Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm52a0531n&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM52A-0531
Physics
2752 Mhd Waves And Instabilities, 2788 Storms And Substorms
Scientific paper
Previous studies have shown that the plasmaspheric cavity mode resonance is a plausible mechanism for Pi2 pulsations. Fast mode waves emitted from a substorm onset region will bounce back and forth between two boundaries (the ionosphere and the plasmapause) and will be radially trapped, if the wave normal is nearly perpendicular to the boundaries. This is likely to occur near the midnight meridian where substorms are thought to initiate. It is expected that waves would not be trapped effectively on the flanks where the waves make oblique incident on the boundaries, resulting in no appearance of Pi2 pulsations. However, Pi2 pulsations are global phenomena observed at local times far from local midnight. The longitudinal structure of the cavity mode resonance is yet to be investigated. In the present study we focus on a Pi2 pulsation that occurred at 0538 UT on September 20, 1995, because two satellites (ETS-VI and EXOS-D) and ground stations located from low-latitude (L~1.5) to high-latitude (L~12) made observations at 07-10 MLT. Magnetic field data from equatorial and low-latitude stations (L<1.5) at 02 MLT and 15 MLT were also available. This data set provided us with a unique opportunity to investigate the Pi2 pulsation on the morning side in great detail and to examine its longitudinal structure. We found that all ground stations observed a Pi2 pulsation. The ETS-VI satellite at L=6.3 observed a Pi2 pulsation that had nearly the same period and waveform as the ground Pi2 pulsation. The Pi2 pulsation detected by the ETS-VI satellite was dominated by the parallel and radial components, indicating a fast mode wave. Plasma wave observations by the EXOS-D satellite places the plasmapause at L=6.8. From these results, we suggest that the plasmaspheric cavity mode resonance can be established even on the morning side and is a plausible mechanism for the Pi2 pulsation. It was also found that low-latitude Pi2 pulsations were observed globally and showed no phase differences among stations, indicating that the plasmaspheric cavity mode is rather uniform in longitude.
Milling David K.
Miyoshi Yasunobu
Morioka Akira
Nose Mikiha
Sutcliffe Peter R.
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