Association of solar wind proton flux extremes with pseudostreamers

Abstract

We investigate the characteristics and solar origins of a subpopulation of the solar wind that possesses extreme values of proton flux. Ulysses observations including solar wind magnetic flux, proton flux, number density and velocity, and ionic composition are examined in this study. We find that the departures of solar wind proton flux from its constancy occur for time intervals leading up to and encompassing the past two solar minima, and the extreme-proton-flux wind possesses the following characteristics: (1) it generally originates from sources middle-distant from the Heliospheric Current Sheet (HCS); (2) it is associated with a broad range of velocities and electron temperatures but excludes very fast/cold wind; (3) it exhibits anticorrelation between electron temperature and proton velocity, as does the rest of the solar wind; (4) it has extreme proton density values relative to the rest of the solar wind; and (5) the extreme-high-proton-flux wind has radial component of open magnetic flux (Br) greater than the rest of the solar wind, and both extreme-high and extreme-low wind do not possess the lowest values of Br flux. Comparing with SOHO EIT 195 Å coronal images, we find the observed extreme-proton-flux wind has temporal and spatial coincidence with the appearance of low-latitude coronal holes present in the recent two solar minima; the magnetic field lines extrapolated by the Potential Field Source Surface model confirm there are coronal pseudostreamer structures involved. So we propose that these extreme-proton-flux winds can be associated with mid- to low-latitude coronal holes and "pseudostreamer" structures. Key Points Extreme-proton-flux solar wind was seen at middle latitudes in two solar minima. This wind has unusual properties compared with the rest of the wind. This wind can be associated with ©2013. American Geophysical Union. All Rights Reserved.