Multipoint observations of a Pi2 pulsation on morningside: The 20 September 1995 event

We investigated a Pi2 pulsation that occurred at 0538 UT on 20 September 1995, using data from ground stations and the ETS-VI and EXOS-D satellites. Since ground stations at L = 1.45 - 12.6 and the two satellites were located at 7-10 hours of magnetic local time (MLT), we could investigate characteristics of the morning side Pi2 pulsation in detail. We also examined geomagnetic field data from equatorial and low-latitude {L ≤ 1.5) stations at 0200 MLT and 1500 MLT. Our findings include the following: (1) Pi2 pulsations on the morning side were observed over a wide range of L (L < 6.1) with almost identical period (T - 70 s) and waveforms; (2) the ETS-VI satellite located above the geomagnetic equator at L = 6.3 observed a Pi2 pulsation that had nearly the same period and waveforms as the ground Pi2 pulsation; (3) the Pi2 pulsation observed by ETS-VI appeared in the compressional and radial components; (4) phase lag between the compressional and radial components was ∼180° (5) the ground-to-satellite phase lag was ∼180° (∼0°) for the X component and the compressional (radial) component; (6) the EXOS-D observation placed the plasmapause location at L = 6.8, across which ground Pi2 pulsations changed their characteristics; and (7) no phase delay was found between low-latitude Pi2 pulsations observed around 0700 MLT, 0200 MLT, and 1500 MLT. From these results we concluded that the morning side Pi2 pulsation was caused by the plasmaspheric cavity mode resonance and that its longitudinal structure was rather uniform. Copyright 2003 by the American Geophysical Union.