Author name code: brandt ADS astronomy entries on 2022-09-14 author:"Brandt, Peter N." AND aff:"Freiburg" ------------------------------------------------------------------------ Title: Do Long-Lived Features Really Exist in the Solar Photosphere? II. Contrast of Time-Averaged Granulation Images Authors: Brandt, P. N.; Getling, A. V. Bibcode: 2008SoPh..249..307B Altcode: 2008arXiv0802.0204B; 2008SoPh..tmp...64B The decrease in the rms contrast of time-averaged images with the averaging time is compared between four data sets: (1) a series of solar granulation images recorded at La Palma in 1993, (2) a series of artificial granulation images obtained in numerical simulations by Rieutord et al. (Nuovo Cimento25, 523, 2002), (3) a similar series computed by Steffen and his colleagues (see Wedemeyer et al. in Astron. Astrophys.44, 1121, 2004), (4) a random field with some parameters typical of the granulation, constructed by Rast (Astron. Astrophys.392, L13, 2002). In addition, (5) a sequence of images was obtained from real granulation images by using a temporal and spatial shuffling procedure, and the contrast of the average of n images from this sequence as a function of n is analysed. The series (1) of real granulation images exhibits a considerably slower contrast decrease than do both the series (3) of simulated granulation images and the series (4) of random fields. Starting from some relatively short averaging times t, the behaviour of the contrast in series (3) and (4) resembles the t−1/2 statistical law, whereas the shuffled series (5) obeys the n−1/2 law from n=2 on. Series (2) demonstrates a peculiarly slow decline of contrast, which could be attributed to particular properties of the boundary conditions used in the simulations. Comparisons between the analysed contrast-variation laws indicate quite definitely that the brightness field of solar granulation contains a long-lived component, which could be associated with locally persistent dark intergranular holes and/or with the presence of quasi-regular structures. The suggestion that the random field (4) successfully reproduces the contrast-variation law for the real granulation (Rast in Astron. Astrophys.392, L13, 2002) can be dismissed. Title: Dynamics of solar mesogranulation Authors: Leitzinger, M.; Brandt, P. N.; Hanslmeier, A.; Pötzi, W.; Hirzberger, J. Bibcode: 2005A&A...444..245L Altcode: Using a 45.5-h time series of photospheric flow fields generated from a set of high-resolution continuum images (SOHO/MDI) we analyze the dynamics of solar mesogranule features. The series was prepared applying a local correlation tracking algorithm with a 4.8´´ FWHM window. By computing 1-h running means in time steps of 10 min we generate 267 averaged divergence maps that are segmented to obtain binary maps. A tracking algorithm determines lifetimes and barycenter coordinates of regions of positive divergence defined as mesogranules (MGs). If we analyze features of lifetimes ≥1 h and of areas ≥5 Mm{2 we find a mean drift velocity of 304 m s-1 (with ± 1σ variation of 180 m s-1), a mean travel distance of 2.5 ± 1.8 Mm, a mean lifetime of 2.6 ± 1.8 h, and a 1/e decay time of 1.6 h for a total of 2022 MGs. The advective motion of MGs within supergranules is seen for 50 to 70% of the long-lived (≥4 h) MGs while the short-lived ones move irregularly. If only the long-lived MGs are further analyzed the drift velocities reduce to 207 m s-1 and the travel distances increase to 4.1 Mm on average, which is an appreciable fraction of the supergranular radius. The results are largely independent of the divergence segmentation level. Title: Solar Site Survey for the Advanced Technology Solar Telescope. I. Analysis of the Seeing Data Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Streander, K. Bibcode: 2005PASP..117.1296S Altcode: 2005astro.ph..8690S The site survey for the Advanced Technology Solar Telescope concluded recently after more than 2 years of data gathering and analysis. Six locations, including lake, island, and continental sites, were thoroughly probed for image quality and sky brightness. The present paper describes the analysis methodology employed to determine the height stratification of the atmospheric turbulence. This information is crucial, because daytime seeing is often very different between the actual telescope aperture (~30 m) and the ground. Two independent inversion codes have been developed to simultaneously analyze data from a scintillometer array and a solar differential image monitor. We show here the results of applying them to a sample subset of data from 2003 May that was used for testing. Both codes retrieve a similar seeing stratification through the height range of interest. A quantitative comparison between our analysis procedure and actual in situ measurements confirms the validity of the inversions. The sample data presented in this paper reveal a qualitatively different behavior for the lake sites (dominated by high-altitude seeing) and the rest (dominated by near-ground turbulence). Title: The ATST Site Survey Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K. Bibcode: 2005AGUSMSP34A..04H Altcode: The Advanced Technology Solar Telescope (ATST) will be the world's largest aperture solar telescope, and is being designed for high resolution, IR, and coronal research. It must be located at a site that maximizes the scientific return of this substantial investment. We present the instrumentation, analysis and results of the ATST site survey. Two instrumentation sets were deployed at each of six sites to measure seeing as a function of height, and sky brightness as a function of wavelength and off-limb position. Analysis software was developed to estimate the structure function Cn2 as a function of height near the ground, and the results were verified by comparison with in-situ measurements. Additional software was developed to estimate the sky brightness. The statistics of the conditions at the sites were corrected for observing habits and the annualized hours of specific observing conditions were estimated. These results were used to identify three excellent sites suitable to host the ATST: Haleakala, Big Bear and La Palma. Among them, Haleakala is proposed as the optimal location of the ATST, La Palma and Big Bear being viable alternative sites. Title: The first decades of JOSO -- the Joint Organization for Solar Observations Authors: Brandt, Peter N.; Mattig, Wolfgang Bibcode: 2005AcHA...25..240B Altcode: In 1969 a group of leading European solar physicists established the Joint Organization for Solar Observations (JOSO) with the aim to promote international cooperation and to find an outstanding site for a new European solar observatory. After an extensive site test finally in 1979 they found excellent sites on the Canary Islands for the deployment of several national instruments in the framework of the newly founded Instituto de Astrofísica de Canarias. The well co-ordinated thriving international cooperation made the continuation of JOSO desirable even after the fulfilment of the originally planned goals. New fields of cooperation were found, in particular the ground-based support of the SOHO mission. After the fall of the “iron curtain” in 1989 intensive collaboration with the Eastern-European institutes was initiated, and JOSO turned into an enterprise for broad scientific and technological exchange. Title: Families of fragmenting granules and their relation to meso- and supergranular flow fields Authors: Roudier, Th.; Lignières, F.; Rieutord, M.; Brandt, P. N.; Malherbe, J. M. Bibcode: 2003A&A...409..299R Altcode: 3D analysis (x,y,t) of the granular intensity field (11-hour time sequence from the Swedish Vacuum Solar Telescope on La Palma, Canary Islands), demonstrates that a significant fraction of the granules in the photosphere are organized in the form of ``Trees of Fragmenting Granules" (TFGs). A TFG consists of a family of repeatedly splitting granules, originating from a single granule at its beginning. A striking result is that TFGs can live much longer (up to 8 h) than individual granules (10 min). We find that 62% of the area covered by granules belongs to TFGs of a lifetime >1.5 h. When averaged in time, such long-lived TFGs correspond to coherent diverging flows which may be identified as mesogranules. We also find a correlation between the network and the spatial distribution of TFGs. Title: Deriving effective sunspot temperatures from SOHO/VIRGO irradiance measurements. A starspot modelling approach Authors: Eker, Z.; Brandt, P. N.; Hanslmeier, A.; Otruba, W.; Wehrli, C. Bibcode: 2003A&A...404.1107E Altcode: A method is developed to obtain mean effective sunspot temperatures from satellite irradiance deficits. Using a formalism derived from a star spot modelling approach, this method only requires accurate positions and areas of sunspots - but not intensities. The method is applied to SOHO/VIRGO spectral solar irradiance (SSI) at 402, 500, and 862 nm as well as total solar irradiance (TSI) measured during the period 16 July to 17 August 1996, the disk passage of active region NOAA 7981. MDI full disk white-light images are used to extract sunspot positions and areas. First, using the spot pixels, which are identified on MDI images as Is < 0.92, we find the mean effective temperature of NOAA 7981 to be =~ 300 K less than the local photospheric temperature. Because the area is dominated by penumbral pixels, the temperature is close to a value representing the penumbra. Second, separating umbral and penumbral pixels, we obtain a temperature difference of =~ 850 K for the umbra and of =~ 200 K for the penumbra. Finally, if a 5% binning of the spot intensities is applied, a temperature deficit of =~ 1000 K is found for the darkest regions of the spot.

Appendixes A, B are only available in electronic form at http://www.edpsciences.org Title: Recurrence of fragmenting granules and their relation to meso- and supergranular flow fields Authors: Roudier, Th.; Lignières, F.; Rieutord, M.; Brandt, P. N.; Malherbe, J. -M. Bibcode: 2003EAS.....9..371R Altcode: The 3D analysis (x, y, t) of the granulation intensity field (11-hour time sequence from Swedish Vacuum Solar Telescope on La Palma, Canary Islands), demonstrated that the granules in the phostosphere are organized in ``Trees of Fragmenting Granules" (TFGs). A TFG consists of a family of repeatedly splitting granules, issued from one granule at its beginning. A striking result is that TFGs can live much longer (up to 8h10) than individual granules (10 mn). When averaged in time, such long-lived TFGs can be identified to the mesogranules. We also found a correlation between the network and the spatial distribution of TFGs. Title: Evolution and motions of small-scale photospheric structures near a large solar pore Authors: Dorotovič, I.; Sobotka, M.; Brandt, P. N.; Simon, G. W. Bibcode: 2002A&A...387..665D Altcode: The analysis of an 11-hour series of high resolution white light observations of a large pore in the sunspot group NOAA 7519, observed on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary Islands, is described. We used a total of 1782 frames, with average time interval of 22 s. Special attention was paid to the evolution of a filamentary region attached to the pore, to horizontal motions around the pore, and to small-scale morphological changes. The filamentary region was observed to change its structure back and forth between penumbra-like filaments and elongated granules. A clockwise rotation of this region around the center of the pore was detected during the whole observing period. This rotation had angular velocities decreasing with time from 7.6deg h-1 to 2.7deg h-1. Motions inside the filamentary region and around the pore, including penetrations of photospheric granules into the pore, were studied in detail using local correlation and feature tracking algorithms. It was found that the observed filamentary region, although having some typical penumbral features, was different from a normal penumbra. Title: Evolution of Filamentary Structures in and around a Large Solar Pore Authors: Simon, G. W.; Dorotovič, I.; Sobotka, M.; Brandt, P. N. Bibcode: 2002AAS...200.3803S Altcode: 2002BAAS...34..698S We have studied evolution of a filamentary region attached to a pore, horizontal motions around the pore, and small-scale morphological changes, using an 11-hour series of 1782 high resolution white-light images of a large pore in the sunspot group NOAA 7519, acquired on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary Islands. We find that the structure of the region between the large pore and an adjacent micropore was not always filamentary, but varied back and forth in time between a filamentary structure and a granular one. A clockwise rotation, at times exceeding 7 deg/h, of this filamentary region around the center of the pore, was observed during the whole run. Motions of fine structure around and within the pore were studied in detail using local correlation and feature tracking. We conclude that the filamentary region, while it had some typical penumbral characteristics, was different from a normal penumbra. This research has been funded by the USAF Research Lab, and by Emeritus Research Services. Title: Regular structures of the solar photosphere. (Persistence of the granular field and trenching in the brightness relief) Authors: Getling, A. V.; Brandt, P. N. Bibcode: 2002A&A...382L...5G Altcode: The simple procedure of time averaging, when applied to the photospheric brightness field, reveals quasi-regular structures of the photospheric and subphotospheric flows. We use an 8-h sub-set of the series of photospheric images obtained on 5 June 1993 with the Swedish Vacuum Solar Telescope, La Palma. First, the averaged images are far from completely smeared and contain a multitude of bright, granular-sized blotches even if the averaging period is as long as 8 h. This suggests that granules prefer to originate at certain sites, where they emerge repeatedly, and the granular field demonstrates a sort of persistence for many hours. Second, the resulting patterns display relatively regular structures, which can be revealed only if the averaging period is sufficiently long (the optimum seems to lie between 2 and 3 h). The averaged brightness relief is ``trenched'': it comprises systems of concentric rings and arcs as well as straight or slightly wavy lines and systems of parallel strips. The trenching patterns resemble the so-called target patterns observed in experiments on Rayleigh-Bénard convection. In addition, the brightness values at a local averaged-field maximum and at a nearby minimum exhibit a distinct tendency to vary in antiphase. Thus, a previously unknown type of self-organization is manifest in the solar atmosphere, and our findings support the suggestion that granules are associated with overheated blobs carried by the convective circulation. Title: Time-slice diagrams of solar granulation Authors: Müller, D. A. N.; Steiner, O.; Schlichenmaier, R.; Brandt, P. N. Bibcode: 2001SoPh..203..211M Altcode: From a series of 1400 white-light images of solar granulation spanning a time period of 8.2 hours, skeletal plots of time-slice diagrams are derived showing intergranular lane positions as a function of time. The diagrams permit to automatically track, classify, and relate 42 186 granules. Recurrently fragmenting granules are found that survive by means of their descendants for more than 3 hours. Such long-lived active granules tend to have a mean spatial distance along the slice of about 10 Mm. This distance decreases with decreasing minimal required lifetime. Since active granules are expected to generate a steadily divergent flow over a long period of time, it is suggested to identify them as a source of the mesogranular flow. Deficiencies of the time-slice analysis are discussed. The relative frequency of different types of granules and the granule decay time as derived from the time-slice diagrams are compared with corresponding results of previous works. Title: Modeling VIRGO Spectral and Bolometric Irradiances with MDI Data Authors: Steinegger, M.; Hanslmeier, A.; Otruba, W.; Brandt, P. N.; Eker, Z.; Wehrli, C.; Finsterle, W. Bibcode: 2001ASSL..259..283S Altcode: 2001dysu.conf..283S The last solar activity minimum in 1996 was characterized by several periods without any sunspots or faculae visible on the solar disk. Between these extremely quiet intervals, from time to time a single active region emerged and developed. The passage of these individual active regions across the visible solar hemisphere was accompanied by a pronounced variation in the solar irradiance as observed by VIRGO onboard SOHO. Making use of photometric full-disk observations of the Sun obtained by MDI we try to reconstruct the temporal behaviour of the three spectral and the total irradiance channels measured by VIRGO by applying starspot modeling techniques. In this paper we mainly discuss possible error sources. Title: Computational Methods concerning the Solar Granulation Authors: Pötzi, W.; Hanslmeier, A.; Brandt, P. N. Bibcode: 2001ASSL..259..223P Altcode: 2001dysu.conf..223P In this paper an overview is given concerning the automatic detection of granules in long time series and the derivation of characteristic parameters. Title: Preliminary study of the evolution of solar magnetic structures and photospheric horizontal velocity fields Authors: UeNo, S.; Kitai, R.; Ichimoto, K.; Sakurai, T.; Soltau, D.; Brandt, P. N. Bibcode: 2001AdSpR..26.1793U Altcode: In October 1997, we made a coordinated observation of the solar photosphere and chromosphere at Hida observatory (Kyoto university, Japan) and at Teide observatory (Tenerife) over a 10 day. We obtained imaging data series continuously during 6 hr 45 min in G-band (4308 Å) observed with the Domeless Solar Telescope (DST) at Hida on 24th October (effective FOV; 96″×99″). Additionally, in this observation, we simultaneously observed image series of the chromosphere during the latter 4 hr 10 min in H α line center and H α ±0.6 Å. From these data set, we could detect that emerging flux tubes crossed the photosphere to the chromosphere and that 'convective collapse' phenomena appeared at the stage of the spot formation. Moreover, we confirmed that the lifetime of mesogranulation was about 4000 sec (70 min) from the temporal evolution of velocity patterns. We show here only a summary of these observations. Title: Coordinated MDI/TRACE/SVST Observations of Sunspots Authors: Bush, R. I.; Shine, R. A.; Brandt, P.; Sobotka, M.; Scharmer, G. Bibcode: 2000SPD....31.0122B Altcode: 2000BAAS...32R.804B During the first two weeks of June 1999, coordinated observations of sunspots were made by the MDI instrument on the SOHO spacecraft, the TRACE satellite and the Swedish Vacuum Solar Tower (SVST) at La Palma. The MDI instrument was operating in a "high resolution" mode and was obtaining 1.2 arc-second resolution magnetograms and 2.4 arc-second resolution dopplergrams at a one minute cadence. TRACE observations were made in Fe IX/X 171 Angstroms and/or Fe XII 195 Angstroms together with the 1600 Angstroms and continuum bands at a 1.0 arc-second resolution. The SVST data consist of filtergrams taken with three 2Kx2K CCD cameras with about 0.4 arc-second resolution operating in frame selection mode. The first camera used a fixed G band (4305 Angstroms) filter, the second a fixed blue continuum filter (4507 Angstroms), and the third a narrow band tunable filter which was cycled through several positions in the Hα line and the 6302 Angstroms Fe ~I line. The goal of this investigation is to detail the evolution of stable sunspots in order to understand the detailed correlation of photospheric flows and magnetic features. The high time and spatial resolution of these measurements provides a unique opportunity to explore the interactions of plasma and magnetic field at the solar surface. This work was supported by NASA grant NAG5-3077 at Stanford and NASA contract NAS5-38099 at Lockheed Martin. Title: Small-scale topology of solar atmosphere dynamics. IV. On the relation of photospheric oscillations to meso-scale flows Authors: Hoekzema, Nick M.; Brandt, Peter N. Bibcode: 2000A&A...353..389H Altcode: We use a high quality five-hour sequence of images of the solar photosphere taken at the Swedish Solar Vacuum Telescope, La Palma, to study the relation of meso-scale divergence with the amplitudes of photospheric intensity oscillations. Meso-scale flows are determined by local correlation tracking of the granulation. Statistical evaluation of the co-location probability of regions with more than twice the average oscillation amplitude and regions with high or low meso-scale divergence shows that high amplitude regions are preferentially located in regions of negative divergence (convergence) and avoid meso-divergent regions. Additionally we confirm the increase of granule brightness in regions of positive divergence with the opposite effect in regions of convergence. Title: Fine structure in sunspots. III. Penumbral grains Authors: Sobotka, M.; Brandt, P. N.; Simon, G. W. Bibcode: 1999A&A...348..621S Altcode: The properties of penumbral grains (PGs) in a medium-size sunspot are studied from a 4.5 hour observation series acquired on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma. The application of an image segmentation procedure and a feature tracking algorithm on a movie of 360 frames yields proper motions, intensities, and lifetimes for a set of 469 PGs. Almost 3/4 of the PGs move toward the umbra and more than 1/4 toward the photosphere. There appears to be a dividing line (DL) in the penumbra, approximately 0.7 of the distance from the umbra to the photosphere, such that most PGs outside this line move toward the photosphere, and those inside move toward the umbra. For inward moving PGs we find a typical proper motion speed of 0.4 km s(-1) and a median lifetime of 29 minutes, for outward moving ones 0.5 km s(-1) and 22 minutes. The average speed of inward moving PGs increases with distance from the umbra with a maximum near the DL. Outward moving PGs have maximum speed near the outer penumbral boundary. The measured instantaneous velocities of individual PGs show only partial agreement with theoretical model predictions. We find much shorter lifetimes than earlier authors, and no pronounced dependence of lifetime on position in the penumbra. We discuss possible reasons for the disagreement with previous results. Title: Shift-and-add reconstruction of solar granulation images Authors: Baba, N.; Miura, N.; Sakurai, T.; Ichimoto, K.; Soltau, D.; Brandt, P. Bibcode: 1999SoPh..188...41B Altcode: To restore an atmospherically degraded image of solar granulation the shift-and-add (SAA) method is applied to its specklegrams. It is the first time, to the best of our knowledge, that such a technique has been used for image reconstruction of solar granulation, a largely extended target. SAA, therefore, enables us to monitor restored images of solar granulation in a simple and fast way. Title: Resolution Improvement of Solar Images Authors: Miura, Noriaki; Baba, Naoshi; Sakurai, Takashi; Ichimoto, Kiyoshi; Soltau, Dirk; Brandt, Peter Bibcode: 1999SoPh..187..347M Altcode: A method for the improvement of resolution in an observed solar image is proposed. A blind deconvolution method is used for restoration of an atmospherically-degraded solar image, and a super-resolution method is applied to its restored image to improve the resolution. It is confirmed that a blind deconvolution process can restore fine structures that are blurred in an observed image, and that the super-resolution process can make a cutoff frequency in a blind-deconvolved image higher. A time series of super-resolved images of a sunspot observed with the 70-cm Vacuum Tower Telescope at Teide Observatory is presented. Title: Modelling of Solar Irradiance Variations Authors: Otruba, W.; Brandt, P. N.; Eker, Z.; Hanslmeier, A.; Steinegger, M. Bibcode: 1999ASSL..239..213O Altcode: 1999msa..proc..213O A modelling of the sunspot deficit in solar irradiance measurements in 3 spectral wavelengths and the total flux as observed by the VIRGO experiment on SOHO has been performed for several periods of 1996 in a pixel-by-pixel manner using high resolution photoheliograms taken at Kanzelhöhe Observatory. The calculation of the irradiance contributions of the other features of active regions is in progress. Title: Some Properties of the Solar Granulation and Mesogranulation Authors: Mühlmann, W.; Hanslmeier, A.; Brandt, P. N. Bibcode: 1999ASSL..239..223M Altcode: 1999msa..proc..223M Based on a 8.7 hour time series of solar granulation images (Simon et al., 1994), of a spatial resolution mostly better than 400 km, we calculated some properties of granules, vorticity and divergence of the velocity fields and we tried to determine the mesogranular pattern by corks. Title: Small-scale topology of solar atmosphere dynamics. III. Granular persistence and photospheric wave amplitudes Authors: Hoekzema, N. M.; Brandt, P. N.; Rutten, R. J. Bibcode: 1998A&A...333..322H Altcode: 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 long-lived ``intergranular holes'' discovered by \cite*{Roudier+others1997} %T AA: intergranular plumes + BP formation and the 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 holes. There is large persistency difference between the brightest and the darkest features; some of the latter have location memories as long as two hours. In addition, the darkest intergranular features are found to be sites of enhanced Fourier modulation in the 3-min acoustic regime, improving earlier results through much higher statistical significance. However, the persistency regions containing intergranular holes do not seem to produce the excess acoustic emission that would be expected above downflow plumes. Title: On the Determination of the Quiet-Sun Center-to-Limb Variation in CA II K Spectroheliograms Authors: Brandt, Peter N.; Steinegger, Michael Bibcode: 1998SoPh..177..287B Altcode: We present a method for the determination of the center-to-limb variation (CLV) for Caii K spectroheliograms. It is based on the calculation of intensity histograms for rings of constant area. Using a simple cutoff criterion in the cumulative histograms, we are able to derive CLVs of the quiet Sun regardless of the solar activity level. Using an example from the literature, we show in which way different methods of normalization of the quiet-Sun CLV may affect the results. Title: Small-scale topology of solar atmosphere dynamics. I. Wave sources and wave diffraction Authors: Hoekzema, N. M.; Rutten, R. J.; Brandt, P. N.; Shine, R. A. Bibcode: 1998A&A...329..276H Altcode: We study the small-scale topology of dynamical phenomena in the quiet-sun internetwork 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 we concentrate on the topology of short-duration Fourier amplitude maps for the photosphere and the simultaneously observed overlying chromosphere. We find that these maps portray a complex mix of global modes and locally excited waves which necessitates a statistical approach. Various aspects including mesoscale patterning indicate the presence of subsurface wave sources and of subsurface wave diffraction by convective inhomogeneities. Title: Fine structure in sunspots. I. Sizes and lifetimes of umbral dots Authors: Sobotka, Michal; Brandt, Peter N.; Simon, George W. Bibcode: 1997A&A...328..682S Altcode: The analysis of a 4 1/2 hour series of high resolution white light observations of the umbra in a medium-size sunspot (NOAA 7519, observed on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma) is described. An automatic identification and tracking algorithm was applied to umbral dots (UDs) observed in a destretched movie of 360 frames. In total, 662 UDs were tracked and their filling factor, sizes, and lifetimes were measured. It was found that large (diameter > 0farcs 4) and long-lived (lifetime > 10 minutes) UDs appear mostly in regions with enhanced umbral diffuse background intensity. UDs do not have a ``typical'' size. Their number rapidly increases with decreasing diameter down to the resolution limit. Similarly, UDs do not have a ``typical'' lifetime, and their number rapidly increases with decreasing lifetime. UDs with lifetimes below 10 minutes represent about 2/3 of the population; the median lifetime is 5.9 minutes. Title: Fine structure in sunspots. II. Intensity variations and proper motions of umbral dots Authors: Sobotka, Michal; Brandt, Peter N.; Simon, George W. Bibcode: 1997A&A...328..689S Altcode: Temporal intensity variations of umbral dots (UDs) and dark nuclei (DNs), and proper motions of UDs, were analyzed in a 4 1/2 hour time series of high resolution white light images of the umbra in a medium-size sunspot (NOAA 7519). The observations were made on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma. An identification and tracking algorithm was applied to UDs observed in a destretched movie of 360 frames. In total, 662 UDs were tracked, and their intensities, positions, and proper motions were measured. Power spectra of temporal intensity variations of UDs and DNs were computed, and several typical periods were found. The histogram of time-averaged intensities of UDs has two maxima; the UDs belonging to the brighter part of the population are located mostly at or near the umbral-penumbral boundary. The number of UDs decreases with increasing magnitude of the proper motion velocity. Speeds of UDs are grouped at 100 and 400 m/s. The observed spatial distribution of UDs with different proper motion velocities is found to be in contradiction to the generally accepted idea of moving ``peripheral'' and stationary ``central'' UDs. Both ``fast'' and ``slow'' UDs are present in all parts of the umbra. Thus velocity does not appear to be a good criterion for separating UDs into ``peripheral'' and ``central'' ones. Title: On Novel Methods to Determine Areas of Sunspots from Photoheliograms Authors: Pettauer, T.; Brandt, P. N. Bibcode: 1997SoPh..175..197P Altcode: Two novel methods of measuring umbral and penumbral areas of sunspots and of complex sunspot groups are described. Both methods comprise the digitization of photoheliograms by a frame grabber and the computation of intensity histograms of selected areas of activity. The first method, called `cumulative histogram method', in principle determines the intensity boundaries umbra-penumbra and penumbra-photosphere from the intersections of linear fits into the corresponding parts of the cumulative histograms of sunspots. The second method, called `maximum gradient method', marks image pixels of a given intensity level ±2 units wide as a white isophote on a display. Interactive variation of this level makes it easy to visually select the contour line fitting the boundary penumbra-photosphere (or umbra-penumbra) best. At the same level usually the width of the contour line is smallest. In both cases the summation of the pixel numbers above the corresponding intensity levels yields the umbral and the total sunspot areas, respectively. Some limitations of the two methods are discussed. Title: Modelling Solar Irradiance Variations with an Area Dependent Photometric Sunspot Index Authors: Brandt, P. N.; Stix, M.; Weinhardt, H. Bibcode: 1994SoPh..152..119B Altcode: 1994IAUCo.143..119B; 1994svs..coll..119B The He 1083 nm line equivalent width and the 10.7 cm radio flux are employed to model the total solar irradiance corrected for sunspot deficit. A new "area dependent photometric sunspot index" (APSI) based on sunspot photometry by Steinegger et al. (1990) is used to correct the irradiance data for sunspot deficits. Two periods of time are investigated: firstly, the 1980-1989 period between the maxima of solar cycles 21 and 22; this period is covered by ACRIM I irradiance data. Secondly, the 1978-92 period which includes both maxima; here, the revised Nimbus-7 ERB data are used. Title: Changes of the Fe I spectral line parameters as a functin of the magnetic flux (solar disk centre). Authors: Brandt, P. N.; Gadun, A. S. Bibcode: 1993KFNT....9....8B Altcode: 1993KNFT....9....8B The parameter variations of the 281 Fe I lines (asymmetry, depth, equivalent width, halfwidth) are analysed in three regions near the solar disk centre, having different magnetic fluxes. The analysis shows that the line parameter variations depend on the line strength, the lower excitation potential and the line sensitivity to the magnetic field. A qualitative interpretation of the results is given. Title: Variation of granulation properties on a mesogranular scale Authors: Brandt, P. N.; Ferguson, S.; Shine, R. A.; Tarbell, T. D.; Scharmer, G. B. Bibcode: 1991A&A...241..219B Altcode: A 79 min series of CCD images of the solar granulation with subarcsec spatial resolution is analyzed. Local correlation techniques are applied to determine horizontal displacements of the granular intensity pattern in a 14.2 by 12.2 sq arcsec field of view. The divergence of the average horizontal flow field shows mean cell sizes of 5 to 7 arcsec. Granules are selected with respect to area, brightness, lifetime, and expansion rate. It is shown that small, faint, short-lived, and fast collapsing granules are located preferentially in the negative divergence (down-draft) regions of the mesogranular flow field, while bright, long-lived, and rapidly expanding granules populate preferentially the positive divergence (up-draft) regions. The differences in area coverage range between + or - 6 percent and + or - 9 percent. Title: On the Umbra / Penumbra Area Ratio of Sunspots Authors: Brandt, P. N.; Schmidt, W.; Steinegger, M. Bibcode: 1990SoPh..129..191B Altcode: The area ratio of umbra to penumbra (Au/Ap) was investigated for a series of 126 sunspots observed around the maximum of solar activity in 1980. Plotting log (Au) as function of log (Ap) a linear relation is obtained with a slope of 1.10, yielding an average ratio Au/Ap of 0.24 for small spots and of 0.32 for large spots. This deviates noticeably from the commonly adopted constant value of Au/Ap = 0.21 (Allen, 1973) used e.g. for modelling the sunspot irradiance deficit (cf. Willson et al., 1981) from the Solar Geophysical Data. Title: Sunspot Photometry and the Total Solar Irradiance Deficit Measured in 1980 BY ACRIM Authors: Steinegger, M.; Brandt, P. N.; Pap, J.; Schmidt, W. Bibcode: 1990Ap&SS.170..127S Altcode: Until now a simple Photometric Sunspot Index (PSI) model was used (e.g. Willsonet al., 1981) to describe the contribution of sunspots to the solar irradiance deficit measurement by ACRIM. In this work we replace this model by a photometry of sunspot pictures for the period of 19 August to 4 September, 1980 taking into account the individual features, like lightbridges or umbral dots, of each spot. The main results of this preliminary analysis are: (1) theA u/A p ratios and alsos the α values vary in a wide range and are by no means constant as in the PSI model; (2) the general trend of the irradiance deficit from our analysis agrees well with the ACRIM measurements; (3) on some days there are differences of more than 50% between the deficits derived from our measurements and from the PSI model. Title: Solar line asymmetries and the magnetic filling factor Authors: Brandt, P. N.; Solanki, S. K. Bibcode: 1990A&A...231..221B Altcode: Results are presented of an analysis of high-quality Fourier transform spectrometer spectra obtained in facular regions near solar disk center having different amounts of magnetic flux or, equivalently, different filling factors, alpha. The line parameters (width, equivalent width, depth, bisector shape, and wavelength) of 32 spectral lines and their variation with alpha are studied. Line depth is seen to decrease with increasing filling factor for all the observed lines, while the line width increases, even after compensation has been made for the Zeeman broadening. For strong or temperature-insensitive lines the equivalent width stays practically unchanged, but decreases for weak lines. The findings are qualitatively explained by a decrease in the contrast between the upflow and downflow components of the nonmagnetic part of the atmosphere in active regions (abnormal granulation) coupled to either a decrease in the average temperature of the nonmagnetic part or a significant increase in small-scale velocity. Title: Horizontale Eigenbewegungen der solaren Granulation: Mesogranulation und Wirbelstruktur. Authors: Brandt, Peter N. Bibcode: 1990S&W....29..164B Altcode: The main problems related to solar observations are reviewed, and recent advances in the technology of observation and analysis are reviewed. Recent findings on the convection dependency of the motion of solar granules are discussed. These convective cells are 5000-6000 km in breadth and are called mesogranulation. They are intermediate in size between those resulting from granulation and from supergranulation. The observation of an eddy in the mesogranulation is reported. Title: On the fractal dimension of the solar granulation Authors: Greimel, R.; Brandt, P. N.; Guenther, E.; Mattig, W. Bibcode: 1990VA.....33..413G Altcode: Fractal dimension analysis may be used to determine whether the solar granulation represents homogeneous, isotropic turbulence in certain ranges of scale. Several attempts have been made to investigate this fractal dimension from white light granulation pictures of high spatial resolution, e.g. Roudier and Muller (1986), Darvann and Kusoffsky (1989), and Karpinsky (1990), who find a critical scale of granule sizes, at which the fractal dimension d changes abruptly. Using material from the "Spektro-Stratoskop" and analysing 42 742 granules, we could confirm the results published earlier, i.e. a fractal dimension of approx. 1.3 for the small scales and d ≈ 2 for the large scales. However, we find a smooth transition between both regimes. Moreover, a closer inspection of the methods used reveals, that in all analyses the fractal dimension of the granulation at small scales seems to be dominated by technical problems, i.e. the limited resolution of the material, the definition of the granules, and — last but not least — the finite pixel size. Title: Vortex flow in the solar photosphere Authors: Brandt, P. N.; Scharmer, G. B.; Ferguson, S.; Shine, R. A.; Tarbell, T. D.; Title, A. M. Bibcode: 1988Natur.335..238B Altcode: Convective flow fields in the solar atmosphere play a key role in the concentration and dispersal of magnetic flux1, but because the individual flow elements-the solar granules-are a few arcsec or less in size, studies of their motions have been limited by the distortion and blurring of the Earth's atmosphere ('seeing'). We report here a very high-quality series of granulation images taken at the new Swedish Solar Observatory on La Palma (Canary Islands) which have permitted flow measurements at the sub-arcsec level. These movies show a vortex structure which visibly dominates the motion of the granules in its neighbourhood and persists for the 1.5 h duration of the movie. If such vortices are a common feature of the solar convective zone, they may provide an important mechanism for the heating of stellar chromospheres and coronae by twisting the footprints of magnetic flux tubes. Title: Day-time seeing statistics at Sacramento Peak Observatory Authors: Brandt, P. N.; Mauter, H. A.; Smartt, R. Bibcode: 1987A&A...188..163B Altcode: A method for the photoelectric measurement of angle-of-arrival fluctuations at the solar limb is described, from which Fried's seeing parameter r0 can be determined. From a set of 2092 measurements, each of 10 s duration, performed on 146 observing days in the period from June 84 to September 86 at the solar vacuum tower telescope of the Sacramento Peak Observatory, a log-normal distribution of the r0 values gave a median r0 = 8.7 cm (measured at λ = 510 nm), with a standard deviation σ = 0.25 in logarithmic units. The results are compared with atmospheric sounding experiment data and longterm day- and night-time seeing statistics obtained at other observatories. Title: Ändert sich die Struktur der Granulation mit dem solaren Aktivitätszyklus? Authors: Brandt, P. N. Bibcode: 1986S&W....25..128B Altcode: It is pointed out that the 11-year solar activity cycle is of basic importance for a number of phenomena on the sun itself, in interplanetary space, and on earth. A number of decades ago, the possibility was considered that changes in the structure of granulation are a function of the solar activity cycle. The observational techniques existing at that time could not provide an unequivocal answer to this question. In the last few years, the number of observations which indicate cyclic chanages in the structure of granulation has increased. The characteristics of granulation are discussed, taking into account the flow and velocity of matter, changes regarding the size and appearance of the granules on the sun, the magnetic fields on the sun, and differences between characteristics in active and quiet areas. Attention is also given to new information obtained with the aid of an observational method which is based on an analysis of the light integrated over the entire visible solar disk. Title: The JOSO site testing campaigns in the Canary Islands Authors: Brandt, P. N.; Righini, A. Bibcode: 1985VA.....28..437B Altcode: In 1968 an informal cooperation of European solar research institutions was established under the name of JOSO (Joint Organization for Solar Observations). A brief account is given of the site testing carried out by this organization to find an "ideal" solar observatory site. After having tested nearly 40 sites in the Mediterranean and Atlantic coastal areas, it was found that, notwithstanding the great homogeneity of the maritime airmasses, coastal sites were not suitable for high resolution solar observations. Consequently, in the search for mountain sites imbedded in highly homogeneous air, two sites were chosen in the Canary Islands: Izaña (Tenerife) and Roque de los Muchachos (La Palma). Aircraft and radiosonde tests of the microthermal vertical profile in the atmosphere have shown the superior homogeneity of the Atlantic airmass above the Canary Islands. An extended test of 160 days (in 1979) of meteorological and solar observations performed simultaneously with two telescopes, both photographically and with photoelectric seeing monitors, has led to the conclusion that the Izaña site is somewhat superior to the site at Roque de los Muchachos as far as daytime seeing is concerned. Measurements during and after the campaign have also shown that for certain periods during daytime the telescopes installed at both sites appear to be inside the large-scale airmass whose residual inhomogeneities limit the night-time seeing. Title: On the centre-to-limb variation and latitude dependence of the asymmetry and wavelength shift of the solar line λ 5576 Authors: Brandt, P. N.; Schroeter, E. H. Bibcode: 1982SoPh...79....3B Altcode: Low noise photoelectric measurements of the line profile of the g = 0 Fe line gl 5576.097 combined with determinations of the wavelength shift of its centre calibrated by use of an I2 absorption tube are reported. Measurements taken at various limb distances (1.0 ≤ cos ϑ ≤ 0.2) and along 4 different diameters of the Sun are used to investigate the behaviour of the line asymmetry (C-shape) and wavelength shift of the line centre as functions of cos ϑ and of latitude and to search for possible pole-equator differences. Title: Solar site-testing campaign of JOSO on the Canary Islands in 1979 Authors: Brandt, P. N.; Woehl, H. Bibcode: 1982A&A...109...77B Altcode: Results of the campaign of testing undertaken by the European JOSO (Joint Organization for Solar Observations) in order to find an excellent site for solar observations are presented. Measurements with telescopes of 40 and 45 cm aperture and photoelectric seeing measurements were made at the sites of Izana and Roche de los Muchachos on the Canary Islands of Tenerife and La Palma, respectively. Observations obtained on 160 days between April and November, 1979 demonstrate the superiority of Izana in the area of image sharpness, although both sites offer an increase of one order of magnitude in the duration of good seeing compared to existing European stations. Photographs of the solar granulation taken from July to November confirm the superiority of Izana, where 4.5% of the exposures exhibit very high quality compared to 1.4% at Roche de los Muchachos. Analysis of meteorological records indicates that Izana is capable of providing 3000 hour/year of usable solar observations, and suggest an explanation for the higher quality of the Izana site. Title: Solar pulsations and angular coherence of atmospheric transparency fluctuations. Authors: Grec, G.; Brandt, P.; Fossat, E.; Duebner, F. L. Bibcode: 1979A&A....77..347G Altcode: It is noted that radial-velocity measurements in integrated sunlight are contaminated by atmospheric noise due to inhomogeneous transparency of earth's atmosphere along the line of sight to the solar disk. A measurement of the angular autocorrelation function of slow fluctuations in atmospheric transparency is described. It is shown that the typical coherence size is about 1 deg and independent of fluctuation amplitudes of 0.7 percent to 30 percent and that the angular autocorrelation function provides a link between global transparency variations and spurious measured velocities. It is concluded that all ground-based full-disk Doppler measurements should be carefully interpreted because atmospheric noise is present for periods greater than 5 min and less than about 90 min. Title: Tests of 4 Single-Stage Image Intensifier Tubes for Solar Spectroscopy Authors: Brandt, P. N.; Wiesmeier, A. Bibcode: 1974SoPh...38..517B Altcode: Atmospheric image degradation can be reduced by shortening the exposure time. Therefore, four single-stage electrostatically focused image intensifier tubes with fiber optic output were tested in the laboratory for their suitability in solar spectroscopy. Under the premise that the spatial and spectral image scales (Capri: 5.9″ mm−1 and 9 mm Å−1, resp.) should not be changed by a premagnification, the RCA tube 8605/V1 in combination with Copex Pan Rapid film turns out as the best choice. It yields a resolution of 55 line-pairs mm−1 and a gain of exposure time by a factor of ≈ 14 over Kodak IV-E in the red, with only little increase of photometric noise but appreciable pin-cushion distortion. Title: On the Determination of Noise in Photographic Measurements of Solar Velocities and Magnetic Fields Authors: Brandt, P. N.; Nesis, A. Bibcode: 1973SoPh...31...75B Altcode: The noise in photographic measurements of solar velocities and magnetic fields is assumed to be essentially determined by the granularity of the film, its gamma, the scanning spot size and the parameters of the specific spectral line. A formula is derived which serves for a quantitative estimate of the rms velocity and magnetic field noise when evaluating spectrograms and spectroheliograms. Four typical examples are treated and show that the estimate is correct within 20%. Title: Measurement of Solar Image Motion and Blurring Authors: Brandt, P. N. Bibcode: 1970SoPh...13..243B Altcode: An investigation being carried out at the Fraunhofer Institut is described; it has two aims: to establish a simple method for the quantitative measurement of solar seeing effects and to obtain informations of their dependence on telescopic aperture. Title: Frequency Spectra of Solar Image Motion Authors: Brandt, P. N. Bibcode: 1969SoPh....7..187B Altcode: The frequency analysis of image motion (IM) at the solar limb was carried out in the frequency range from 0.5 to 50 Hz using a photoelectric equipment. For a telescopic aperture of 35 cm and a bandwidth of 0.65 Hz a typical frequency spectrum under average observing conditions shows a decrease of amplitude from 2 arcsec at 0.5 Hz to 0.4 arcsec at 5 Hz, 0.03 arsec at 50 Hz (and < 0.01 arcsec at 500 Hz). Visually estimated values of image steadiness seem to be in better agreement with the r.m.s. value of image motion (scattering parameter σ) than with the amplitude at a certain frequency (Figures 5a, b). The influence of IM on the quality of photographic pictures or on spectra of solar fine structures is calculated as a function of exposure time. Table II gives the IM scattering parameters σ (0.01 arcsec to 4 arcsec) calculated for exposure times from 0.001 to 0.5 sec — valid for a time average. The modulation transfer functions (MTF, one-dimensional) derived from the IM scattering parameters are presented in Figure 7 together with the MTF for a diffraction-limited telescope of 35 cm aperture at λ 6000 Å. Exposure times of less than approximately 0.01 sec (certain within a factor of 2) render the influence of IM negligible compared to the MTF of the objective used for this investigation. Title: Modulation Transfer Functions of some Solar Recording Films Authors: Brandt, P. N. Bibcode: 1967SoPh....2..211B Altcode: The modulation-transfer functions (MTF) of four solar recording films (Eastman-Kodak: 103a-G, IV E, RAR-SO-375; Gevaert: Duplopan-Rapid) are measured with the aid of an interference device. The MTF is used to estimate the smallest detectable element of a two-dimensional pattern; the so-called `detectability threshold' a* depends on: intensity modulation m, square of MTF, required signal-to-noise ratio q, gamma and granularity of the film. The calculated values of a* for the four emulsions are given in Table II. Finally the influence of exposure time on image quality is discussed.