Solar Wind Streams of Different Types and High-Latitude Substorms

Abstract

The effects of different large-scale solar wind structures on magnetospheric substorms at high geomagnetic latitudes are studied. Two types of high-latitude substorm disturbances are considered: substorms observed in quiet conditions, when the auroral oval contracts and shifts towards high latitudes (contracted oval substorms, or polar substorms), and those observed in disturbed conditions, when the auroral oval expands (expanded oval substorms, or expanded substorms). Ground-based magnetic observations from the Scandinavian IMAGE network are compared with the OMNI solar wind database and the catalog of large-scale solar wind phenomena (ftp://ftp.iki.rssi.ru/omni/). The study involves the following types of solar wind streams: (1) high-speed streams from coronal holes (FAST); (2) interplanetary manifestations of coronal mass ejections, i.e., magnetic clouds (MCs) or EJECTA; and (3) plasma compression regions ahead of these streams, i.e., corotating interaction regions (CIRs) and SHEATH. The study includes 186 polar and 202 expanded substorms in 1995, 1996, 1999, and 2000. It is shown that ~75% of expanded substorms are observed in FAST streams or plasma compression regions ahead of these streams (CIRs), and only ~18% of such substorms are observed in interplanetary manifestations of coronal mass ejections EJECTA and in SHEATH compression regions. While ~67% of polar substorms are observed in SLOW streams, ~19% of such substorms have been recorded in SHEATH and EJECTA but only against the background of a slow solar wind.