Effects of diverging coronal fields on the solar wind expansion

Details Effects of diverging coronal fields on the solar wind expansion Effects of diverging coronal fields on the solar wind expansion

Aug 1976

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976ap%26ss..43...19f&link_type=abstract

Astrophysics and Space Science, vol. 43, Aug. 1976, p. 19-33.

Astronomy and Astrophysics

Astrophysics

2

Magnetic Flux, Magnetohydrodynamics, Solar Corona, Solar Magnetic Field, Solar Wind Velocity, Coulomb Collisions, Magnetic Moments, Plasma Interactions, Velocity Distribution

Scientific paper

The expansion of the solar wind from the corona through divergent magnetic flux tubes is recalculated from the MHD equations with the inclusion of a 'magnetic acceleration term' which arises due to the radial magnetic-field gradient when treating the solar-wind plasma as an ensemble of radially expanding guiding centers. It is assumed that the plasma particles have established magnetic moments and must obey the guiding-center approximation, which is valid in flux tubes with cross sections much larger than a Larmor radius. The magnetic acceleration term in the MHD momentum equation is found to provide the solar wind with an additional outward force that acts in a direction opposite to the gradient of the diverging coronal magnetic field. Two important results of this are that: (1) the solar-wind velocity rises faster to its asymptotic value, implying that velocities at small heliocentric distances are higher than previously assumed, and (2) the shape of the solar-wind velocity-distribution function is determined by the effect of the anisotropy-producing magnetic acceleration term as well as by randomizing Coulomb collisions among the plasma particles. It is demonstrated that these results should be valid for some representative radial flux tubes out to about 0.1 AU.

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