The geo-effectiveness of interplanetary small-scale magnetic flux ropes

The geo-effectiveness of Interplanetary small-scale magnetic flux ropes (ISMFRs) are studied using multiple satellites (ACE, WIND, Geotail, Cluster, THEMIS, and geosynchronous spacecraft) and ground magnetometers. We identified 16 ISMFR events during 2007-2008 that had in situ observations of the near-Earth upstream solar wind in addition to observations from ACE and Wind at 1 AU, and observations from multiple spacecraft in the inner magnetosphere. All the upstream solar wind (and in many cases magnetosheath) satellite observations showed very similar flux rope signatures indicating that the flux rope propagates from 1 AU through the bow shock. Thirteen of the 16 events were associated with substorm activity while nine of them appeared to trigger isolated substorm onsets. Combined with earlier published databases of ISMFRs from 1995 to 2005, we also examined the geo-effectiveness using 1-min AE/AL indices. We found more than half of these events (73/141) were associated with substorms, while the rest were associated with quiet geomagnetic activity periods. Of the 73 substorm-related ISMFRs, 32 events had IMF B-z polarity signatures from south to north (SN), 31 from north to south (NS), and 10 were identified as B-y bipolar signature events. A superposed epoch analysis indicates that the timing of the substorm activity related to the ISMFRs is different between SN- and NS-events. Most of the ISMFRs associated with quiet geomagnetic activity were either B-y bipolar signature events or accompanied with complex B-z and B-y signatures. This study demonstrates that ISMFR with IMF B-z polarity signatures drive substorms, but not geomagnetic storms. (C) 2013 Elsevier Ltd. All rights reserved.