European Geosciences Union, Annales Geophysicae, 10(21), p. 2031-2041, 2003
DOI: 10.5194/angeo-21-2031-2003
Full text: Download
Recent simultaneous observations of cusp structures with Polar, FAST and Interball revealed remarkably similar features at spacecraft crossing the cusp. Such stable cusp structures could be observed up to several hours only during stable solar wind conditions. Their similarities led to the conclusion that for such conditions large-scale cusp structures are spatial structures related to a global ionospheric convection pattern and not the result of temporal variations in reconnection parameters. With the launch of the Cluster fleet we are now able to observe precipitating ion structures in the cusp with three spacecraft and identical instrumentation. The orbit configuration of the Cluster spacecraft allows for delay times between spacecraft of about 45 min in crossing the cusp. The compact configuration of three spacecraft at about the same altitude allows for the analysis of cusp structures in great de-tail and during changing solar wind conditions. Cluster observations on 25 July 2001 are combined with SuperDARN radar observations that are used to derive a convection pattern in the ionosphere. We found that large-scale cusp structures for this Cluster cusp crossing are in agreement with structures in the convection pattern and conclude that major cusp structures can be consistent with a spatial phenomenon. ; We acknowledge the use of ISTP KP database. Solar wind observations were provided by K. Ogilvie at NASA/GSFC (Wind/SWE), magnetic field observations were provided by R. Lepping at NASA/GSFC (Wind/MFI). The work at Lockheed Martin was supported by NASA contracts NAS5-30302, NAG5-3596 and NAG5-12218. The work at the Max-PlanckInstitut fur Aeronomie was supported by DLR under contract 50 ¨ OC 8903 0 (Cluster-CIS). We would like to thank the SuperDARN PIs (W. A. Bristow, P. Dyson, R. A. Greenwald, T. Kikuchi, M. Lester, M. Pinnock, N. Sato, G. Sofko, J.-P. Villain and A. D. M. Walker) for providing the coordinated cluster support radar modes which were running during this spacecraft conjunction. ; Peer-reviewed ; Publisher Version