Magnetic Fields and Supergranule Velocity Fields on the Quiet Sun

Citation

Wang, Haimin (1988) Magnetic Fields and Supergranule Velocity Fields on the Quiet Sun. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1cja-6j65. https://resolver.caltech.edu/CaltechETD:etd-09092008-111823

Abstract

I have carried out detailed study on the quiet sun magnetic fields and super-granule velocity fields. This thesis consists of 6 themes. 1. I studied the statistical properties of quiet sun magnetic fields, including size distribution, evolution, flux budget of magnetic flux elements, and the magnetic diffusion constant. From the observations, I derived that the magnetic diffusion constant is ≤150 km²/sec in the quiet region. I found that cancelling features and Ephemeral Regions are major sources of magnetic flux disappearance and replenishment. 2. I studied the supergranule velocity fields. Supergranule vertical velocities have a r.m.s. speed of 0.03 km/s. By observing the evolution of individual supergranule cells, I found that the average lifetime of supergranules is ≥50 hours. 3. I measured the contrast of faculae near the solar limb. The measurements show no obvious contrast increase or decrease near the solar limb. The observation fits neither the "hot wall" nor "hot cloud" fluxtube model. 4. I measured the separation velocities of new bipoles. The observed values are several times smaller than the values estimated by the theory of magnetic buoyancy. 5. I applied the local correlation tracking technique to BBSO Videomagnetogram data and detected an approximate radial intranetwork flow pattern. 6. I studied the relationship between magnetic fields and convection velocity fields. I found that ephemeral regions have a light tendency to emerge at or near the boundaries of supergranules; supergranules have the same scale, correlation lifetime and mean horizontal speed in the enhanced network region as in the mixed polarity quiet sun; the velocity of moving magnetic features that surround sunspots is consistent with the direct Doppler measurement.

Thesis Files