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Large deviations of the magnetic field from the Parker spiral in CRRs: Validity of the Schwadron model
Author(s) -
Smith Edward J.
Publication year - 2013
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/jgra.50098
Subject(s) - physics , solar wind , magnetic field , wind speed , heliospheric current sheet , spiral (railway) , computational physics , field line , coronal hole , field (mathematics) , mechanics , astrophysics , coronal mass ejection , meteorology , mathematical analysis , mathematics , quantum mechanics , pure mathematics
A difference in solar wind speed inside and outside a Coronal Hole Boundary (CHB) causes the field and solar wind to expand rapidly with distance to form a Corotating Rarefaction Region (CRR). In the Parker model, field lines inside the CRR form spirals determined by the local solar wind speed. Observationally, however, CRR fields often diverge from the Parker spiral by tens of degrees and in a more radial direction. In a model developed by Schwadron (2002), in addition to the velocity gradient, the field lines rotate differentially across the CHB. The solar wind speed then varies along the field lines rather than remaining constant as in the Parker model. The plausibility of the model is supported by calculations using nominal model parameters that reproduce the systematic deviations from the Parker spiral. The present study establishes the validity of the model by comparing observations of nine CRRs between 1 and 4 AU with model predictions. Estimates are obtained for the width, velocity gradient, differential velocity of the CRR, and the transit time of the magnetic field. These parameters are obtained at the surface near 10 solar radii where the pressure of the coronal magnetic field first becomes balanced.