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Ann. Geophys., 17, 674-681, 1999
www.ann-geophys.net/17/674/1999/
© European Geosciences Union 1999
A slow mode wave as a possible source of Pi 2 and associated particle precipitation: a case study
O. Saka1,2, O. Watanabe2, K. Okada2, and D. N. Baker3
1Department of Physics, Kurume National College of Technology, Kurume , Japan
E-mail: saka@ges.kurume-nct.ac.jp
2Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
3Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA
Abstract. An intensification of auroral luminosity
referred to as an auroral break-up often accompanies the onset of geomagnetic
pulsation (Pi 2) at the dip-equator. One such auroral break-up occurred at 2239
UT on 16 June, 1986, being accompanied by weak substorm activity (AE~50 nT)
which was recorded in all-sky image of Syowa Station, Antarctica (66.2°S, 71.8°E
in geomagnetic coordinates). The associated Pi 2 magnetic pulsation was detected
by a fluxgate magnetometer in the afternoon sector at the dip-equator (Huancayo,
Peru; 1.44°N, 355.9° in geomagnetic coordinates; 12.1°S, 75.2°W in
geographic coordinates; L=1.00). In spite of the large separation of the
two stations in longitude and latitude, the auroral break-up and subsequent
luminosity modulation were seen to be correlated with the wave form of the
ground Pi 2 pulsation. This occurred in such a way that the luminosity maximum
was seen to occur at the phase of maximum amplitudes of Pi 2 wave form. We argue
that the observed correlation could be interpreted as indicating a Pi
2-modulation of a field-aligned acceleration of the low energy electrons that
may occur near the equator of the midnight magnetosphere.
Key words. Magnetospheric physics (auroral phenomena;
energetic particles · precipitating; MHD waves and instabilities)
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