Conjugate observations of ENA signals in the high-altitude cusp and proton auroral spot in the low-altitude cusp with IMAGE spacecraft

Dayside proton auroral spots in the ionosphere are frequently observed by the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft. On 28 April 2001 (0500-0630 UT), when the solar wind density was about 10 cm- 3 and IMF was northward except for a few short periods, FUV observed proton auroral spots in the cusp ionosphere. The intensification of the proton auroral spot was simultaneous with ENA signals observed by the Low Energy Neutral Atom (LENA) imager on IMAGE also from the direction of the high-altitude cusp. If the primary source of the LENA cusp signal were the proton injection caused by reconnection, then the LENA signal in the high-altitude cusp and the FUV spot in the low-altitude cusp should have a common source. The magnetic field line tracing with the Tsyganenko-96 model shows that the possible source location of the LENA cusp signal maps on the proton auroral spot, and the temporal variations of both intensities also show a correlation. During the interval of interest a brief period has been identified in which the proton aurora moves toward the pre-noon side and the direction of the LENA cusp signal moves poleward. Considering the solar wind variations for this event, we have interpreted these motions as being due to the detached reconnected flux tubes created by a brief southward tilting of the IMF, and not the shift of the reconnection point which is often invoked for the motion of the FUV spot in the cusp. Detailed characteristics about the correspondence between the LENA signal and the FUV spot are presented, and the field line geometry for the detached reconnected flux tube will be discussed.