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Session 33 - Dynamics of Solar Magnetic Fields.
Oral session, Tuesday, June 11
Wisconsin Center,
Solar magnetic flux elements on spatial scales below 350 km (0\arcsec.5) are analyzed using G-Band 4305 ÅCa II K-line, and 4686 Å\ continuum filtegrams as well as Fe I 6302 Å\ and 5250 Å\ magnetograms acquired nearly simultaneously at the Swedish Solar Vacuum Telescope on La Palma. Spatial resolution is below 0\arcsec.3 in the majority of images. Phase-diversity image restoration is applied to yield a 180 frame (78 minute) image set in which nearly every frame exhibits 0\arcsec.2 spatial resolution. Image processing algorithms are developed which successfully segment the magnetic elements from the surrounding granulation for analysis.
The FWHM of magnetic elements demarcated by G-band bright points in disk-center plage is log-normally distributed with a modal value of 220 km and an average value of 250 km. Average disk center contrast of magnetic elements in the G-band is 31% with maximum values frequently exceeding 70% relative to the quiet-Sun average. Simulataneous 4686 Å\ continuum contrast is 2 to 3 times lower. The average G-band contrast of magnetic elements shows no size dependency over a range of 150---600 km in diameter. G-band bright points occur without exception on sites of isolated magnetic flux concentrations or peninsular concentrations extending from larger concentrations of flux; isolated magnetic flux concentrations are found without associated G-band bright points. Magnetic elements demarcated by G-band bright points occupy no more than 1---2% of plage and active network regions by area at any one time. Magnetic elements move in the intergranular flowfield at speeds from 0.5 to 5 km sec^-1. The RMS speed is 2.4 km sec^-1 over an average range of 2100 km (3\arcsec). Continual fragmentation and merging of magnetic elements is the normal evolutionary mode for small-scale magnetic elements. The time scale for the dynamics is approximately 6--8 minutes, but significant morphological changes occur on time scales as short as 100 seconds. Analysis of the tracks of individual elements yields a diffusion coefficient of 224.8\pm0.2 \itkm^2\itsec^-1. Indications of anomolous diffusivity consistent with diffusion on a fractal geometry are found.
This research was supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University and NASA contract NAS8-39747 and independent research funds at Lockheed-Martin.
