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AGU Spring Meeting 1997
High-Latitude Merging and the Orientation of the Interplanetary Magnetic
H E Spence, N U Crooker, and H E Petschek
Boston University Center for Space Physics, Boston, MA, 02215
We investigate properties of magnetic field merging between the
interplanetary magnetic field (IMF) and the geomagnetic field in regions
poleward of the magnetospheric cusp. Recent analysis of POLAR energetic
particle measurements reveals a hot population of ions seen frequently at
high magnetic latitudes when the spacecraft is near apogee ($\sim 8 R_E$
altitude). The polar energetic particle (PEP) events occur at locations
traditionally thought to be connected magnetically with the open fields in
the polar cap. We propose that PEPS may be a reliable signature of
high-latitude merging. The occurrence of PEPs is controlled strongly by
the orientation of the vector IMF. Preliminary analysis indicates that
PEPs occur principally when the IMF has either a strongly northward or
radially outward field. The occurrence probability maximizes when both
conditions are present. We compare the dependence of PEP occurrence on
IMF orientation (measured concurrently by the WIND, IMP8, and/or GEOTAIL
spacecraft) to theoretical models of merging poleward of the cusp. For
example, we investigate the dependence of hemispheric asymmetry in lobe
merging probability on not only the sign of the field components but also
their relative magnitudes, i.e. angle in the x-z plane. Finally, we
discuss aspects of PEP spatial and spectral structure that may be
diagnostic of the merging processes occuring remotely on these high
latitude flux tubes.
Official NASA Contact: Mr. William Mish (email@example.com)
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Last Updated: 03/19/97
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