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Paper: Characteristics of MHD Oscillations Observed with MDI
Volume: 184, Third Advances in Solar Physics Euroconference: Magnetic Fields and Oscillations
Page: 136
Authors: Norton, A. A.; Ulrich, R. K.; Bush, R. I.; Tarbell, T. D.
Abstract: We report on the spatial distribution of magnetic oscillatory power and phase angles between velocity and magnetic signals as observed with the Michelson Doppler Imager. The dataset is 151.25arcsec x 151.25arcsec containing sunspot from Dec 2, 1997 with a temporal sampling interval of 60 seconds and spatial sampling of 0.605arcsec. Simultaneously observed continuum intensity and surface velocity accompany the magnetic information. We focus on three frequency regimes: 0.5-1.0, 3.0-3.5 and 5.5-6.0 mHz corresponding roughly to timescales of magnetic evolution, p-modes and the 3 minute resonant sunspot oscillation. Significant low frequency magnetic power is found in lower flux pixels, 100-300 Gauss, in a striking ring with filamentary structure surrounding sunspot. Five minute oscillatory magnetic power peaks in extended regions of flux 600-800 Gauss. The 3 minute oscillation is observed in sunspot umbra in pixels whose flux measures 1300-1500 Gauss. Phase angles of -90° between velocity and magnetic flux in the 3.0-3.5 and 5.5-6.0 mHz regimes suggest the MHD oscillations are magnetoacoustic in nature.
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