Radiating Current Sheets in the Solar Chromosphere
Abstract
An MHD model of a hydrogen plasma with flow, an energy equation, NLTE ionization and radiative cooling, and an Ohm's law with anisotropic electrical conduction and thermoelectric effects is used to self-consistently generate atmospheric layers over a 50 km height range. A subset of these solutions contains current sheets and has properties similar to those of the lower and middle chromosphere. The magnetic field profiles are found to be close to Harris sheet profiles, with maximum field strengths ~25-150 G. The radiative flux FR emitted by individual sheets is ~4.9 × 105-4.5 × 106 erg cm-2 s-1, to be compared with the observed chromospheric emission rate of ~107 erg cm-2 s-1. Essentially all emission is from regions with thicknesses ~0.5-13 km containing the neutral sheet. About half of FR comes from sub-regions with thicknesses 10 times smaller. A resolution <~ 5-130 m is needed to resolve the properties of the sheets. The sheets have total H densities ~1013-1015 cm-3. The ionization fraction in the sheets is ~2-20 times larger, and the temperature is ~2000-3000 K higher than in the surrounding plasma. The Joule heating flux FJ exceeds FR by ~4%-34%, the difference being balanced in the energy equation mainly by a negative compressive heating flux. Proton Pedersen current dissipation generates ~62%-77% of the positive contribution to FJ . The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2012
- DOI:
- 10.1088/0004-637X/751/1/75
- arXiv:
- arXiv:1406.1211
- Bibcode:
- 2012ApJ...751...75G
- Keywords:
-
- magnetic fields;
- magnetic reconnection;
- magnetohydrodynamics: MHD;
- plasmas;
- stars: chromospheres;
- Sun: chromosphere;
- Astrophysics - Solar and Stellar Astrophysics;
- Physics - Plasma Physics;
- Physics - Space Physics
- E-Print:
- 29 pages, 11 figures