Dynamical Phenomena in Sunspots.
Abstract
The reflection of upward and downward propagating Alfven waves in sunspots is studied, in order to assess the possibility of cooling by Alfven waves. Wave reflection is studied by means of a three-layer model of the umbral atmosphere. The results show very strong downward reflection of Alfven waves in the photosphere and low temperature, but only weak upward reflection in the convection zone. Further study of more realistic magneto-atmospheric waves (including the effects of compression and buoyancy) shows strong upward reflection in the convection zone as well as strong downward reflection in the photosphere and low chromosphere. These results tend to rule out significant sunspot cooling by waves. A study of a simple thermal model of a sunspot, based on the concept of partial inhibition of convection, shows that the inhibition mechanism can yield acceptable distributions of surface temperature. The results of this model also show that: (1) the edge of the umbra is sharp, even for deep spots; (ii) deep spots produce weak bright rings, but shallow spots produce intense bright rings in conflict with observations; and (iii) only a shallow surface layer of the sunspot is cool, the rest being warmer than the surroundings. Umbral oscillations in sunspots are studied and identified a resonant response of the umbral atmosphere to forcing by oscillatory convection in the subphotosphere. The full linearized equations for magneto-atmospheric waves are solved numerically for a detailed model of the umbral atmosphere. It is suggested that the Sun's radius and surface temperature vary with the solar cycle due to the variation of total magnetic buoyancy in the convection zone over the cycle of the solar dynamo.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 15, 1980
- Accession Number
- ADA086010
Entities
People
- Alfred Clark Jr.
- John H Thomas
- Mark A. Scheuer
Organizations
- University of Rochester