Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere

• Published in: Solar physics 2012-09, Vol.280 (1), p.125-136
• Main Authors: Lawrence, J. K., Cadavid, A. C.
• Format: Article
• Language: English
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Fluctuations; Fluid mechanics; Magnetic fields; Physics; Physics and Astronomy; Propagation; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Sun
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-012-0059-9

We study Hinode /SOT-FG observations of intensity fluctuations in Ca ii H-line and G-band image sequences and their relation to simultaneous and co-spatial magnetic field measurements. We explore the G-band and H-line intensity oscillation spectra both separately and comparatively via their relative phase differences, time delays and cross-coherences. In the non-magnetic situations, both sets of fluctuations show strong oscillatory power in the 3 – 7 mHz band centered at 4.5 mHz, but this is suppressed as magnetic field increases. A relative phase analysis gives a time delay of H-line after G-band of 20±1 s in non-magnetic situations implying a mean effective height difference of 140 km. The maximum coherence is at 4 – 7 mHz. Under strong magnetic influence the measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A second coherence maximum appears between 7.5 – 10 mHz. Investigation of the locations of this doubled-frequency coherence locates it in diffuse rings outside photospheric magnetic structures. Some possible interpretations of these results are offered.