Radiative Cooling, Convective Downflows and the Formation of Small-Scale Strong Magnetic Field Structures on the Sun
Abstract
Radiative energy transport has important dynamical consequences for the evolution of gas confined in small-scale magnetic structures on the Sun. The convective collapse process which transforms weak field structures into intense structures of strength in the range 1-2 kG, which eventually form sunspots in the emerging flux regions, is affected by the radiative heating from the surroundings and cooling due to vertical losses. Through a simple analysis of such radiative transfer effects in the diffusion approximation for a thin magnetic flux tube, we show the destabilizing action of vertical radiative losses in the form of an accelerated downflow, thereby verifying theoretically the thermal origin of the convective collapse process, as suggested by Parker (1978). We also perform numerical stability calculations involving the generalised Eddington approximation for radiative transfer and produce size(flux)-strength relations for the solar small-scale magnetic structures. Our results provide a physical explanation for the flux dependent (equivalently size dependent) field strength of the solar small-scale magnetic structures and the two-component (weak intra-network and the strong network) distribution is explained in terms of physical parameters that control the convective collapse process.
- Publication:
-
SOHO-9 Workshop on Helioseismic Diagnostics of Solar Convection and Activity
- Pub Date:
- 1999
- Bibcode:
- 1999soho....9E..16R