Open AccessAre coronal holes the only source of fast solar wind at solar minimum?
Author(s) -
Hu Y. Q.,
Habbal S. R.,
Chen Y.,
Li X.
Publication year - 2003
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2002ja009776
Subject(s) - coronal hole , physics , solar wind , helmet streamer , interplanetary magnetic field , corona (planetary geology) , coronal loop , nanoflares , magnetopause , geophysics , polar wind , polar , atmospheric sciences , field line , dipole model of the earth's magnetic field , coronal mass ejection , magnetohydrodynamics , astronomy , magnetic field , astrobiology , quantum mechanics , venus
A two‐dimensional (2‐D) MHD model of an Alfvén‐wave‐driven solar wind in the heliospheric meridional plane is presented whereby the consequences of a magnetic field distribution at the Sun that digresses from the standard dipole structure, often used in 2‐D MHD models, are explored. The latitudinal distribution of open magnetic flux is specified at the solar surface, with a clear distinction between the polar coronal hole and the neighboring quiet Sun. The region of strictly closed magnetic structures at the coronal base is limited in latitude to ±30°. Alfvén waves are assumed to emanate from the solar surface above 30° latitude so as to open the field lines anchored there, as well as heat and accelerate the solar wind. The field lines anchored at the solar surface below 30° latitude, where the plasma is thermally conductive, remain closed, resulting in the formation of the helmet streamer astride the solar equator. The solution obtained is characterized by a helmet streamer in magnetostatic equilibrium, centered at the solar equator, and a steady solar wind outside. With the assumption that the contribution of the polar coronal hole and the quiet Sun to the interplanetary magnetic flux is evenly split between them during solar minimum, a fast wind solution is obtained that matches the latitudinal distribution of the solar wind parameters observed by Ulysses and SOHO and extends from the pole to 9° latitude. The larger fraction (≈60%) of the fast wind (above 30° latitude at 1 AU) emerges from the polar coronal hole, while the remainder is associated with the quiet Sun. While the actual fraction of the fast solar wind originating from polar coronal holes relies on an accurate estimate of the contribution of the open magnetic flux from polar coronal holes to the total IMF flux, this model shows that extending the source of open magnetic flux at the Sun beyond the traditionally assumed polar coronal holes can readily account for the latitudinal distribution of fast wind measured by Ulysses at solar minimum.