The pressure and energy balance of the cool corona over sunspots.
Abstract
The 22 largest sunspots observed with the Skylab SO55 spectrometer are studied for a relation between their EUV radiation and their umbral size or magnetic classification. The ultimate goal is to determine why the coronal plasma is so cool over a sunspot and how this cool plasma manages to support itself against gravity. Based on the time behavior of the EUV emission, a steady-state model is developed for the pressure and energy balance of the cool coronal-plasma loops over the spots. Analysis of the temperature structure in a typical loop indicates that the loop is exceedingly well insulated from the outside corona, that its energy balance is determined purely by internal heating and cooling processes, and that a heat input of about 0.0001 erg/cu cm per sec is required along the full length of the loop. It is proposed that: (1) coronal material flows steadily across the field lines at the tops of the loops and falls downward along both sides under gravity; (2) the corona is heated by mechanical-energy transport across the very thin transition region immediately over network-cell interiors; and (3) strong magnetic fields tend to inhibit mechanical-energy dissipation in the corona.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1976
- DOI:
- 10.1086/154862
- Bibcode:
- 1976ApJ...210..575F
- Keywords:
-
- Energy Spectra;
- Far Ultraviolet Radiation;
- Plasma Temperature;
- Solar Corona;
- Spaceborne Astronomy;
- Sunspots;
- Apollo Telescope Mount;
- Emission Spectra;
- Energy Distribution;
- Magnetohydrodynamic Stability;
- Pressure Distribution;
- Radiant Flux Density;
- Radiative Transfer;
- Temperature Distribution;
- Thermal Instability;
- Ultraviolet Spectrometers;
- Solar Physics