UCL Discovery

Abstract

Using coordinated observations from the Cluster, DMSP and ESR radar, high-altitude cusp was investigated for a time period characterized by four fast reversals of the IMF B (Z). On February 12, 2003, Cluster was flying sunward at duskside over the Northern Hemisphere, across the high-altitude northern cusp twice. Both the two crossings are during steady northward IMF interval, whereas ion fluxes detected during the time period are quite different. The cusp in the first crossing is a "typical" northward-IMF one, with short-lived ion injections of evident "reversed" dispersion signatures. In the second crossing, however, the cusp appears to be a region reminiscent of the Stagnant Exterior Cusp (SEC). In addition, evident upward-flowing O+ ion bursts, possibly original from polar ionosphere, are also detected during the second cusp crossing, together with enhancement of trapped magnetospheric-like electron fluxes. We suggest that the SEC-like cusp is likely on newly closed field lines, which were first reconnected (being opened) at low latitudes and later reconnected again (being closed) poleward of the northern cusp.