Characteristics of magnetohydrodynamic oscillations observed with the Michelson Doppler Imager

Citation
Aa. Norton et al., Characteristics of magnetohydrodynamic oscillations observed with the Michelson Doppler Imager, ASTROPHYS J, 518(2), 1999, pp. L123-L126
Citations number
9
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004637X → ACNP
Volume
518
Issue
2
Year of publication
1999
Part
2
Pages
L123 - L126
Database
ISI
SICI code
0004-637X(19990620)518:2<L123:COMOOW>2.0.ZU;2-S
Abstract
We report on the spatial distribution of the magnetogram oscillatory power and the phase angles between velocity and magnetogram signals as observed w ith the Michelson Doppler Imager. The data set is 151." 25 x 151." 25, cont aining the sunspot from 1997 December 2 with a temporal sampling interval o f 60 s and spatial sampling of 0." 605. The simultaneously observed continu um intensity and surface velocity accompany the magnetic information, We fo cus on three frequency regimes: 0.5-1.0, 3.0-3.5, and 5.5-6.0 mHz, correspo nding roughly to timescales of magnetic evolution, p-modes, and the 3 minut e resonant sunspot oscillation. Significant low-frequency magnetogram power is found in lower flux pixels, 100-300 G, in a striking ring with filament ary structure surrounding the sunspot. The 5 minute magnetogram power peaks in extended regions of flux that measure 600-800 G. The 3 minute oscillati on is observed in the sunspot umbra in pixels whose flux measures 1300-1500 G, Phase angles of approximately -90 degrees between velocity and magnetic flux in the 3.0-3.5 and 5.5-6.0 mHz regimes are found in regions of signif icant cross amplitude.