Radiating current sheets in the solar chromosphere

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 F_R emitted by individual sheets is 4.9 × 10⁵-4.5 × 10⁶ergcm^-2s^-1, to be compared with the observed chromospheric emission rate of 10⁷ergcm^-2s ^-1. Essentially all emission is from regions with thicknesses 0.5-13km containing the neutral sheet. About half of F_R 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 2000-3000K higher than in the surrounding plasma. The Joule heating flux F_J exceeds F_R 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 F_J . The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized.