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ISTP

>AGU Spring'97

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<font size=+3><b> AGU Spring Meeting 1997 </b></font><br>
<font size=+2><i>Abstracts </i></font>


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Cusp Energetic Particle Events Discovered by POLAR Spacecraft
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Jiasheng Chen, Theodore A. Fritz, R. B. Sheldon, H. E. Spence,
W. N. Spjeldvik, J. F. Fennell, S. Livi
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More than 30 cusp energetic particle (CEP) events were detected by the
Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) on
board the POLAR spacecraft in 1996. All of these events were associated with
a decrease in the magnitude of the local magnetic field measured by the
Magnetic Field Experiment (MFE) on POLAR.

<p>
The CEP events showed six interesting features: (1) They were all
detected in the day-side at high latitude near apogee; (2) their energies
were as high as 4.5 MeV; (3) an individual CEP event could last for hours;
(4) the event-averaged intensity of 1-200 KeV/e Helium was anticorrelated
with the magnitude of the local geomagnetic field; (5) such an anticorrelation
did not exist for 0.5-4.5 MeV helium; and (6) a seasonal variation was
found for both the occurrence rate and the intensity of the CEP events with
a maximum in August and September. The observed high charge state of helium
and oxygen ions in the CEP events indicates a solar source for these
particles. A possible explanation is that the energetic helium ions were
energized from lower energy helium by a local acceleration mechanism
associated with the high-altitude day-side cusp. These observations
represent a potential $discovery$ of a major acceleration region of
the magnetosphere.


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Last Updated: 03/05/97
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