Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh22e11p&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SH22E-11
Other
2164 Solar Wind Plasma, 2169 Sources Of The Solar Wind, 7509 Corona, 7827 Kinetic And Mhd Theory
Scientific paper
Since the mean free path of the solar particles l increases rapidly with the radial distance, there is an exobase level between 1.5 and 10 Rs where l becomes larger than the density scale height. Exospheric models have been developed above this exobase level, assuming that the charged particles of the solar corona move without collisions in the gravitational, electric and interplanetary magnetic fields, along trajectories determined by their energy and pitch angle at the exobase. In the early exospheric models, the exobase altitude was located within 5-10 solar radii where the total potential energy is a monotonic decreasing function for the protons, and a monotonic increasing function of the radial distance for the electrons. These exospheric models fitted rather satisfactorily the distribution of density and bulk speed observed in the slow solar wind that is emerging from equatorial streamers; however, these zero-order kinetic models were unable to predict fast solar wind speeds in excess of 500 km/s. The aim of this study is to show that exospheric models can be extended to account for the fast solar wind originating in coronal holes. Since the temperature and density in coronal holes are much lower than in the other regions of the corona, the altitude of the exobase is much lower than in equatorial streamers. Deep in the solar corona, the gravitational force is larger than the ambipolar electric force acting on the protons. Most of the protons are trapped in the gravitational potential well up to a radial distance r max(= 3-6)\ Rs where the electric force becomes larger than the gravitational force and accelerates the protons outwards. We will present a new kinetic exospheric model of the solar wind for the case when the total potential energy of the protons has a maximum (i.e. is non monotonically decreasing with the altitude). We will show that the solar wind is accelerated to higher bulk velocities when the exobase level is located below r max. This brings us closer to resolution of the pending issue of the acceleration mechanism for the fast solar wind, without additional energy and momentum deposition at high altitude in the corona.
Lamy Herve
Lemaire Joseph
Maksimovic Milan
Pierrard Viviane
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