Ionospheric Signatures of LLBL for Northward IMF S. Chang, S. Chang, D.L. Gallagher, J.F. Spann, S.B. Mende, R.A. Greenwald, and P.T. Newell Enhanced proton auroras associated with the cusp and LLBL have been simultaneously observed by the IMAGE spacecraft during prolonged periods of northward IMF and large solar wind dynamic pressure on 17 and 18 September, 2000. These auroras map to the vicinity of cusp and LLBL at the magnetopause based on the Tsyganenko 96 model. Plasma observed by DMSP that are associated with the aurora confirm the auroral source regions. The cusp ion spectrum has a sharp spectral peak and the typical low-energy ion cutoff consistent with magnetic merging occurring at the high-latitude magnetopause. In contrast, the precipitating ions from the LLBL are of both solar wind and magnetospheric origins. Their energy spectrum is spectrally complete with a very broad spectral width so that there is no indication of recent merging. Ionospheric convection derived from the SuperDARN radar observations for these auroras shows the typical 4-cell pattern for strongly northward IMF. The cusp and LLBL auroras belong to different convection cells. The former appears in the sunward convection region and the latter shows antisunward flow. This pattern persisted for more than 30 min until scattered radar signals were too weak to discern any useful flow pattern. Magnetic field lines in the cusp aurora are open but field lines are most likely closed in the LLBL aurora. Because of the antisunward convection for the LLBL aurora, it is unlikely that the LLBL was formed by closing the sunward-convecting open cusp field lines in one hemisphere after another high-latitude merging at the other hemisphere. It remains a possibility that wave particle interaction at the magnetopause layer can account for the formation of the LLBL. _______________ Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004