Article

Influence of Photospheric Magnetic Fields and Dynamics on Chromospheric K-Line Emission

We analyze a 9 hr sequence of simultaneous, high-resolution, high-cadence G-band and K-line solar filtergrams plus magnetograms of lower cadence and resolution. Images include both network and internetwork. The magnetic and filtergram intensities, their fluctuations, and relative phases change with progressive strengthening of local magnetic field. At increased flux levels, sudden photospheric downflows create long-lived magnetic elements. For weak magnetic fields the K-line and G-band intensities include an oscillatory component with period 4 minutes. For stronger fields, the K-line period shifts to 5 minutes, while the G-band fluctuations fade due to dissociation of their source, the CH radical. These K-line and G-band fluctuations, whose periods are longer than the acoustic cutoff, are coherent and in phase. They also are coherent with fluctuations of the magnetic field. Weak-field magnetic fluctuations lead the intensity fluctuations by a phase shift of 90 . Strong-field magnetic fluctuations trail the intensities by 100 . These are interpreted as standing waves in the photosphere and low chromosphere. Another class of G-band fluctuations, with periods shorter than the acoustic cutoff, is associated both with stronger magnetic fields and with enhanced K-line emission with fluctuations longer than the cutoff period. This suggests waves excited by rapid photospheric perturbations and propagating up along magnetic flux tubes.

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