equivalent to the ratio of the solar-wind magnetic pressure to the solar-wind
ram pressure. These non-dimensional quantities have fundamental meanings in the
solar-wind MHD regime and in the relation between electric and magnetic forces
on electrons in the magnetosphere. Fluctuations in these solar-wind and
magnetospheric fundamental parameters during the large 31 March 2001 storm were
found to be highly correlated (87%) with a magnetospheric time lag of about
three hours.

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Spring Joint Assembly, American Geophysical Union, Baltimore, Maryland, U.S.A., 
23-26 May 2006