Kinetic Models of the Solar Wind: Achievements and Fundamental Questions

Details Kinetic Models of the Solar Wind: Achievements and Fundamental Questions Kinetic Models of the Solar Wind: Achievements and Fundamental Questions

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008espm...12.3.68p&link_type=abstract

"12th European Solar Physics Meeting, Freiburg, Germany, held September, 8-12, 2008. Online at http://espm.kis.uni-freiburg.de/,

Physics

Scientific paper

Recent kinetic models of the solar corona and of the solar wind will be presented with emphasis on the characteristics of the particle velocity distribution function (VDF). ULYSSES and WIND have observed that the VDF of the solar wind particles deviate significantly from Maxwellians. Using exospheric collisionless models based on the solution of Vlasov equation, we show that the presence of suprathermal electrons increases the electrostatic potential and then accelerates the solar wind to higher bulk velocities. This happens especially in the coronal holes where the number density of the particles is low.
The acceleration of minor ions in the solar wind will also be presented. Due to their different masses and charges, heavy solar ions provide invaluable information on the physical mechanisms responsible for the heating of the corona and for the solar wind acceleration. In exospheric models, the heavy ions are accelerated to high bulk velocities at large radial distances if their coronal temperatures are more than proportional to their mass. Such heating can be obtained by the velocity filtration effect that accounts for the dispersion of ion velocity increasing with altitude in the corona. The kinetic filtration theory predicts indeed ion coronal temperatures which are more than proportional to the mass of the ions, with a small correction for the charge state. No other assumption on the existence and spectrum of MHD or ion-acoustic waves in the corona is then needed to be postulated.
We will present also the effects of the Coulomb collisions with kinetic solar wind models based on the solution of the Fokker-Planck equation. Such models permit to study the transition region between the collision-dominated region in the corona and the collisionless region at larger radial distances.
The differences and complementary aspects of the kinetic and the fluid approaches will also be compared. It is shown that the kinetic approach is required for the description of the low density solar wind plasma.

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