HR: 11:05h
AN: SM41D-04    [PDF]
TI: The Role of Post-shock Streams and Sheath Regions in Driving Magnetospheric Activity
AU: * Huttunen, E
EM: Emilia.Huttunen@helsinki.fi
AF: University of Helsinki Department of Physical Sciences, P.O.Box 64, Helsinki, 00014 Finland
AU: Koskinen, H E
EM: Hannu.E.Koskinen@helsinki.fi
AF: University of Helsinki Department of Physical Sciences, P.O.Box 64, Helsinki, 00014 Finland
AU: Koskinen, H E
EM: Hannu.E.Koskinen@helsinki.fi
AF: Finnish Meteorological Institute Geophysical Research, P.O.Box 503, Helsinki, 00101 Finland
AB: Post-shock streams and sheath regions are efficient drivers of magnetic disturbances in the Earth's magnetosphere. Characteristics for these structures are high solar wind dynamic pressure and fluctuations in the solar wind electric field. We present statistics indicating that post-shock streams and sheath regions caused almost the half of intense magnetic storms (Dst $<$ -100 nT) during the six-year interval 1997-2002, covering rising, maximum and early declining phases of solar cycle 23. For example the third largest storm of the present solar cycle (determined by the Dst index), that took place on Apr 6-7, 2000, was caused by a sheath region whereas the magnetic cloud appears to have missed the Earth almost entirely. Apart from causing a substantial fraction of large Dst storms, post-shock streams and sheath regions seem to drive more strongly the high-latitude activity than magnetic clouds. We compare in more detail the evolution of two intense magnetic storm periods: One event, Apr 17-18, 2001, was caused by sheath region fields and the other, Apr 21-22, 2001, was driven by a magnetic cloud. We have investigated the geomagnetic response using various magnetic indices. The different behavior of the indices during these two storms suggests the different response of magnetospheric current systems at low and high-latitudes.
DE: 2111 Ejecta, driver gases, and magnetic clouds
DE: 2139 Interplanetary shocks
DE: 2778 Ring current
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Storms and substorms
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting