Distributions of Solar Wind Discontinuity Normals for Different Solar Activity and Solar Wind Types

Abstract

We present a statistical analysis of the interplanetary magnetic field (IMF) discontinuity normals across solar cycle 23 and 24 for different solar wind types. We employ both the Minimum variance analysis (MVA) and Cross-product methods to determine phase front normals using ACE observations. We confirm that most discontinuity normals point earthward and dawnward at longitudes from 180$°$ to 250$°$ and lie between latitudes −40$°$ and 40$°$. A wider range of normals is observed during the solar minimum and declining phases compared to the solar maximum and ascending phases. Discontinuities point strongly northward or southward more frequently during solar minimum than during solar maximum. We categorize the data into four solar wind types, Coronal Mass Ejections-Magnetic Ejecta (CME-ME), CME-SH (Sheath), Stream Interaction Regions (SIR), and Non-CME/Non-SIR for the years 2001–2002 (solar maximum) and 2008–2009 (solar minimum). The discontinuity normals are strongly oriented antisunward during CMEs (CME-MEs and CME-SHs). The distributions during SIRs are similar to those observed in the absence of any particular solar wind type.