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Ann. Geophys., 21, 2281-2292, 2003
www.ann-geophys.net/21/2281/2003/
© European Geosciences Union 2003
Energetic particle counterparts for geomagnetic pulsations of Pc1 and IPDP types
T. A. Yahnina1, A. G. Yahnin1, J. Kangas2, J. Manninen2, D. S. Evans3, A. G. Demekhov4, V. Yu. Trakhtengerts4, M. F. Thomsen5, G. D. Reeves5, and B. B. Gvozdevsky1
1Polar Geophysical Institute, Apatity, Murmansk region, Russia
2Sodankylä Geophysical Observatory, Sodankylä, Finland
3NOAA Space Environmental Center, Boulder, Colorado, USA
4Institute of Applied Physics, Russian Academy of Sciences, Nizhniy Novgorod, Russia
5Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract. Using the low-altitude NOAA
satellite particle data, we
study two kinds of localised variations of energetic proton
fluxes at low altitude within the anisotropic zone equatorward
of the isotropy boundary. These flux variation types
have a common feature, i.e. the presence of precipitating protons
measured by the MEPED instrument at energies more
than 30 keV, but they are distinguished by the fact
of the presence or absence of the lower-energy component as
measured by the TED detector on board the NOAA satellite.
The localised proton precipitating without a low-energy component
occurs mostly in the morning-day sector, during
quiet geomagnetic conditions, without substorm injections at
geosynchronous orbit, and without any signatures of
plasmaspheric plasma expansion to the geosynchronous distance.
This precipitation pattern closely correlates with ground-based
observations of continuous narrow-band Pc1 pulsations
in the frequency range 0.1–2 Hz (hereafter Pc1). The
precipitation pattern containing the low energy component occurs
mostly in the evening sector, under disturbed geomagnetic conditions,
and in association with energetic proton injections
and significant increases of cold plasma density at
geosynchronous orbit. This precipitation pattern is associated
with geomagnetic pulsations called Intervals of Pulsations
with Diminishing Periods (IPDP), but some minor part
of the events is also related to narrow-band Pc1. Both
Pc1 and IPDP pulsations are believed to be the electromagnetic ion-cyclotron
waves generated by the ion-cyclotron instability
in the equatorial plane. These waves scatter energetic protons
in pitch angles, so we conclude that the precipitation patterns
studied here are the particle counterparts of the
ion-cyclotron waves.
Key words. Ionosphere
(particle precipitation) – Magnetospheric physics
(energetic particles, precipitating) – Space plasma
physics (wave-particle interactions)
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