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Astron. Astrophys. 329, 725-734 (1998)

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1. Introduction

This is the second of two papers analysing cospatial filtergram sequences of the solar photosphere and chromosphere taken with the Swedish Vacuum Solar Telescope on La Palma. Our goal is to search for local relations between waves and fine structure in the quiet photosphere and the overlying chromosphere.

The first paper (Hoekzema et al. 1997; henceforth Paper I) described the science context, the data, the reduction procedures and initial results from wave-amplitude correlations between the photosphere (as imaged in the Fraunhofer G band, called G below) and the chromosphere (Ca II K [FORMULA] filtergrams, called K below). Its main conclusion was that at small spatial scales global and local modulation combine into a complex mix which betrays signatures of local wave excitation by intergranular lanes and displays persistent mesoscale patterning in the chromosphere. The latter may arise from subsurface wave sources and subsurface diffraction. In this paper we extend the analysis by studying such wave and fine structure relations in time-lapse fashion, searching for spatial alignments of different dynamical patterns admitting time delays between them.

The data and the approach are the same as in Paper I. We again combine the Fourier amplitude maps constructed in Paper I with the statistical correspondence factor C introduced there to search for spatial alignments between wave patterning at various periodicities in the photosphere and the chromosphere and the brightness patterning of the photospheric granulation. In this paper we permit considerable time delay between the various waves and features and add the chromospheric internetwork brightness patterning in order to study the occurrence of the so-called Ca II K [FORMULA] grains. The latter form a topic of much debate. It has been reviewed by Rutten & Uitenbroek 1991 and Rutten (1994, 1995, 1996); a summary of pertinent new work is given in Paper I. In brief, the internetwork K [FORMULA] grains portray an acoustic shock phenomenon (Carlsson & Stein 1997), but the nature of the underlying pistons and their patterning remain open issues.

In summary, the small-scale topology patterns addressed here consist of photospheric and chromospheric spatial wave amplitude distributions at 5-min periodicity (photospheric p -modes), 3-min periodicity (chromospheric oscillation) and 2-min periodicity (propagating acoustic waves) and of photospheric and chromospheric brightness patterning (granulation and K [FORMULA] grains). Our searches first chart the time-lapse co-alignment between the brightness structures (Figs. 1-3), then between the various types of waves (Fig. 4), and finally between waves and brightness structures (Figs. 5-6). We again limit the searches to the internetwork regions in our field of view in order to restrict the analysis to non-fluxtube dynamics.

In the next section we summarize the data, the construction of the Fourier maps and the definition of the correspondence factor given in Paper I, and we define the additional brightness classifications used here. The results are given in Sect. 3 and discussed in Sect. 4. The various time-delay correspondence charts provide intriguing hints of piston properties and piston persistence which again point to the importance of mesoscale patterning in the dynamical coupling between the photosphere and the internetwork chromosphere.

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997