The interplanetary causes of geomagnetic activity during the 7–17 March 2012 interval: a CAWSES II overview

Abstract

This overview paper presents/discusses the major solar, interplanetary, magnetospheric, and ionospheric features of the CAWSES II interval of study: 7–17 March 2012. Magnetic storms occurred on 7, 9, 12, and 15 March with peak SYM-H intensities of −98 nT, −148 nT, −75 nT (pressure corrected), and −79 nT, respectively. These are called the S1, S2, S3, and S4 events. Although three of the storm main phases (S1, S3, and S4) were caused by IMF B south sheath fields and the S2 event was associated with a magnetic cloud (MC), the detailed scenario for all four storms were different. Two interplanetary features with unusually high temperatures and intense and quiet magnetic fields were identified located antisunward of the MCs (S2 and S3). These features are signatures of either coronal loops or coronal sheaths. A high speed stream (HSS) followed the S4 event where the presumably southward IMF Bz components of the Alfven waves extended the storm “recovery phase” by several days. The ICME-associated shocks were particularly intense. The fast forward shock for the S2 event had a magnetosonic Mach number of ~9.4, the largest in recorded history. All of the shocks associated with the ICMEs created sudden impulses (SI+ s) at Earth. The shocks preceding the S2 and S3 magnetic storms caused unusually high SI+ intensities of ~60 and 68 nT, respectively. Many further studies on various facets of this active interval are suggested for CAWSES II researchers and other interested parties.