The relative importance of land use and climatic change in Alpine catchments   总被引：1，自引：0，他引：1  

Annett Wolf  Patrick Lazzarotto  Harald Bugmann 《Climatic change》2012,111(2):279-300

Carbon storage and catchment hydrology are influenced both by land use changes and climatic changes, but there are few studies addressing both responses under both driving forces. We investigated the relative importance of climate change vs. land use change for four Alpine catchments using the LPJ-GUESS model. Two scenarios of grassland management were calibrated based on the more detailed model PROGRASS. The simulations until 2100 show that only reforestation could lead to an increase of carbon storage under climatic change, whereby a cessation of carbon accumulation occurred in all catchments after 2050. The initial increase in carbon storage was attributable mainly to forest re-growth on abandoned land, whereas the stagnation and decline in the second half of the century was mainly driven by climate change. If land was used more intensively, i.e. as grassland, litter input to the soil decreased due to harvesting, resulting in a decline of soil carbon storage (1.2−2.9 kg C m^–2) that was larger than the climate-induced change (0.8–1.4 kg C m⁻²). Land use change influenced transpiration both directly and in interaction with climate change. The response of forested catchments diverged with climatic change (11–40 mm increase in AET), reflecting the differences in forest age, topography and water holding capacity within and between catchments. For grass-dominated catchments, however, transpiration responded in a similar manner to climate change (light management: 23–32 mm AET decrease, heavy management: 29–44 mm AET decrease), likely because grassroots are concentrated in the uppermost soil layers. Both the water and the carbon cycle were more strongly influenced by land use compared to climatic changes, as land use had not only a direct effect on carbon storage and transpiration, but also an indirect effect by modifying the climate change response of transpiration and carbon flux in the catchments. For the carbon cycle, climate change led to a cessation of the catchment response (sink/source strength is limited), whereas for the water cycle, the effect of land use change remains evident throughout the simulation period (changes in evapotranspiration do not attenuate). Thus we conclude that management will have a large potential to influence the carbon and water cycle, which needs to be considered in management planning as well as in climate and hydrological modelling.  相似文献   

Relative clustering and the joint halo occupation distribution of red sequence and blue-cloud galaxies in COMBO-17     

P. Simon  M. Hetterscheidt  C. Wolf  K. Meisenheimer  H. Hildebrandt  P. Schneider  M. Schirmer  T. Erben 《Monthly notices of the Royal Astronomical Society》2009,398(2):807-831

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The STAGES view of red spirals and dusty red galaxies: mass-dependent quenching of star formation in cluster infall     

Christian Wolf  Alfonso Aragón-Salamanca  Michael Balogh  Marco Barden  Eric F. Bell  Meghan E. Gray  Chien Y. Peng  David Bacon  Fabio D. Barazza  Asmus Böhm  John A. R. Caldwell  Anna Gallazzi  Boris Häußler  Catherine Heymans  Knud Jahnke  Shardha Jogee  Eelco van Kampen  Kyle Lane  Daniel H. McIntosh  Klaus Meisenheimer  Casey Papovich  Sebastian F. Sánchez  y Taylor  Lutz Wisotzki  Xianzhong Zheng 《Monthly notices of the Royal Astronomical Society》2009,393(4):1302-1323

We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of  σ _cz ≈ 2000 km s⁻¹  . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of  log  M _*/M_⊙=[10, 11]  where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At  log  M _*/M_⊙ < 10  , such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on spirals play a minor role; despite being dust reddened they form only a small fraction of spirals independent of environment.  相似文献   

Magnetically-regulated fragmentation induced by nonlinear flows and ambipolar diffusion     

Shantanu Basu  Glenn E. Ciolek  Wolf B. Dapp  James Wurster 《New Astronomy》2009,14(5):483-495

We present a parameter study of simulations of fragmentation regulated by gravity, magnetic fields, ambipolar diffusion, and nonlinear flows. The thin-sheet approximation is employed with periodic lateral boundary conditions, and the nonlinear flow field (“turbulence”) is allowed to freely decay. In agreement with previous results in the literature, our results show that the onset of runaway collapse (formation of the first star) in subcritical clouds is significantly accelerated by nonlinear flows in which a large-scale wave mode dominates the power spectrum. In addition, we find that a power spectrum with equal energy on all scales also accelerates collapse, but by a lesser amount. For a highly super-Alfvénic initial velocity field with most power on the largest scales, the collapse occurs promptly during the initial compression wave. However, for trans-Alfvénic perturbations, a subcritical magnetic field causes a rebound from the initial compression, and the system undergoes several oscillations before runaway collapse occurs. Models that undergo prompt collapse have highly supersonic infall motions at the core boundaries. Cores in magnetically subcritical models with trans-Alfvénic initial perturbations also pick up significant systematic speeds by inheriting motions associated with magnetically-driven oscillations. Core mass distributions are much broader than in models with small-amplitude initial perturbations, although the disturbed structure of cores that form due to nonlinear flows does not guarantee subsequent monolithic collapse. Our simulations also demonstrate that significant power (if present initially) can be maintained with negligible dissipation in large-scale compressive modes of a magnetic thin sheet, in the limit of perfect flux freezing.  相似文献   

Detecting protoplanets with ALMA     

Sebastian Wolf 《Astrophysics and Space Science》2008,313(1-3):109-112

Theoretical investigations show that planet-disk interactions cause structures in circumstellar disks, which are usually much larger in size than the planet itself and thus more easily detectable. The specific result of planet-disk interactions depends on the evolutionary stage of the disk. Exemplary signatures of planets embedded in disks are gaps and spiral density waves in the case of young, gas-rich protoplanetary disks and characteristic asymmetric density patterns in debris disks. Numerical simulations convincingly demonstrate that high-resolution imaging performed with observational facilities which are already available or will become available in the near future will allow to trace these “fingerprints” of planets in protoplanetary and debris disks. These observations will provide a deep insight into specific phases of the formation and early evolution of planets in circumstellar disks. In this context, the Atacama Large Millimeter Array (ALMA) will play a crucial role by allowing to trace features in disks which are indicative for various stages of the formation and early evolution of planets in circumstellar disks.  相似文献   

The dark matter environment of the Abell 901/902 supercluster: a weak lensing analysis of the HST STAGES survey     

Catherine Heymans  Meghan E. Gray  Chien Y. Peng  Ludovic Van Waerbeke  Eric F. Bell  Christian Wolf  David Bacon  Michael Balogh  Fabio D. Barazza  Marco Barden  Asmus Böhm  John A. R. Caldwell  Boris Häußler  Knud Jahnke  Shardha Jogee  Eelco van Kampen  Kyle Lane  Daniel H. McIntosh  Klaus Meisenheimer  Yannick Mellier  Sebastian F. Sánchez  y N. Taylor  Lutz Wisotzki  Xianzhong Zheng 《Monthly notices of the Royal Astronomical Society》2008,385(3):1431-1442

We present a high-resolution dark matter reconstruction of the   z = 0.165  Abell 901/902 supercluster from a weak lensing analysis of the Hubble Space Telescope STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901α. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'.  相似文献   

Impact of light regimes on productivity patterns of benthic microbial mats in an antarctic lake: a modeling study     

Moorhead DL  Wolf CF  Wharton RA 《Limnology and oceanography》1997,42(7):1561-1569

Filamentous cyanobacteria often dominate benthic microbial communities of antarctic lakes and usually exhibit saturation of photosynthesis at light intensities approximately 100 microEinst m-2 s-1. Incident light regimes are controlled by ice and snow accumulations overlaying water columns during much of the year. Thus, light availability to microbial mats is often below saturation intensity and is strongly influenced by modest changes in climatic factors. A model of net primary production for benthic mat communities of the subantarctic Sombre Lake, Signy Island, was developed (1) to evaluate depth-specific productivities of mat communities, (2) to test the relative importances of model parameters to mat production, and (3) to explore the potential impacts of climate change on mat production as manifested through changes in light regime. Simulated rates of net primary production corresponded to observations on a daily basis (approximately 1-4 micrograms C fixed mg-1 ash-free DW of mat d-1) but were an order of magnitude lower than estimates of net annual production based on field measurements (< or = 3 vs. 11-45 g C m-2 yr-1, respectively). Close examination suggested that the simulated values were more plausible. A detailed sensitivity analysis of model behavior revealed that variations in the time of ice and snow melt in spring accounted for 40-60% of the total variation in model behavior, emphasizing the importance of climatic factors to net primary production of mat communities and the sensitivity of mat production to climate change.  相似文献   

APPLICATION OF A PROCEDURE FOR STATISTICAL ASSESSMENT OF POINTS ON A LINE     

Wolf Roder 《The Professional geographer》1974,26(3):283-290

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Guaszscher Algorithmus (Doolittle-Methode) und Boltzsches Entwicklungsverfahren     

H. Wolf 《Journal of Geodesy》1952,26(4):445-452

Zusammenfassung Die jüngsten Arbeiten von Prof.Jenne (Potsdam) über die unbestimmte Aufl?sung der Normalgleichungen für Winkelbedingungen und eine von Dr.Dupuy 1948 aufgeworfene Frage geben Anla\ zu einer Gegenüberstellung der verschiedenen Verfahren zur Aufl?sung von Normalgleichungen, insbes. des Gau\schen Algorithmus und des Boltzschen Entwicklungsverfahrens. Im Hinblick auf den beachtlichen Vorsprung im Aufl?sungsproze?, den die Mitbenützung der fertig ausgerechneten Korrelatentabellen für die Dreieckswinkelgleichungen gew?hren, kommt man zu dem Schlu?, da? es weniger der Gegensatz als vielmehr die geschickte Verbindung der beiden vorgenannten Verfahren ist, welche eine besondere Beachtung und Würdigung verdient.

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Summary The most recent work of ProfessorJenne (of Potsdam) on the algebraical solution of normal angle condition equations, and on a question raised in 1948 by DrDupuy, gives us the opportunity of comparing various methods for the solution of normal equations, in particular the Gaussian algorithm and Boltz’s development method. Having taken account of the valuable saving introduced, in the methods of solution, by the use of tables of correlatives, calculated from the angle equations, one arrives at the conclusion that there is some value in giving detailed consideration to the judicious combination of the two methods mentioned above—rather than drawing attention to their differences.

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Resumen Los trabajos más recientes del ProfesorJenne (de Potsdam) sobre la resolución indeterminada de las ecuaciones normales de condición para los ángulos así como una cuestión planteada en 1948 por el Dr.Dupuy, nos proporcionan la ocasión de comparar los diversos métodos de resolución de las ecuaciones normales, en particular el algoritmo deGauss y el método de desarrollo deBoltz. Teniendo en cuenta el progreso notable llevado al proceso de resolución, por el empleo de los correlativos, calculados del todo con las ecuaciones de ángulos, se llega a la conclusión que conviene prestar una atención y una consideración particulares a la feliz combinación de los dos métodos antes mencionados, mucho más que a la oposición de los mismos.

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Résumé Les travaux les plus récents du ProfesseurJenne (de Potsdam) sur larésolution indéterminée des équations normales de condition aux angles et une question soulevée en 1948 par le DrDupuy nous donnent l’occasion de comparer les diverses méthodes de résolution des équations normales, en particulier l’algorithme deGauss et la méthode de développement deBoltz. Compte tenu du progrès notable apporté, dans le processus de résolution, par l’emploi des corrélatifs tout calculés des équations aux angles, on arrive à la conclusion qu’il convient d’accorder une attention et une considération particulières à l’adroite combinaison des deux méthodes ci-dessus mentionnées—beaucoup plus qu’à leur opposition.

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Sommario I lavori più recenti del prof.Jenne (di Potsdam) sulla risoluzione indeterminata delle equazioni normali·di condizione agli angoli, ed una questione sollevata dal Dr.Dupuy, ci offrono lo spunto per confrontare i diversi metodi di risoluzione delle equazioni normali, in particolare l’algoritmo diGauss ed il metodo di sviluppo diBoltz. Tenuto conto del notevole progresso apportato, nel procedimento di risoluzione, dall’impiego dei correlativi precalcolati delle equazioni agli angoli, si giunge alla conclusione che conviene rivolgere l’attenzione alla possibilità di accordare, piuttosto che di contrapporre, i due metodi menzionati.

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Characterisation of Fulvic Acids and Glycyrrhizic Acid by Time‐of‐Flight Secondary Ion Mass Spectrometry     

Wilfried Szymczak  Manfred Wolf  Klaus Wittmaack 《洁净——土壤、空气、水》2001,28(7):350-358

Fulvic acids of different origin, spray deposited on polished silicon after dissolution in high‐purity water without any additives, were analysed by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) in combination with oblique 24...36 keV SF₅⁺ ion bombardment. The observed, highly reproducible mass spectra cover more than five orders of magnitude in dynamic range, without background subtraction. Apart from lines due to atomic ions and low‐mass ion fragments, the mass spectra exhibit broad maxima between m/z 200...350, mainly due to a beat‐like superposition of lines at every single mass number, up to at least m/z 400. In the negative ion spectra the beats have a spacing of m/z 14, corresponding to a CH₂‐unit. The high‐mass tails of the spectra extend well beyond m/z 5000, with similar slopes in the positive and the negative ion mass spectra. The negative spectra appear to be less affected by fragmentation products than the positive spectra. Fulvic acids (FAs) of different origin show distinctly different spectra, with mean masses ranging between m/z ≈ 450 and 580 (for a low‐mass cut‐off m/z 150). To further verify the ability of TOF‐SIMS to detect molecules and clusters with masses significantly above the maxima of the FA spectra, samples of glycyrrhizic acid (GA, as GA ammonium salt with molecular weight 840) were also analysed. Parent ions as well as multimers (GA)_n were observed as positive and negative ions, up to n = 4 (m/z 3320). The results are compared with spectra recently obtained by other mass spectrometric techniques.  相似文献