THE SOURCE OF 3 MINUTE MAGNETOACOUSTIC OSCILLATIONS IN CORONAL FANS

Journal Article · Mon Oct 01 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/757/2/160· OSTI ID:22092165

Jess, D. B.; Mathioudakis, M.; Reardon, K. P.; Keys, P. H.; Keenan, F. P. ^[1]; De Moortel, I. ^[2]

---

1. Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN (United Kingdom)
2. School of Mathematics and Statistics, University of St Andrews, St Andrews KY16 9SS (United Kingdom)

We use images of high spatial, spectral, and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the coupling between wave phenomena observed at numerous heights in the solar atmosphere. Analysis of 4170 A continuum images reveals small-scale umbral intensity enhancements, with diameters {approx}0.''6, lasting in excess of 30 minutes. Intensity oscillations of Almost-Equal-To 3 minutes are observed to encompass these photospheric structures, with power at least three orders of magnitude higher than the surrounding umbra. Simultaneous chromospheric velocity and intensity time series reveal an 87 Degree-Sign {+-} 8 Degree-Sign out-of-phase behavior, implying the presence of standing modes created as a result of partial wave reflection at the transition region boundary. We find a maximum waveguide inclination angle of Almost-Equal-To 40 Degree-Sign between photospheric and chromospheric heights, combined with a radial expansion factor of <76%. An average blueshifted Doppler velocity of Almost-Equal-To 1.5 km s{sup -1}, in addition to a time lag between photospheric and chromospheric oscillatory phenomena, confirms the presence of upwardly propagating slow-mode waves in the lower solar atmosphere. Propagating oscillations in EUV intensity are detected in simultaneous coronal fan structures, with a periodicity of 172 {+-} 17 s and a propagation velocity of 45 {+-} 7 km s{sup -1}. Numerical simulations reveal that the damping of the magnetoacoustic wave trains is dominated by thermal conduction. The coronal fans are seen to anchor into the photosphere in locations where large-amplitude umbral dot (UD) oscillations manifest. Derived kinetic temperature and emission measure time series display prominent out-of-phase characteristics, and when combined with the previously established sub-sonic wave speeds, we conclude that the observed EUV waves are the coronal counterparts of the upwardly propagating magnetoacoustic slow modes detected in the lower solar atmosphere. Thus, for the first time, we reveal how the propagation of 3 minute magnetoacoustic waves in solar coronal structures is a direct result of amplitude enhancements occurring in photospheric UDs.

• OSTI ID: 22092165
• Journal Information: Astrophysical Journal, Vol. 757, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
CHROMOSPHERE
COMPUTERIZED SIMULATION
COUPLING
DAMPING
EXTREME ULTRAVIOLET RADIATION
MAGNETOACOUSTIC WAVES
MAGNETOHYDRODYNAMICS
OSCILLATIONS
PARTIAL WAVES
PERIODICITY
PHOTOSPHERE
REFLECTION
RESOLUTION
SUN
SUNSPOTS
THERMAL CONDUCTION
VELOCITY