Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm52a0541s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM52A-0541
Physics
2736 Magnetosphere/Ionosphere Interactions, 2740 Magnetospheric Configuration And Dynamics, 2752 Mhd Waves And Instabilities, 2768 Plasmasphere, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
A combination of simultaneous measurements from high-altitude, low-altitude and ground-based instruments is used to explore the large-scale coherence of ULF pulsations in the magnetosphere. Periodogram analysis of the time series measured at various regions of the magnetosphere reveals that the energy in the pulsations is consistently concentrated in a few discrete peaks. These peaks are found simultaneously in the electrojet intensifications, geosynchronous dipolarizations and energetic particle injections, plasma and magnetic field oscillations in the plasma sheet, and magnetic field oscillations in the tail lobes. The evolution of the large-scale correlation of the magnetosphere is tracked by examining the correlation matrix of the time series filtered into various frequency bands, over successive time intervals. We define a measure of coherence at each time interval as the correlation length that gives the best fit to an exponential decay of correlation with increasing separation. When the correlation length is examined over a range of geomagnetic activity levels, it becomes apparent that substorm expansion onsets establish a high level of coherence (long correlation lengths) in the magnetosphere at all ULF frequencies considered (0.5-6.0 mHz). However, as the substorm progresses into a state of expanded oval and plasma sheet, long correlation lengths are observed only at certain discrete frequency bands. In the example analyzed, there was one band extending between 1.5 and 2.0 mHz. The discrete frequency bands of long correlation length appear to be dependent of the solar wind forcing, which was observed at a lower frequency (below ~1.0 mHz).
Cosgrove Russell B.
Sanchez Ennio R.
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