Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh41a1615s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH41A-1615
Physics
7507 Chromosphere
Scientific paper
The chromosphere is a weakly ionized region with an ionization fraction about one in ten thousand. As the neutral and plasma densities decrease with height, the collision frequencies between the two species decrease. In the upper half of the chromosphere, the Alfven time for a magnetic field perturbation to propagate to the transition region and the ion-neutral collision time are both much shorter than the neutral- ion collision time. Under these conditions, the bulk flow velocity of the plasma can differ from that of the neutrals; collisions between the neutrals and the plasma then become an important mechanism for transferring momentum between neutrals and plasma and converting energy of different types. We study the chromosphere on the basis of a three-fluid (electrons, ions, and neutrals) approach. The physical description includes the three-fluid generalized Ohm's law, Maxwell's equations, the plasma momentum equation, and the neutral momentum equation, thus taking into account collisions among all three species as well as electromagnetic coupling among the charged species. The geometrical configuration in this initial study, however, is highly simplified and is approximated as a localized one-dimensional incompressible flow region with vertical magnetic field but no vertical flow. The system is driven by an assumed change in the tangential (horizontal) flow of plasma at around 1000 km altitude. The plasma flow perturbation distorts the magnetic field, and the distortion propagates upward in the chromosphere to the transition region, while the neutrals respond much more slowly, in the neutral-ion collision time. The difference between plasma and neutral velocities produces collisions between the neutrals and the plasma, with the result that the neutrals are accelerated by the plasma flow and part of the plasma flow kinetic energy is converted to thermal energy of both neutrals and plasma. With a perturbation of ~ 1 km/s, a preliminary estimate gives a heating rate in the chromosphere of order 108 erg cm-2 s-1.
Song Paul
Vasyliūnas Vytenis M.
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