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  • 1
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Synthesis of results from several Arctic and boreal research programmes provides evidence for the strong role of high-latitude ecosystems in the climate system. Average surface air temperature has increased 0.3 °C per decade during the twentieth century in the western North American Arctic and boreal forest zones. Precipitation has also increased, but changes in soil moisture are uncertain. Disturbance rates have increased in the boreal forest; for example, there has been a doubling of the area burned in North America in the past 20 years. The disturbance regime in tundra may not have changed. Tundra has a 3–6-fold higher winter albedo than boreal forest, but summer albedo and energy partitioning differ more strongly among ecosystems within either tundra or boreal forest than between these two biomes. This indicates a need to improve our understanding of vegetation dynamics within, as well as between, biomes. If regional surface warming were to continue, changes in albedo and energy absorption would likely act as a positive feedback to regional warming due to earlier melting of snow and, over the long term, the northward movement of treeline. Surface drying and a change in dominance from mosses to vascular plants would also enhance sensible heat flux and regional warming in tundra. In the boreal forest of western North America, deciduous forests have twice the albedo of conifer forests in both winter and summer, 50–80% higher evapotranspiration, and therefore only 30–50% of the sensible heat flux of conifers in summer. Therefore, a warming-induced increase in fire frequency that increased the proportion of deciduous forests in the landscape, would act as a negative feedback to regional warming.Changes in thermokarst and the aerial extent of wetlands, lakes, and ponds would alter high-latitude methane flux. There is currently a wide discrepancy among estimates of the size and direction of CO2 flux between high-latitude ecosystems and the atmosphere. These discrepancies relate more strongly to the approach and assumptions for extrapolation than to inconsistencies in the underlying data. Inverse modelling from atmospheric CO2 concentrations suggests that high latitudes are neutral or net sinks for atmospheric CO2, whereas field measurements suggest that high latitudes are neutral or a net CO2 source. Both approaches rely on assumptions that are difficult to verify. The most parsimonious explanation of the available data is that drying in tundra and disturbance in boreal forest enhance CO2 efflux. Nevertheless, many areas of both tundra and boreal forests remain net sinks due to regional variation in climate and local variation in topographically determined soil moisture. Improved understanding of the role of high-latitude ecosystems in the climate system requires a concerted research effort that focuses on geographical variation in the processes controlling land–atmosphere exchange, species composition, and ecosystem structure. Future studies must be conducted over a long enough time-period to detect and quantify ecosystem feedbacks.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 34 (1985), S. 3-26 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Die zweidimensionale, numerische Simulierung der Seebrisenentwicklung über einer großen Sandbank an der Nordseeküste Deutschlands wird beschrieben. Das hier angewandte Modell enthält eine detaillierte Behandlung der Bodenfeuchte, welche eine Auswertung des Effektes differenzierter Oberflächencharakteristika auf die Luftströmung erlaubt. Rechnungsresultate zeigen, daß der Kontrast zwischen Sandbank und benachbartem, trockenem Land, die gezeitenbewirkte Überflutung der Sandbank und die nach Osten vorrückende Seebrise der Ostsee eine wichtige Rolle in der Entwicklung von mesoskalaren Strömungsverteilungen im Gebiet der Sandbank spielen.
    Notes: Summary Two-dimensional numerical simulations of sea breeze development over a large sandbar on the North Sea coast of Germany are reported. The numerical model used in these experiments contains a detailed treatment of soil moisture, which allows evaluation of the effects of differential surface characteristics on the airflow pattern. Results of the simulations indicate that the contrast between the moist sandbar and adjacent dry land, the tidal inundation of the sandbar, and the westward penetration of the Baltic sea breeze play important roles in the development of mesoscale airflow patterns in the sandbar region.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 29 (1980), S. 1-40 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Das Zusammenwachsen oder Verschmelzen von Cumulus-Wolken wird als einer der Hauptgründe für ihr Wachstum sowie für ihren Einfluß auf ihre Umgebung und auf die durch sie bewerkstelligten Transportprozesse angesehen. Das Verschmelzen von Cumulus-Schauern wird auf Grund der von einem kalibrierten und digitisierten 10-cm-Radar empfangenen Echos definiert. Das Radargerät überblickt eine Fläche von 0.9×105 km2 im Süden Floridas (U. S. A.), die ein Exerimentalgebiet von 1.3×104 km2 für randomisierte Wolkenimpfung umgibt. Eine detaillierte physikalische und statistische Studie für drei relativ ungestörte Tage ohne Wolkenimpfung während des Sommers 1973 wird hiermit vorgelegt. Der trockenste dieser Tage war willkürlich als Kontrolltag für das Wolkenimpfungsexperiment gewählt worden. Verschmelzungsprozesse weisen um mehr als eine Größenordnung mehr Niederschlag auf als unverschmolzene Echos, während Verschmelzungen von Verschmelzungen (Verschmelzungen zweiter Ordnung) nochmals eine Größenordnung mehr Regen ergeben. An den drei untersuchten Tagen produzierten verschmolzene Systeme ungefähr 86% des über dem Untersuchungsgebiet beobachteten Regens. Andauer, Echoausmaß und Niederschlagshöhe werden für verschmolzene und unverschmolzene Wolkensysteme verglichen. Jeder Tag wird individuell analysiert, wobei eine Korrelation zwischen Wolkenorganisation und Niederschlagsbetrag angedeutet wird, die auch von anderen, kurz erwähnten Forschungsarbeiten bekräftigt wurde. Ort und Zeit des Verschmelzens hängen von der Seewind-Konvergenzzone ab, welche durch das mesoskalare Rechenmodell der University of Virginia gut vorhergesagt wurde. Eine physikalische Hypothese über die Wichtigkeit der Absinkbewegung während des Cumulus-Verschmelzungsprozesses wird dargelegt. Die Bedeutung der Verschmelzungsvorgänge für die Hydrologie, für die künstliche Wetterbeeinflussung und für den großräumigen Einfluß konvektiver Wolken wird diskutiert.
    Notes: Summary Joining together or merging is postulated to be a major way in which convective clouds become larger, enhancing their transports and impacts upon their environment. Cumulus shower merger is defined in terms of echoes from a calibrated digitized 10-cm radar reviewing a 0.9×105 km2 area in south Florida, U. S. A., which encompasses a 1.3×104 km2 experimental area for randomized seeding. A detailed physical and statistical study is reported for three relatively undisturbed untreated days in the summer of 1973, the driest of which was a randomly selected control day for the experiment. Mergers are found to produce more than an order of magnitude more rain than unmerged echoes, while mergers of mergers (second order mergers) produce still an order of magnitude more rain. On the three days studied, merged systems produced about 86% of the rainfall over the area. Duration, echo area and rain depths are also compared for merged and unmerged systems. Each day is then analyzed individually, indicating a correlation between organization and rain amount, confirmed by other research reviewed briefly. The location and time of merger is related to the seabreeze convergence zones as predicted by the University of Virginia Mesoscale Model with overall good agreement. Physical hypotheses suggesting the importance of downdrafts in cumulus merging are developed. The relevance of mergers to hydrology, weather modification and the large-scale impacts of convective clouds is discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 40 (1989), S. 189-193 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Generalized hydrostatic and geostrophic equations can be derived from the equations in the terrain-following framework. The generalized hydrostatic equation permits some non-hydrostatic motions (as obtained from a Cartesian framework) to remain when a non-zero slope exists. Correspondingly, the generalized geostrophic wind permits a horizontal divergent component (in addition to divergence caused by the change of Coriolis parameter with latitude) to occur when the slope angle is not zero.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary This paper presents a range of applications of the Regional Atmospheric Modeling System (RAMS), a comprehensive mesoscale meterological modeling system. Applications discussed in this paper include large eddy simulations (LES) and simulations of thunderstorms, cumulus fields, mesoscale convective systems, mid-latitude cirrus clouds, winter storms, mechanically- and thermally-forced mesoscale systems, and mesoscale atmospheric disperision. A summary of current RAMS options is also presented. Improvements to RAMS currently underway include refinements to the cloud radiation, cloud microphysics, cumulus, and surface soil/vegetative parameterization schemes, the parallelization of the code, development of a more versatile visualization capability, and research into meso-α-scale cumulus parameterization.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 37 (1987), S. 1-10 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this paper we show using a three-dimensional mesoscale model that terrain forcing has a major effect on the observed snowfall distribution under upslope conditions in northeast Colorado. Two upslope snowstorms (in 1982 and in 1985) were simulated. The effects are strongly dependent on the orientation of the prevailing wind with respect to terrain orientation. It is suggested that an approach such as discussed in this paper could be used in a forecasting mode, combined with traditional tools such as the NWS Limited Fine Mesh Model (LFM) or Nested Grid Model (NGM). In both of these cases the LFM correctly predicted the development of these storms. However, due to its much coarser resolution it was unable to resolve the terrain-forced variation evident in the simulations presented here.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 39 (1988), S. 184-196 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this paper, analytic solutions of the nonhydrostatic and hydrostatic forms of Long's model were obtained under two different sets of vertical boundary conditions: The first uses a sumusoidal obstacle at the lower boundary and a rigid-lid top for the upper boundary. The second set applies an isolated obstacle of the “Witch of Agnesi” type at the lower boundary, while still using a rigid lid at the top. Following the solution evaluations, comparisons between the nonhydrostatic and hydrostatic solutions were processed in order to describe several influences introduced by using the hydrostatic assumption in this model. Through comparisons we have found that, in the case of a sinusoidal lower boundary condition, the hydrostatic solution is obtained as the zero mode of the nonhydrostatic solution. The influence of the hydrostatic assumption on the model solution is trivial in this case. When an isolated lower boundary condition is applied, however, the solutions illustrate dramatic differences, showing the significance of the effect of hydrostatic assumption on this model's solutions. These effects vary considerably with the model parameters as well. The comparison results also reveal that the realization of the hydrostatic assumption in this model's solutions is accomplished through the vertical boundary conditions used in the model evaluations.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International journal of biometeorology 31 (1987), S. 45-55 
    ISSN: 1432-1254
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract A coupled atmosphere-soil model was applied in order to evaluate the impact of soil wetness on human stress in the absence of horizontal gradients in moisture. The results are illustrated and discussed with consideration to various combinations of wind speed and lower level atmospheric moisture during daylight hours with summer weather conditions. A thermal index composed of the air temperature and wet-bulb temperature does not show major changes as a function of variation of soil mosture. When wind speed and solar radiation are also considered, in a more detailed thermal index, relatively wet soil is associated with the optimal thermal comfort.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of biometeorology 37 (1993), S. 96-100 
    ISSN: 1432-1254
    Keywords: Halophytes — Effect on weather ; arid region climate modification ; irrigation — Effect on weather ; vegetation — Effect on weather ; Deliberate climate modification by vegetation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract The practicality of modifying climate in arid regions through irrigation has up to now been constrained by the availability of fresh water with which to grow crops. The present results suggest a new paradigm: the use of salt water to grow halophyte crops and modify local climate along coastal deserts and other arid regions where saline water supplies are available.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nonlinear science 2 (1992), S. 263-292 
    ISSN: 1432-1467
    Keywords: biosystem behavior ; Earth temperature ; diffusion of the temperature ; periodic and linear variation of luminosity ; stationary solutions ; asymptotic local and global stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary A detailed mathematical analysis is presented of the model of Daisyworld, proposed by Watson and Lovelock. The stationary solutions of a resulting quartic system of ODEs are examined and their local and global attractivity is proved. The model shows, in a suitable range of values of the albedo and of the diffusion of the temperature, a mitigation of the climate in response to luminosity perturbations. The feedback between the biological components and the Earth's climate can be so efficient that the temperature of the Earth will stay practically constant even under substantial variations of the solar luminosity.
    Type of Medium: Electronic Resource
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