ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Springer Verlag Göttingen, Germany 10.1007/s00585-999-0674-4 A slow mode wave as a possible source of Pi 2 and associated particle precipitation: a case study Saka O. 2 3 1 Watanabe O. 3 Okada K. 3 Baker D. N. 4 Department of Physics, Kurume National College of Technology, Kurume , Japan E-mail: saka@ges.kurume-nct.ac.jp Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA 31 05 1999 17 5 674 681 Copyright: © 1999 O. Saka et al. 1999 © European Geosciences Union 1999 This article is available from https://angeo.copernicus.org/articles/17/674/1999/angeo-17-674-1999.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/17/674/1999/angeo-17-674-1999.pdf

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; <i>L</i>=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.<br><br><b>Key words.</b> Magnetospheric physics (auroral phenomena; energetic particles · precipitating; MHD waves and instabilities)