Small-scale topology of solar atmosphere dynamics : II : granulation, K2v grains and waves

We continue studying the small-scale topology of dynamical phenomena in the quiet-sun internetwork atmosphere throug statistical estimation of the co-location probability of different fine-structure elements and wave modes.In this paper we chart spatial alignments between the granular brig tness structuring of the photosphere, Ca ii K 2V brig tness patterns in the c romosphere,and wave amplitude patterns in bot regimes as a function of time delay between the occurrences of the various features.These charts confirm the presence of excess 2-4 min waves above dark intergranular lanes, the absence of ex cess 5 min waves above bright granules,the absence of expected alignments between photospheric and chromosp eric wave patterning,and the broad-band nature of Ca II K 2V grain formation.In addition,they show significant alignments at large time delays that seem to be regulated by mesoscale patterning and pattern migration

Ultraviolet jets and bright points in the solar chromosphere : II : statistical correlations

We use HRTS{VI rocket observations of the solar chromosphere to search for relationships between high-Dopplershift \jets" observed in the CI lines near = 156 nm and internetwork \bright points" observed in the = 160 nm continuum, in sequel to the analysis by Cook et al. (1996) which failed to find a direct connection between these phenomena. We now use the same data to establish statistical correlations between CI Dopplershift and 160 nm brightness modulation in internetwork areas. These mean relations emerge only after extensive spatial averaging and have small amplitude, but are definitely significant. They show that both CI Dopplershift and 160 nm brightness participate in oscillatory behavior with three-minute periodicity and mesoscale (8 Mm wavelength) as well as small-scale (1.4 Mm wavelength) spatial patterning. We find spatial and temporal phase relations between Dopplershift and brightness that confirm that jets and bright points should not be interpreted as isolated entities. Rather, they are chromospheric manifestations, with much pattern interference, of the oscillatory acoustic shock dynamics in the internetwork which also cause Ca II K2V grains. Additional small-scale modulation is present which we attribute to waves with f-mode character

Small-scale topology of solar atmosphere dynamics : III : granular persistence and photospheric wave amplitudes

We use a superb five-hour sequence of 900 solar images taken at La Palma to study long-duration persistence in the solar granulation,in the context of the longlived "intergranular holes" discovered by Roudier et al. (1997)and th e contention that these mark sites of convective downflow plumes.We develop a procedure to locate "persistency regions" that contain granular brightness maxima or minima over extended periods (up to 45 min),while allowing for lateral drifts due to horizontal flows. Statistical evaluation of the co-location probability for different pixel classes is first used to quantify the likelihood of long-term stationarity for different granular brightness classes and for the persistency regions,and then to evaluate the amount of preferential alignment,at different frequencies and time delays,between excessive Fourier modulation and granular brightness and persistence. The results support the existence of long-lived intergranular oles.There is large persistency difference between the brig test and the darkest features; some of the latter ave location memories as long as two ours.In addition, the darkest intergranular features are found to be sites of enhanced Fourier modulation in the 3-min acoustic regime,improving earlier results throug much higher statistical significance.However,the persistency regions containing intergranular oles do not seem to produce the excess acoustic emission that would be expected above down flow plumes

Ultraviolet jets and bright points in the solar chromosphere: I : search for one-to-one relationships

Ultraviolet spectrograms and spectroheliograms of the solar chromosphere are used to test the suggestion (Dere et al. 1986, Rutten & Uitenbroek 1991a) that bright points observed at h = 1600 Å, chromospheric jets observed in CI lines near h = 1560 Å, and Ca II K2V bright points are associated with each other and that they are all manifestations of the same wave interaction in the non-magnetic chromosphere. We search for spatio-temporal connections between 1600 Å bright points and CI blue jets using data from the HRTS VI rocket mission, comparing 1600 Å spectroheliograms and a co-spatial CI Dopplershift map on a pixel-by-pixel basis. We find no direct evidence for spatial co-location of bright points and jets, not for instantaneous correspondence and also not when allowing for phase delays as long as three minutes. Also, the average brightness evolution and its rms uctuation are not obviously different between sites of large CI blueshift and the remaining surface

Small-scale topology of solar atmosphere dynamics I: wave sources and wave diffraction

We study the small-scale topology of dynamical phenomena in the quiet-sun internet w ork atmosphere,using short-duration Fourier analysis of high-resolution filtergram sequences to obtain statistical estimates for the co-location probability of different fine-structure elements and wave modes. In this initial paper w e concentrate on the topology of short-duration Fourier amplitude maps for the photosphere and the simultaneously observed o verlying chromosphere. We find that these maps portray acomplex mix of global modes and locally excited w aveswhich necessitates a statistical approach. Variousaspects including mesoscale patterning indicate the presence of subsurface w avesources and of subsurface w avediffraction by convective inhomogeneities

Do quasi-regular structures really exist in the solar photosphere? I. Observational evidence

Two series of solar-granulation images -- the La Palma series of 5 June 1993 and the SOHO MDI series of 17--18 January 1997 -- are analysed both qualitatively and quantitatively. New evidence is presented for the existence of long-lived, quasi-regular structures (first reported by Getling and Brandt (2002)), which no longer appear unusual in images averaged over 1--2-h time intervals. Such structures appear as families of light and dark concentric rings or families of light and dark parallel strips (``ridges'' and ``trenches'' in the brightness distributions). In some cases, rings are combined with radial ``spokes'' and can thus form ``web'' patterns. The characteristic width of a ridge or trench is somewhat larger than the typical size of granules. Running-average movies constructed from the series of images are used to seek such structures. An algorithm is developed to obtain, for automatically selected centres, the radial distributions of the azimuthally averaged intensity, which highlight the concentric-ring patterns. We also present a time-averaged granulation image processed with a software package intended for the detection of geological structures in aerospace images. A technique of running-average-based correlations between the brightness variations at various points of the granular field is developed and indications are found for a dynamical link between the emergence and sinking of hot and cool parcels of the solar plasma. In particular, such a correlation analysis confirms our suggestion that granules -- overheated blobs -- may repeatedly emerge on the solar surface. Based on our study, the critical remarks by Rast (2002) on the original paper by Getling and Brandt (2002) can be dismissed.Comment: 21 page, 8 figures; accepted by "Solar Physics

DOT Tomography of the Solar Atmosphere VII. Chromospheric Response to Acoustic Events

We use synchronous movies from the Dutch Open Telescope sampling the G band, Ca II and Halpha with five-wavelength profile sampling to study the response of the chromosphere to acoustic events in the underlying photosphere. We first compare the visibility of the chromosphere in Ca II H and Halpha, demonstrate that studying the chromosphere requires Halpha data, and summarize recent developments in understanding why this is so. We construct divergence and vorticity maps of the photospheric flow field from the G-band images and locate specific events through the appearance of bright Ca II H grains. The reaction of the Halpha chromosphere is diagnosed in terms of brightness and Doppler shift. We show and discuss three particular cases in detail: a regular acoustic grain marking shock excitation by granular dynamics, a persistent flasher which probably marks magnetic-field concentration, and an exploding granule. All three appear to buffet overlying fibrils, most clearly in Dopplergrams. Although our diagnostic displays to dissect these phenomena are unprecedentedly comprehensive, adding even more information (photospheric Doppler tomography and magnetograms, chromospheric imaging and Doppler mapping in the ultraviolet) is warranted.Comment: accepted by Solar Physic

Optical depth retrievals from HRSC stereo images

Mars Express is due to arrive in orbit around Mars during the last days of 2003. A primary task of its mission is to map Mars in stereo with the High Resolution Stereo Camera (HRSC) at a spatial resolution of up to 12 m. The Martian atmosphere contains large amounts of dust as well as other aerosols that scatter light and influence the images. Therefore, image analysis requires careful consideration of these atmospheric effects. An essential parameter to consider is the total optical depth. It will be possible to map the optical depth of the Martian atmosphere from HRSC stereo images by analyzing contrast differences. Software for this purpose has been developed at the Max-Planck Institute for Aeronomy in Lindau Germany. We present examples of optical depth-retrievals from airborne HRSC-A images of a region in the French Alps