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Ann. Geophys., 20, 1763-1767, 2002
www.ann-geophys.net/20/1763/2002/
© European Geosciences Union 2002
Location of Pc 1–2 waves relative to the magnetopause
R. E. Denton, J. LaBelle, and X. Zhu
Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA
Correspondence to: R. E. Denton
(richard.denton@dartmouth.edu)
Abstract. Spacecraft-borne and
ground-based magnetometers frequently detect magnetospheric micropulsations in
the period range 0.2–10 s, termed Pc 1–2, and attributed to electromagnetic
ion cyclotron waves driven by temperature anisotropy (T^
> T ||). Previous surveys of
Pc 1 occurrence locations have been limited to L < 9. We
present AMPTE/IRM observations of the distribution of Pc 1 waves out to the
magnetopause, for a limited region of MLT = 10–14. The probability of wave
occurrence Pwav is large (> 0.15) between L = 7–12,
peaking at L = 8–10 (Pwav ~ 0.25). When the L-value
is normalized to the magnetopause position Lmp, however, the
highest probabilities of Pc 1 wave occurrence are close to the magnetopause,
with Pwav ~0.25 for Lnorm = L/Lmp
= 0.8–1.0. These results are consistent with increased convective growth rate
at large L and with the greater effect of magnetosphere compression
close to the magnetopause. On the other hand, we only directly observe magnetic
field compression for at most about 25% of the wave events.
Key words. Magnetospheric physics (magnetospheric
configuration and dynamics; MHD waves and instabilities; plasma waves and
instabilities)
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