|
|
 |
|
|
Ann. Geophys., 25, 1653-1667, 2007
www.ann-geophys.net/25/1653/2007/
© European Geosciences Union 2007
Observations at geosynchronous orbit of a persistent Pc5 geomagnetic pulsation and energetic electron flux modulations
T. E. Sarris1,2, T. M. Loto'aniu3, X. Li1, and H. J. Singer4
1Lab. for Atmospheric and Space Physics, Univ. of Colorado, Boulder, CO, USA
2Demokritus University of Thrace, Xanthi, Greece
3Dept. of Physics, University of Alberta, Edmonton, Canada
4NOAA Space Environment Center, Boulder, CO, USA
Abstract. A long lasting narrow-band (4–7 mHz) Pc5 fluctuation event at geosynchronous
orbit is presented through measurements from GOES-8 and GOES-10 and the
response of energetic electrons with drift frequencies close to the
narrow-band pulsation frequency is monitored through a spectral analysis of
flux data from the LANL-SOPA energetic electron instrument. This analysis
shows electron flux modulations at the magnetospheric pulsation's frequency
as well as at various other frequencies in the Pc5 range, related to the
particles' drift-frequencies and their harmonics. A drift resonance effect
can be seen, with electron flux modulation becoming more evident in the
energy channels of electrons with drift frequencies closer to the wave
frequency; however no net increase or decrease in energetic electron flux is
observed, indicating that the net energy transfer and transport of electrons
is not significant. This Pc5 event has a long duration, being observed for
more than a couple of days at geosynchronous orbit over several traversals
of the two GOES satellites, and is localized in azimuthal extent. Spectral
analysis shows that most of the power is in the transverse components. The
frequency of the narrow-band event, as observed at geosynchronous orbit
shifts during the time of the event from 7±0.5 mHz to about 4±0.5 mHz.
On the ground, CARISMA magnetometers record no distinct narrow-band
fluctuation in the magnetic field, and neither does Geotail, which is
traversing the outer magnetosphere a few RE further out from
geosynchronous orbit, at the same UT and LT that GOES-8 and -10 observe the
pulsations, suggesting that that there is no connection to external
fluctuations originating in the solar wind. An internal generation mechanism
is suggested, such as could be provided by energetic ring current particles,
even though conclusive evidence could not be provided for this particular
event. Through a statistical study, it is found that this event belongs to a
class of similar events, occurring predominantly in the post-noon region in
the inner magnetosphere.
Full Article in PDF (8059 KB) |
|
|
