Origin of bright umbral dots in sunspots
Abstract
'Bright umbral dots' are investigated on the basis of a model in which they are considered the result of an instability in deep sunspot layers. A mathematical model of convective instability in the presence of a magnetic field is analyzed to obtain an overall picture of the excitation, development, and decomposition of the structures. These stages are delineated: raising of matter into a low-magnetic cavity resulting from the formation of a convective cell in deep layers of a sunspot; convective transfer of energy into the cavity, which sustains the brightness of the structure; decreases in the temperature gradient of the cavity and in the convective energy and strengthening of the magnetic field, which cuts off the influx of energy from below; gradual deexcitation and decomposition of the bright structures. The lifetime of the structures is briefly noted along with the possible use of this mechanism to determine the fine structure of the magnetic field of a sunspot.
- Publication:
-
Soviet Astronomy
- Pub Date:
- June 1975
- Bibcode:
- 1975SvA....18..758O
- Keywords:
-
- Convective Heat Transfer;
- Fine Structure;
- Magnetohydrodynamic Stability;
- Sunspots;
- Umbras;
- Astronomical Models;
- Benard Cells;
- Brightness;
- Convection Currents;
- Energy Transfer;
- Luminous Intensity;
- Mathematical Models;
- Photosphere;
- Solar Magnetic Field;
- Solar Physics