Small-scale structure and dynamics of the lower solar atmosphere

The chromosphere of the quiet Sun is a highly intermittent and dynamic phenomenon. Three-dimensional radiation (magneto-)hydrodynamic simulations exhibit a mesh-like pattern of hot shock fronts and cool expanding post-shock regions in the sub-canopy part of the inter-network. This domain might be called "fluctosphere". The pattern is produced by propagating shock waves, which are excited at the top of the convection zone and in the photospheric overshoot layer. New high-resolution observations reveal a ubiquitous small-scale pattern of bright structures and dark regions in-between. Although it qualitatively resembles the picture seen in models, more observations - e.g. with the future ALMA - are needed for thorough comparisons with present and future models. Quantitative comparisons demand for synthetic intensity maps and spectra for the three-dimensional (magneto-)hydrodynamic simulations. The necessary radiative transfer calculations, which have to take into account deviations from local thermodynamic equilibrium, are computationally very involved so that no reliable results have been produced so far. Until this task becomes feasible, we have to rely on careful qualitative comparisons of simulations and observations. Here we discuss what effects have to be considered for such a comparison. Nevertheless we are now on the verge of assembling a comprehensive picture of the solar chromosphere in inter-network regions as dynamic interplay of shock waves and structuring and guiding magnetic fields.Comment: 8 pages, 2 figures, to appear in the proceedings of the IAU Symposium No. 247, Waves & Oscillations in the Solar Atmosphere: Heating and Magneto-Seismology (Venezuela 2007

High-resolution observations of the solar photosphere and chromosphere

Observations of the sun are almost always impaired by the turbulent motion of air in Earth's atmosphere. The turbulence would limit the theoretical resolution of modern large telescopes to that of amateur telescopes without additional tools.Today however, high-resolution data of the Sun are necessary to invesitgate its small-scale structure. This structure is likely to be connected to the radially outward increasing temparature distribution of the solar atmosphere. An introduction into further details of this topic that has also been the motivation for this work is presented in Chapt. 1. A theory of atmospheric turbulence that builds the basis for several results of this work is described in Chapt. 2. Here, two modern tools to enhance the resolution of groundbased observations are reviewed, on the one hand adaptive optics (AO) systems and on the other hand speckle interferometry. Until recently, these two techniques were only used separately. In Chapt. 3 the necessary modifications for analytical models of transfer functions are developed that include the changes made by an AO system to the incoming wave front, thus making a combination of AO systems and speckle interferometry possible ...thesi

Migration und Entwicklung

Mexiko ist der weltweit drittgrößte Empfänger von monetären Remittances. Die Rücküberweisungen mexikanischer MigrantInnen sind eine wichtige Einnahmequelle vieler mexikanischer Haushalte und haben entscheidenden Einfluss auf die lokale, regionale und nationale Entwicklung. Die meisten wissenschaftlichen Studien, die bisher über Rücküberweisungen nach Mexiko publiziert wurden, konzentrierten sich auf ländliche Regionen. Urbanen Haushalten wurde bisher wenig Aufmerksamkeit zuteil, obwohl in den letzten Jahrzehnten, infolge der Urbanisierung der mexikanischen Gesellschaft, der Anteil an AuswandererInnen mit urbanen Herkunftsregionen und folglich auch von Rücküberweisungen in mexikanische Städte gestiegen ist. Die vorliegende Arbeit befasst sich mit der Rolle von individuellen monetären Remittances in den urbanen Haushalten Mexiko Citys. Basierend auf 140 Interviews mit Haushaltsvorständen der Gemeinde Chimalhuacán, die innerhalb der Metropolregion des Tals von Mexiko liegt, wird erörtert, welchen Stellenwert Rücküberweisungen für die urbanen Haushalte haben und wie sich die sozio-ökonomischen Verhältnisse der Remittances-empfangenden Haushalte von allen anderen Haushalten unterscheiden.Mexico is the world's third-largest recipient of monetary remittances. The money transferred by Mexican emigrants to their home country is an important source of income for many Mexican households and has a significant impact on the local, regional and national development. The existing body of research on remittance flows to Mexico has concentrated mainly on rural communities. Although, as a result of the urbanisation of Mexican society, the share of urban-origin Mexican emigrants and consequently of remittance flows to urban areas has increased, relatively little is known about remittance flows to urban households. Therefore, this study explores the role of individual monetary remittances in urban households in Mexico City. Based on interviews with 140 head of households in Chimalhuacán, a municipality located in the Mexico City Metropolitan Area, the study analyses the significance of remittances for urban households and the socio-economic differences between remittance recipient and non-recipient households

A Revision of the Murinae (Rodentia, Mammalia) of Kohfidisch (Upper-Miocene, Burgenland, Austria)

Die Obermiozäne Fossilfundstelle Kohfidisch, die sich im Süden des Burgenlandes (Österreich) befindet wurde Mitte der 50ger Jahre entdeckt. Ab diesem Zeitpunkt wurde das Höhlen- und Spaltensystem bis in die Mitte der 80ger für mehr als 30 Jahre im Zuge jährlicher Geländearbeiten, von zwei der großen Paläontologen ihrer Zeit, Friedrich Bachmayer und Helmuth Zapfe, begraben. Die Fundstelle lieferte eine Vielzahl an verschiedenen Vertebraten- und Invertebratentaxa. Unter den häufigsten Formen waren die Murinae deren Fossilien sich auf geschätzte 1800 Mandibel- und Maxilarfragmente sowie 5500Einzelzähne, jedoch lediglich auf wenige postcraniale Fragmente belaufen. Sie sind von Kohfidisch mit zwei Arten dokumentiert, nämlich Apodemus lugdunensis und Progonomys woelferi – für letztere ist Kohfidisch die dokumentierte Typuslokalität. Die intensive Erforschung dieser Gruppe von Kleinsäugern, speziell in Südwesteuropa, in den vergangen Jahrzehnten führten nicht nur zu einer Vielzahl neu beschriebener Taxa, sondern konnte auch ihre Relevanz für die terrestrische Biostratigraphie verdeutlichen. Die neuen Entwicklungen in der Erforschung der Murinae ließen eine Revision des Materials von Kohfidisch an der Zeit erscheinen, ganz besonders da früheren Studien nur ein kleiner Teil des gesamten Materials zu Grunde lag. Ziel der vorliegenden Arbeit war es dieses Material zu überarbeiten und eine genauere Erfassung der Variationsbreite der beiden vorkommenden Arten zu erzielen sowie detailliertere Beschreibungen und mehr Bilder mit höherer Auflösung mittels Elektronenmikroskopie zu liefern. Durch die Revision konnte das Auftreten einer dritten bisher aus Kohfidisch nicht bekannten Art, Progonomys cf. hispanicus nachgewiesen werden. Kohfidisch bekannt ist bisher die einzige Fundstelle in Österreich aus der diese Spezies dokumentiert werden konnte. Ein weiteres Ziel der vorliegenden Studie war es, das Material der einzelnen Fundpunkte bezüglich potenzieller Unterschiede zu untersuchen. Eine morphologische Merkmalsanalyse in Kombination mit multivariaten statistischen Methoden zeigte Unregelmäßigkeiten, die aber keine Muster erkennen ließen, welche endgültige Schlüsse über z. B. eventuelle Altersunterschiede der einzelnen Spalten zugelassen hätten.The Upper Miocene fossil locality of Kohfidisch, situated in the south of Burgenland (Austria) was discovered in the mid 1950’s. From this time onwards the cave and fissure system has been depleted in annual excavations for almost 30 years until the mid 1980’s by two of the great palaeontologists of that time, Friedrich Bachmayer and Helmuth Zapfe. The fossil site yielded a multitude of different vertebrate and invertebrate taxa. Among the most abundant forms were the murines, which yielded an estimated number of 1800 mandibular and maxillary fragments and about 5500 single teeth, but only few postcranial remains. Murines are known from Kohfidisch with two species, namely Apodemus lugdunensis and Progonomys woelferi, for the latter of which Kohfidisch is the documented type locality. The intensive study of this group of small mammals especially in south-western Europe in the past decades did not only lead to the description of many new taxa, but also revealed their importance for terrestrial biostratigraphy. These new developments in the study of murines, made a revision of the murine fossils of Kohfidisch due, especially since prior examinations dealt only with small portions of the material. The following study is aimed at achieving better estimations of the true range of variation of the occurring species including more detailed descriptions and more pictures at a higher resolution using electron microscopy. The revision of the murines revealed the occurrence of a third species Progonomys cf. hispanicus in addition to the two already established ones. Progonomys cf. hispanicus has not been documented for the site of Kohfidisch prior to this study and it is so far the only locality in Austria yielding this species. Another objective was to examine the material from the different finding points within the cave system with regards to potential differences. A morphological analysis of character states in combination with multivariate statistical methods showed some irregularities that however did not reveal any patterns, which might have allowed drawing any final conclusions about possible age differences of the separate fissures within the cave system

Observation of a short-lived pattern in the solar chromosphere

In this work we investigate the dynamic behavior of inter-network regions of the solar chromosphere. We observed the chromosphere of the quiet Sun using a narrow-band Lyot filter centered at the Ca II K 2v emission peak with a bandpass of 0.3A. We achieved a spatial resolution of on average 0.7" at a cadence of 10s. In the inter-network we find a mesh-like pattern that features bright grains at the vertices. The pattern has a typical spatial scale of 1.95" and a mean evolution time scale of 53s with a standard deviation of 10s. A comparison of our results with a recent three-dimensional radiation hydrodynamical model implies that the observed pattern is of chromospheric origin. The measured time scales are not compatible with those of reversed granulation in the photosphere although the appearance is similar. A direct comparison between network and inter-network structure shows that their typical time scales differ by at least a factor of two. The existence of a rapidly evolving small-scale pattern in the inter-network regions supports the picture of the lower chromosphere as a highly dynamical and intermittent phenomenon.Comment: Letter A&A 4 pages 5 figure

Inter-network regions of the Sun at millimetre wavelengths

The continuum intensity at wavelengths around 1 mm provides an excellent way to probe the solar chromosphere. Future high-resolution millimetre arrays, such as the Atacama Large Millimeter Array (ALMA), will thus produce valuable input for the ongoing controversy on the thermal structure and the dynamics of this layer. Synthetic brightness temperature maps are calculated on basis of three-dimensional radiation (magneto-)hydrodynamic (MHD) simulations. While the millimetre continuum at 0.3mm originates mainly from the upper photosphere, the longer wavelengths considered here map the low and middle chromosphere. The effective formation height increases generally with wavelength and also from disk-centre towards the solar limb. The average intensity contribution functions are usually rather broad and in some cases they are even double-peaked as there are contributions from hot shock waves and cool post-shock regions in the model chromosphere. Taking into account the deviations from ionisation equilibrium for hydrogen gives a less strong variation of the electron density and with it of the optical depth. The result is a narrower formation height range. The average brightness temperature increases with wavelength and towards the limb. The relative contrast depends on wavelength in the same way as the average intensity but decreases towards the limb. The dependence of the brightness temperature distribution on wavelength and disk-position can be explained with the differences in formation height and the variation of temperature fluctuations with height in the model atmospheres.Comment: 15 pages, 10 figures, accepted for publication in A&A (15.05.07

Morphology and Dynamics of the Low Solar Chromosphere

The Interferometric Bidimensional Spectrometer (IBIS) installed at the Dunn Solar Telescope of the NSO/SP is used to investigate the morphology and dynamics of the lower chromosphere and the virtually non-magnetic fluctosphere below. The study addresses in particular the structure of magnetic elements that extend into these layers. We choose different quiet Sun regions in and outside coronal holes. In inter-network regions with no significant magnetic flux contributions above the detection limit of IBIS, we find intensity structures with the characteristics of a shock wave pattern. The magnetic flux elements in the network are long lived and seem to resemble the spatially extended counterparts to the underlying photospheric magnetic elements. We suggest a modification to common methods to derive the line-of-sight magnetic field strength and explain some of the difficulties in deriving the magnetic field vector from observations of the fluctosphere.Comment: accepted by ApJ, 16 pages, 8 figure

The solar chromosphere at high resolution with IBIS. I. New insights from the Ca II 854.2 nm line

(Abridged) Aims: In this paper, we seek to establish the suitability of imaging spectroscopy performed in the Ca II 854.2 nm line as a means to investigate the solar chromosphere at high resolution. Methods: We utilize monochromatic images obtained with the Interferometric BIdimensional Spectrometer (IBIS) at multiple wavelengths within the Ca II 854.2 nm line and over several quiet areas. We analyze both the morphological properties derived from narrow-band monochromatic images and the average spectral properties of distinct solar features such as network points, internetwork areas and fibrils. Results: The spectral properties derived over quiet-Sun targets are in full agreement with earlier results obtained with fixed-slit spectrographic observations, highlighting the reliability of the spectral information obtained with IBIS. Furthermore, the very narrowband IBIS imaging reveals with much clarity the dual nature of the Ca II 854.2 nm line: its outer wings gradually sample the solar photosphere, while the core is a purely chromospheric indicator. The latter displays a wealth of fine structures including bright points, akin to the Ca II H2V and K2V grains, as well as fibrils originating from even the smallest magnetic elements. The fibrils occupy a large fraction of the observed field of view even in the quiet regions, and clearly outline atmospheric volumes with different dynamical properties, strongly dependent on the local magnetic topology. This highlights the fact that 1-D models stratified along the vertical direction can provide only a very limited representation of the actual chromospheric physics.Comment: 13 pages, 8 figures. Accepted in A&A. Revised version after referee's comments. New Fig. 1 and 7. Higher quality figures in http://www.arcetri.astro.it/~gcauzzi/papers/ibis.caii.pd

Basal Chromospheric Flux and Maunder Minimum-type Stars: The quiet-Sun Chromosphere as a Universal Phenomenon

Aims: We demonstrate the universal character of the quiet-Sun chromosphere among inactive stars (solar-type and giants). By assessing the main physical processes, we shed new light on some common observational phenomena. Methods: We discuss measurements of the solar Mt. Wilson S-index, obtained by the Hamburg Robotic Telescope around the extreme minimum year 2009, and compare the established chromospheric basal Ca II K line flux to the Mt. Wilson S-index data of inactive ("flat activity") stars, including giants. Results: During the unusually deep and extended activity minimum of 2009, the Sun reached S-index values considerably lower than in any of its previously observed minima. In several brief periods, the Sun coincided exactly with the S-indices of inactive ("flat", presumed Maunder Minimum-type) solar analogues of the Mt. Wilson sample; at the same time, the solar visible surface was also free of any plages or remaining weak activity regions. The corresponding minimum Ca II K flux of the quiet Sun and of the presumed Maunder Minimum-type stars in the Mt. Wilson sample are found to be identical to the corresponding Ca II K chromospheric basal flux limit. Conclusions: We conclude that the quiet-Sun chromosphere is a universal phenomenon among inactive stars. Its mixed-polarity magnetic field, generated by a local, "fast" turbulent dynamo finally provides a natural explanation for the minimal soft X-ray emission observed for inactive stars. Given such a local dynamo also works for giant chromospheres, albeit on larger length scales, i.e., l ~ R/g, with R and g as stellar radius and surface gravity, respectively, the existence of giant spicular phenomena and the guidance of mechanical energy toward the acceleration zone of cool stellar winds along flux-tubes have now become traceable.Comment: 6 pages, 4 figures; Astronomy & Astrophysics (Research Note), in pres