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Development and evolution of magnetic fields in active regions on the sun


Chou, Dean-Yi (1987) Development and evolution of magnetic fields in active regions on the sun. Dissertation (Ph.D.), California Institute of Technology.


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The purpose of this thesis is to investigate the development and evolution of magnetic fields in new active regions on the sun. The major observations are digital magnetograms of the line-of-sight component of magnetic fields made with the high sensitivity videomagnetograph at the Big Bear Solar Observatory, and Ha filtergrams with the 1/4 [...] Hα Zeiss filter.

This thesis consists of three themes. First, the separation velocity of emerging magnetic flux is investigated. I measure the separation velocities of opposite polarities of 24 new bipoles, and compare them with the theoretical values estimated by the present theory of magnetic buoyancy. The predicted velocities are higher than those observed. Second, the cooling time scale of growing sunspots is studied. I define the cooling time scale and derive it from the measurements of intensity and magnetic field strength of sunspots. The cooling time scales of the ten growing sunspots studied range from 0.5 to 9 hr. I also estimate the cooling time scale from two models, the Inhibition Model and the Alfven Wave Model, based on linear theory. Both models give cooling times of about 0.05 hr. Third, nonadiabatic effects in convective instabilities in thin flux tubes are examined. I study the convective instabilities in thin flux tubes by including a nonadiabatic term. I find that a flux tube is convectively stable for any field strength.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Zirin, Harold
Thesis Committee:
  • Zirin, Harold (chair)
  • Libbrecht, Kenneth George
  • Cohen, Marshall H.
  • Goldreich, Peter Martin
Defense Date:11 September 1986
Record Number:CaltechETD:etd-09052008-154229
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3345
Deposited By: Imported from ETD-db
Deposited On:10 Sep 2008
Last Modified:26 Dec 2012 02:59

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