34th Solar Physics Division Meeting, June 2003
Session 7 Photosphere and Chromosphere I
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[7.04] Influence of Photospheric Magnetism and Dynamics on Chromospheric K-line Emission

J. K. Lawrence, A. C. Cadavid, D. Miccolis (California State University, Northridge), T. E. Berger (Lockheed Martin Solar and Astrophysics Laboratory), A. Ruzmaikin (Jet Propulsion Laboratory/Caltech)

We analyze a unique 9 hr sequence of near simultaneous, high resolution and high cadence G-band and K-line SVST solar filtergrams together with magnetograms of lower cadence and resolution. We focus on a region of the solar surface that includes both internetwork and network. We examine how the (temperature minimum/chromospheric) CaII K-line and (photospheric) G-band intensities, their temporal fluctuations and their coherence and phase relations, with each other and with magnetic fluctuations, change as we progress from weak magnetic fields (internetwork) to intermediate and strong fields (network).

As the background level of flux is increased, sudden photospheric downflow events can create long-lived, compact (i.e. network) magnetic elements. For weak magnetic fields the K-line and G-band intensity signals show an oscillatory component with period centered on 4 min. As we pass to strong fields, the K-line signal shifts to a 5 min period while the G-band signal fades, presumably due to dissociation of the CH radical. The K-line and G-band signals are coherent and nearly in-phase. They are both coherent with fluctuations of the magnetic field. For weak field the magnetic signal leads the intensity signals by 90\circ in phase. For intermediate and strong fields the magnetic signal trails the intensities by 110\circ. We interpret this as a transition from acoustic standing waves with weak, passive magnetic field to a slow mode trapped magnetoacoustic wave. For intermediate magnetic field we find, in addition to the coherent waves, that G-band fluctuations at frequencies above the acoustic cutoff (period < 3.5 min) are associated with magnetic fields and with K-line emission at periods > 3.5 min. This suggests the presence of flux tube waves excited by rapid photospheric perturbations.

This work was supported by grants NSF-ATM 9987305 and NASA-NAG5-10880. The SVST is operated by the Swedish Royal Academy of Sciences at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.


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