Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh41a1608k&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH41A-1608
Physics
4455 Nonlinear Waves, Shock Waves, Solitons (0689, 2487, 3280, 3285, 4275, 6934, 7851, 7852), 7507 Chromosphere, 7524 Magnetic Fields, 7827 Kinetic And Mhd Theory, 7859 Transport Processes
Scientific paper
A complete anisotropic, inhomogeneous electrical conductivity tensor, which includes Spitzer, Pedersen, and Hall conductivities is included in an MHD simulation to describe how MHD shock waves may form, propagate, and resistively heat the atmosphere from the photosphere through the chromosphere. The MHD model includes an energy equation. The initial state is defined by FAL density, pressure, and temperature profiles, and by a magnetic field that decreases with height z. The initial magnetic field strength at the photosphere is 500 G. A harmonic magnetic field perturbation with amplitude 250 G and period 30 seconds is applied at the photosphere. Smooth waves are generated at the photosphere that propagate upward and begin to form shock waves near z=350 km. This is the height near which electrons first become magnetized. The shocks become fully formed near the FAL temperature minimum at z=500 km. This is the height where the product of the electron and proton magnetizations first exceeds unity, causing the Pedersen resistivity to begin to rapidly exceed the Spitzer resistivity by orders of magnitude with increasing height. This is also the height at which heating by proton Pedersen current dissipation rapidly increases with height, and rapidly becomes large enough to balance the radiative losses from the chromosphere. The onset of this strong heating is triggered by the onset of electron and proton magnetization near the temperature minimum. The shock thicknesses are ~ ~ 5 km. The shocks are the sites of resistive heating rates as large as 3-10 ergs-cm-3-sec-1 in the chromosphere. The time averaged heating rate over an interval of 162 seconds corresponds to a chromospheric heating flux ~ 2-3 × 106 ergs-cm-2-sec-1. The heating rate increases with driving frequency, and is ∝ B2. These results support the proposition of Goodman (e.g. Goodman 2000, ApJ, 533, 501; Goodman 2004, A&A, 424,691; Kazeminezhad & Goodman 2006, ApJ, 166, 613) that the onset of electron and proton magnetization near the local temperature minimum, and their rapid increase with height causes the rate of proton Pedersen current dissipation to rapidly increase by orders of magnitude with height, creating and maintaining the solar chromosphere, and the chromospheres of solar type stars. This mechanism is not restricted to shock waves. It operates on any current generating MHD process. Such a process must involve currents driven by a combination of induction and convection generated electric fields. Examples are linear waves, and steady convection across magnetic field lines. It is the weakly ionized, strongly magnetized nature of the chromosphere that allows this heating mechanism to be so effective, and that distinguishes the chromosphere from the weakly ionized, weakly magnetized photosphere, and the strongly ionized, strongly magnetized corona. The dominance of proton-neutral H collisions in determining the proton collision frequency is necessary for this Pedersen current dissipation mechanism to be an effective heating mechanism in the chromosphere. This work was supported by Grant ATM 0650443 from the National Science Foundation to the West Virginia High Technology Consortium Foundation.
class="ab'>
Goodman Michael L.
Kazeminezhad Farzad
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