American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 381727 bytes)

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A2, 1020, doi:10.1029/2001JA000197, 2002

Toroidal wave frequency at L = 6–10: Active Magnetospheric Particle Tracer Explorers/CCE observations and comparison with theoretical model

Kazue Takahashi

Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA


Richard E. Denton

Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA


Dennis Gallagher

Space Science Department, NASA Marshall Space Flight Center, Huntsville, Alabama, USA


Abstract

Magnetospheric standing Alfvén waves are guided along the ambient magnetic field, and their frequency depends on the mass density of the plasma distributed along the field lines. These properties allow us to use Alfvén waves to map time-dependent phenomena between space and ground and to estimate the mass density. In this paper we present a statistical study of the spatial variation of the fundamental frequency fT1 of toroidal-mode standing Alfvén waves in the L range from 6 to 10, where L indicates the maximum geocentric distance on the field line. The data used for this analysis are energetic particle flux anisotropy (proxy of transverse electric field) and magnetic field measurements from the Active Magnetospheric Particle Tracer Explorers /Charge Composition Explorer (CCE) spacecraft. Using CCE data covering 4 years, we obtained ∼5000 20-min intervals containing a clear signature of toroidal waves. The median fT1 is 6–10 mHz at L = 7 and decreases to 4–8 mHz at L = 9. The frequency tends to be lower at noon than at midnight. The observed frequencies are compared with numerically derived frequencies using an empirical mass density model [ Gallagher et al., 2000 ] and a magnetic field model [ Tsyganenko, 1989 ]. We found a good agreement for 1200–2400 magnetic local time (MLT) but a large discrepancy near 0300 MLT. This may indicate that the flux tubes at this local time are more heavily loaded than specified in Gallagher et al.'s [2000] model.

Published 7 February 2002.

Index Terms: 2730 Magnetospheric Physics: Magnetosphere—inner; 2731 Magnetospheric Physics: Magnetosphere—outer; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2752 Magnetospheric Physics: MHD waves and instabilities.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 381727 bytes)

Citation: Takahashi, K., R. E. Denton, and D. Gallagher (2002), Toroidal wave frequency at L = 6–10: Active Magnetospheric Particle Tracer Explorers/CCE observations and comparison with theoretical model, J. Geophys. Res., 107(A2), 1020, doi:10.1029/2001JA000197.