The source, statistical properties, and geoeffectiveness of long‐duration southward interplanetary magnetic field intervals

Abstract

Geomagnetic activity is strongly controlled by solar wind and interplanetary magnetic field (IMF) conditions, especially the southward component of IMF (IMF Bs). We analyze the statistical properties of IMF Bs at 1 AU using in situ observations for more than a solar cycle (1995–2010). IMF Bs events are defined as continuous IMF Bs intervals with varying thresholds of Bs magnitude and duration and categorized by different solar wind structures, such as magnetic cloud (MC), interplanetary small‐scale magnetic flux rope, interplanetary coronal mass ejection without MC signature (ejecta), stream interacting region, and Shock, as well as events unrelated with well‐defined solar wind structures. The statistical properties of IMF Bs events and their geoeffectiveness are investigated in detail based on satellite and ground measurements. We find that the integrated duration and number of Bs events follow the sunspot number when B z   6 h, B z   3 h, B z  < −10 nT) do not always trigger magnetic storms. Key Points The total duration and number of Bs events follow sunspot number as Bz < ‐5 nT In great Bs events 53% are related to MC and 10% are related with Ejecta Bs events with similar duration and value, Earth's responses could be differentPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106708/1/jgra50817.pd