Monitoring the ion Entry in the High-Altitude Cusp

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.