Physics
Scientific paper
Oct 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11610225a&link_type=abstract
Journal of Geophysical Research, Volume 116, Issue A10, CiteID A10225
Physics
Ionosphere: Particle Precipitation, Magnetospheric Physics: Cusp, Magnetospheric Physics: Magnetic Reconnection (7526, 7835), Magnetospheric Physics: Magnetosphere/Ionosphere Interactions (2431)
Scientific paper
The low-energy neutral atom (LENA) imager on the IMAGE spacecraft can detect energetic neutral atoms produced by ion injection into the cusp through a charge exchange with the Earth's hydrogen exosphere. We examined the occurrence of the LENA cusp signal during positive IMF BZ in terms of the arrival direction and the IMF clock angle $\theta$CA. Results of statistical analyses show that the occurrence frequency is high on the postnoon side when $\theta$CA is between ˜20° and ˜50°. This is ascribed to ion injection caused by cusp reconnection typical of positive IMF BZ. Our results also show that there is another situation of high occurrence frequency, which can be identified with $\theta$CA of ˜30° to ˜80°. When $\theta$CA is relatively large (60°-80°), occurrence frequencies are high at relatively low latitudes over a wide extent spanning both prenoon and postnoon sectors. This feature suggests that the ion injection is caused by reconnection at the dayside magnetopause. Its postnoon side boundary shifts toward the prenoon as $\theta$CA decreases. When $\theta$CA is less than ˜50°, the high occurrence frequency exists well inside the prenoon sector, which is azimuthally separated from the postnoon region ascribed to cusp reconnection. The prenoon region, which is thought due to ion injection caused by dayside reconnection, may explain the recent report that proton aurora brightening occurs in the unanticipated prenoon sector of the northern high-latitude ionosphere for IMF BY > 0 and BZ > 0.
Abe Mitsuko
Collier Michael R.
Moore Thomas Earle
Taguchi Satoshi
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