Fine-scale magnetic effects on p-modes and higher frequency acoustic wavesin a solar active region

Citation
Jh. Thomas et Dch. Stanchfield, Fine-scale magnetic effects on p-modes and higher frequency acoustic wavesin a solar active region, ASTROPHYS J, 537(2), 2000, pp. 1086-1093
Citations number
23
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004-637X → ACNP
Volume
537
Issue
2
Year of publication
2000
Part
1
Pages
1086 - 1093
Database
ISI
SICI code
0004-637X(20000710)537:2<1086:FMEOPA>2.0.ZU;2-K
Abstract
We present results from a 5 hr time series of simultaneous high-resolution measurements of oscillations in the photosphere and the chromosphere on fin e spatial scales for a rapidly evolving solar active region and examine the ir relation to the vector magnetic field. The photospheric oscillations are determined from Doppler shifts in the Zeeman-insensitive spectral line Fe I 557.6 nm, whereas the chromospheric oscillations are determined from the intensity fluctuations seen in the Ca II K line. The vector magnetic held c ofigurations just prior to and just after the time-series measurements are obtained from the full Stokes inversion of the line profiles of Fe I 630.15 and 630.25 nm. In both the photosphere and the chromosphere, p-mode power is suppressed by the magnetic field, decreasing with increasing field stren gth. At higher frequencies (above the acoustic cutoff) power is also suppre ssed at the highest magnetic field strengths in the photosphere and the chr omosphere but is enhanced in the photosphere in localized patches ("halos") of intermediate field strength surrounding the patches of highest field st rength (as fist reported by Brown et al.). The evidence for similar halos i n the chromosphere (as first seen by Braun et al. and Toner & LaBonte) and their association with the photospheric halos is less clear. We find seismi c evidence, in the forms of suppression of p-mode and higher frequency powe r and a halo of enhanced higher frequency power, for a developing pore prio r to its appearance as a dark patch in Fe I 557.6 nm core intensity. This r esult shows that p-mode power suppression cannot be due primarily to the gr eater transparency of the cooler pore atmosphere.