Monitoring the ion Entry in the High-Altitude Cusp

S. Taguchi, S. Chen, K. Hosokawa, A. Nakao, M.R. Collier, T.E. Moore, M. Fok,
A.S. Yukimatu, and N. Sato


The Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft in the dayside
magnetosphere can detect neutral particles that are emitted in the magnetosheath
flow. A recent study [Taguchi et al. JGR, 2004] has shown that the LENA
emissions observed in the direction of the high-latitude sheath during
relatively high dynamic pressures reflect the cusp indentation in the
magnetopause shape, and that monitoring the cusp motion, which responds to the
large variations of IMF Bz, is possible  using LENA. In this study we report on
simultaneous observations of the high-altitude cusp from IMAGE/LENA and
Polar/TIDE during negative Bz of IMF, and those of the high- and low-altitude
cusps from IMAGE/LENA and the SuperDARN radar for positive Bz. Analyses from the
former observation have shown that the LENA high-latitude sheath emission
consists of two parts: the stable emission at the higher-latitudes (which can be
interpreted as the cusp indentation signal) and the lower-latitude emission, and
that the appearance of this lower-latitude emission coincides with the start of
the Polar observation of the cusp ion entry in similar noon meridian. This
coincidence strongly suggests that the incoming cusp ions charge-exchange with 
the hydrogen exosphere in the entry layer. For the latter observation, we deal
with an event for which emission is strong in LENA_fs field-of-view looking into
the region poleward of the cusp, or the plasma mantle. During this event, the
SuperDARN radar was receiving strong backscattered signals from the very
high-latitude ionosphere. Comparison between the LENA and radar data shows that
the reversed convection is clearly enhanced in the ionosphere in concurrence
with the appearance of the LENA emission, suggesting that LENA can monitor the
ion flow caused by reconnection poleward of the cusp. Detailed characteristics
of the distribution of the emission will be presented, and the spatial extent of
the reconnection region and its temporal variations will be discussed.

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Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004