The floor in the solar wind: Status report

Abstract

Cliver & Ling (2010) recently suggested that the solar wind had a floor or ground-state magnetic field strength at Earth of ∼2.8 nT and that the source of the field was the slow solar wind. This picture has recently been given impetus by the evidence presented by Schrijver et al. (2011) that the Sun has a minimal magnetic state that was approached globally in 2009, a year in which Earth was imbedded in slow solar wind ∼70% of the time. A precursor relation between the solar dipole field strength at solar minimum and the peak sunspot number (SSN MAX) of the subsequent 11-yr cycle suggests that during Maunder-type minima (when SSN MAX was ∼0), the solar polar field strength approaches zero - indicating weak or absent polar coronal holes and an increase to nearly ∼100% in the time that Earth spends in slow solar wind. © 2012 International Astronomical Union.