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Coronal magnetic field topology and source of fast solar wind
Author(s) -
Guhathakurta M.,
Sittler E.,
Fisher R.,
McComas D.,
Thompson B.
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl010662
Subject(s) - coronal hole , solar wind , physics , corona (planetary geology) , polar wind , coronal mass ejection , latitude , magnetopause , polar , geophysics , flux (metallurgy) , astrophysics , magnetohydrodynamics , atmospheric sciences , magnetic field , astronomy , astrobiology , venus , metallurgy , materials science , quantum mechanics
We have developed a steady state, 2D semi‐empirical MHD model of the solar corona and the solar wind with many surprising results. This model for the first time shows, that the boundary between the fast and the slow solar wind as observed by Ulysses beyond 1 AU, is established in the low corona. The fastest wind observed by Ulysses (680–780 km/s) originates from the polar coronal holes at 70°–90° latitude at the Sun. Rapidly diverging magnetic field geometry accounts for the fast wind reaching down to a latitude of ±30° at the orbit of Earth. The gradual increase in the fast wind observed by Ulysses, with latitude, can be explained by an increasing field strength towards the poles, which causes Alfvén wave energy flux to increase towards the poles. Empirically, there is a direct relationship between this gradual increase in wind speed and the expansion factor, f , computed at r >20 R ⊙. This relationship is inverse if f is computed very close to the Sun.