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

Abstract

[1] 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.

Change of solar wind quasi-invariant in solar cycle 23—Analysis of PDFs

“…While this high correlation was shown to hold at 1 AU, this correlation is also maintained at lower heliospheric distances , and at large distances (Fainberg and Osherovich, 2002). Thus one advantage of using QI is that, as a global parameter, QI follows closely the activity cycle of the Sun with in situ measurements in the heliosphere (Leitner et al, 2005;Osherovich et al, 2007). It was shown by Leitner et al (2009a) that during the recent exceptionally quiet solar cycle minimum the average QI values are lower than in two previous minima (1976 and 1995).…”

Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data

“…They provide convenient ways to represent the plasma environment around the Earth. Empirical models are important for developing physics-based numeric models as well, since they provide baseline predictions against which to measure their performance (Siscoe et al 2004) and against which plasma density variations can be evaluated, particularly during magnetic storms (e.g., Tu et al 2007;Osherovich et al 2007).…”

Polar cap electron density distribution from IMAGE radio plasma imager measurements: Empirical model with the effects of solar illumination and geomagnetic activity

“…Previous investigation based on the radio plasma imager (RPI) [ Reinisch et al , 2000] on the Imager for Magnetopause‐to‐Auroral Global Exploration (IMAGE) satellite [ Burch et al , 2001] have shown that the polar cap electron density N e increases with geomagnetic activity [e.g., Nsumei et al , 2003; Tu et al , 2004, 2007; Osherovich et al , 2007]. The finding from IMAGE RPI observations is consistent with earlier studies using DE 1 and Polar satellite observations, as well as numerical simulations [e.g., Yau et al , 1985; Moore et al , 1999; Schunk and Sojka , 1997].…”