GLORIA

GEOMAR Library Ocean Research Information Access

X
feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
  • 1
    Digitale Medien
    Digitale Medien
    Intermittency, local isotropy, and non-Gaussian statistics in atmospheric surface layer turbulence (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 2480-2492 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Orthonormal wavelet expansions are applied to atmospheric surface layer velocity and temperature measurements above a uniform bare soil surface that exhibit a long inertial subrange energy spectrum. In order to investigate intermittency effects on Kolmogorov's theory, a direct relation between the nth-order structure function and the wavelet coefficients is derived. This relation is used to examine deviations from the classical Kolmogorov theory for velocity and temperature in the inertial subrange. The local nature of the orthonormal wavelet transform in physical space aided the identification of events directly contributing to intermittency buildup at inertial subrange scales. These events occur at edges of large eddies and contaminate the Kolmogorov inertial subrange scaling. By suppressing these events, the statistical structure of the inertial subrange for the velocity and temperature, as described by Kolmogorov's theory, is recovered. The suppression of intermittency on the nth-order structure function is carried out via a conditional wavelet sampling scheme. The conditioned wavelet statistics reproduced the Kolmogorov scaling (up to n=6) in the inertial subrange and result in a zero intermittency factor. The conditional wavelet statistics for the mixed velocity temperature structure functions are also presented. It was found that the conditional wavelet statistics for these mixed moments result in a thermal intermittency parameter consistent with other laboratory and field measurements. The relationship between Kolmogorov's theory and near-Gaussian statistics for velocity and temperature gradients is also considered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.868196
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 2
    Digitale Medien
    Digitale Medien
    Reduction of forest floor respiration by fertilization on both carbon dioxide-enriched and reference 17-year-old loblolly pine stands (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Elevated atmospheric carbon dioxide (CO2e) increases soil respiration rates in forest, grassland, agricultural and wetland systems as a result of increased growth, root biomass and enhanced biological activity of soil microorganisms. Less is known about how forest floor fluxes respond to the combined effects of elevated CO2 and nutrient amendments; until now no experiments have been in place with large forest trees to allow even preliminary investigations. We investigated changes in forest floor respiration (Sff) in a Pinus taeda L. plantation fumigated with CO2 by using free-air CO2 enrichment (FACE) technology and given nutrient amendments. The prototype FACE apparatus (FACEp; 707 m2) was constructed in 1993, 10 years after planting, on a moderate fertility site in Duke Forest, North Carolina, USA, enriching the stand to 55 Pa (CO2e). A nearby ambient CO2 (CO2a) plot (117 m2) was designated at the inception of the study as a reference (Ref). Both FACEp and Ref plot were divided in half and urea fertilizer was applied to one half at an annual rate of 11.2 g N m−2 in the spring of 1998, 1999 and 2000. Forest floor respiration was monitored continuously for 220 days – March through November 2000 – by using two Automated Carbon Efflux Systems. Thirty locations (491 cm2 each) were sampled in both FACEp and Ref, about half in each fertility treatment. Forest floor respiration was strongly correlated with soil temperature at 5 cm. Rates of Sff were greater in CO2e relative to CO2a (an enhancement of ∼178 g C m−2) during the measurement period. Application of fertilizer resulted in a statistically significant depression of respiration rates in both the CO2a and CO2e plots (a reduction of ∼186 g C m−2). The results suggest that closed canopy forests on moderate fertility sites cycle back to the atmosphere more assimilated carbon (C) than similar forests on sites of high fertility. We recognize the limitations of this non-replicated study, but its clear results offer strong testable hypotheses for future research in this important area.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00630.x
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 3
    Digitale Medien
    Digitale Medien
    Hydrologic balance in an intact temperate forest ecosystem under ambient and elevated atmospheric CO2 concentration (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Abstract Increasing atmospheric CO2 concentration decreases stomatal conductance in many species, but the savings of water from reduced transpiration may permit the forest to retain greater leaf area index (L). Therefore, the net effect on water use in forest ecosystems under a higher CO2 atmosphere is difficult to predict. The free air CO2 enrichment (FACE) facility (n = 3) in a 14-m tall (in 1996) Pinus taeda L. stand was designed to reduce uncertainties in predicting such responses. Continuous measurements of precipitation, throughfall precipitation, sap flux, and soil moisture were made over 3.5 years under ambient (CO2a) and elevated (CO2e) ambient + 200 µmol mol−1). Annual stand transpiration under ambient CO2 conditions accounted for 84–96% of latent heat flux measured with the eddy-covariance technique above the canopy. Under CO2e, P. taeda transpired less per unit of leaf area only when soil drought was severe. Liquidambar styraciflua, the other major species in the forest, used progressively less water, settling at 25% reduction in sap flux density after 3.5 years under CO2e. Because P. taeda dominated the stand, and severe drought periods were of relatively short duration, the direct impact of CO2e on water savings in the stand was undetectable. Moreover, the forest used progressively more water under CO2e, probably because soil moisture availability progressively increased, probably owing to a reduction in soil evaporation caused by more litter buildup in the CO2e plots. The results suggest that, in this forest, the effect of CO2e on transpiration was greater indirectly through enhanced litter production than directly through reduced stomatal conductance. In forests composed of species more similar to L. styraciflua, water savings from stomatal closure may dominate the response to CO2e.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00513.x
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Exposure to an enriched CO2 atmosphere alters carbon assimilation and allocation in a pine forest ecosystem (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: We linked a leaf-level CO2 assimilation model with a model that accounts for light attenuation in the canopy and measurements of sap-flux-based canopy conductance into a new canopy conductance-constrained carbon assimilation (4C-A) model. We estimated canopy CO2 uptake (AnC) at the Duke Forest free-air CO2 enrichment (FACE) study. Rates of AnC estimated from the 4C-A model agreed well with leaf gas exchange measurements (Anet) in both CO2 treatments. Under ambient conditions, monthly sums of net CO2 uptake by the canopy (AnC) were 13% higher than estimates based on eddy-covariance and chamber measurements. Annual estimates of AnC were only 3% higher than carbon (C) accumulations and losses estimated from ground-based measurements for the entire stand. The C budget for the Pinus taeda component was well constrained (within 1% of ground-based measurements). Although the closure of the C budget for the broadleaf species was poorer (within 20%), these species are a minor component of the forest. Under elevated CO2, the C used annually for growth, turnover, and respiration balanced only 80% of the AnC. Of the extra 700 g C m−2 a−1 (1999 and 2000 average), 86% is attributable to surface soil CO2 efflux. This suggests that the production and turnover of fine roots was underestimated or that mycorrhizae and rhizodeposition became an increasingly important component of the C balance. Under elevated CO2, net ecosystem production increased by 272 g C m−2 a−1: 44% greater than under ambient CO2. The majority (87%) of this C was sequestered in a moderately long-term C pool in wood, with the remainder in the forest floor–soil subsystem.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00662.x
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 5
    Digitale Medien
    Digitale Medien
    Soil fertility limits carbon sequestration by forest ecosystems in a CO 2 -enriched atmosphere (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 411 (2001), S. 469-472 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] Northern mid-latitude forests are a large terrestrial carbon sink. Ignoring nutrient limitations, large increases in carbon sequestration from carbon dioxide (CO2) fertilization are expected in these forests. Yet, forests are usually relegated to sites of moderate to poor fertility, ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/35078064
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 6
    Digitale Medien
    Digitale Medien
    Mechanisms of long-distance dispersal of seeds by wind (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 418 (2002), S. 409-413 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] Long-distance dispersal (LDD) is central to species expansion following climate change, re-colonization of disturbed areas and control of pests. The current paradigm is that the frequency and spatial extent of LDD events are extremely difficult to predict. Here we show that mechanistic models ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/nature00844
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 7
    Digitale Medien
    Digitale Medien
    A model for sensible heat flux probability density function for near-neutral and slightly-stable atmospheric flows (1994)
    Springer
    Boundary layer meteorology 71 (1994), S. 1-20 
    Details
    ISSN: 1573-1472
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract The probability density function for sensible heat flux was measured above a uniform dry lakebed (Owens lake) in Owens Valley, California. It was found that for moderately stable to near neutral atmospheric stability conditions, the probability density function exhibits well defined exponential tails. These exponential tails are consistent with many laboratory boundarylayer measurements and numerical simulations. A model for the sensible heat flux probability density function was developed and tested. A key assumption in the model derivation was the near Gaussian statistics of the vertical velocity and temperature fluctuations. This assumption was verified from time series measurements of temperature and vertical velocity. The parameters for the sensible heat flux probability density function model were also derived from mean meteorological and surface conditions using surface-layer similarity theory. It was found that the best agreement between modeled and measured sensible heat flux probability density function was at the tails. Finally, a relation between the intermittency parameter, the probability density function, and the mean meteorological conditions was derived. This relation rigorously links the intermittency parameter to mean meteorological conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00709217
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 8
    Digitale Medien
    Digitale Medien
    Local isotropy and anisotropy in the sheared and heated atmospheric surface layer (1995)
    Springer
    Boundary layer meteorology 72 (1995), S. 123-148 
    Details
    ISSN: 1573-1472
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations, we investigated directly the sources of anisotropy. These sources, in a daytime desert-like climate, include: (1) direct interaction between the large-scale and small-scale eddy motion, and (2) thermal effects on the small-scale eddy motion. In order to explore these two anisotropy sources, we developed statistical measures that are sensitive to such interactions. It was found that the large-scale/small-scale interaction was significant in the inertial subrange up to 3 decades below the production scale, thus reducing the validity of the local isotropy assumption. The anisotropy generated by thermal effects was also significant and comparable in magnitude to the former anisotropy source. However, this thermal anisotropy was opposite in sign and tended to counteract the anisotropy generated by the large-scale/smallscale interaction. The thermal anisotropy was attributed to organized ramp-like patterns in the temperature measurements. The impact of this anisotropy cancellation on the dynamics of inertial subrange eddy motion was also considered. For that purpose, the Kolmogorov-Obukhov structure function equation, as derived from the Navier-Stokes equations for locally isotropic turbulence, was employed. The Kolmogorov-Obukhov structure function equation in conjunction with Obukhov's constant skewness closure hypothesis reproduced the measured second- and third-order structure functions. Obukhov's constant skewness closure scheme, which is also based on the local isotropy assumption, was verified and was found to be in good agreement with the measurements. The accepted 0.4 constant skewness value derived from grid turbulence experiments overestimated our measurements. A suggested 0.26 constant skewness value, which we derived from Kolmogorov's constant, was found to be adequate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00712392
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 9
    Digitale Medien
    Digitale Medien
    The spatial structure of turbulence at production wavenumbers using orthonormal wavelets (1995)
    Springer
    Boundary layer meteorology 75 (1995), S. 81-108 
    Details
    ISSN: 1573-1472
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract Orthonormal wavelet expansions are applied to surface-layer measurements of vertical wind speed under various atmospheric, stability conditions. The orthonormal wavelet transform allows for the unfolding of these measurements into space and scale simultaneously to reveal the large intermittent behavior in space for the turbulent production wavenumbers. Both Fourier and wavelet power spectra indicated the existence of a −1 power law for the vertical velocity measurements at the production wavenumbers. The −1 power law in the turbulent production range was derived from surface-layer similarity theory. A dimensionless skewness, structure function is applied to the wavelet decomposed vertical velocity field to trace the destruction of the shear-or buoyancy-induced anisotropy under various stability conditions. The structure skewness function revealed shear- or buoyancy-induced eddy asymmetry dependence on stability at each scale within the −1 power-law wavenumber range with more isotropy during propagation from smaller to larger wavenumbers. The asymmetry of these events at the turbulent production wavenumbers appeared very localized in space, as well as in scale, and could be described with a simple eddy-overturning model. It is demonstrated that the wavelet transform is suitable for such analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00721045
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 10
    Digitale Medien
    Digitale Medien
    A Note on the Flux-Variance Similarity Relationships for Heat and Water Vapour in the Unstable Atmospheric Surface Layer (1999)
    Springer
    Boundary layer meteorology 90 (1999), S. 327-338 
    Details
    ISSN: 1573-1472
    Schlagwort(e): Atmospheric surface layer ; Closure models ; Flux variance method ; Scalar transport ; Scalar variance similarity functions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract Atmospheric surface layer (ASL) experiments over the past 10 years demonstrate that the flux-variance similarity functions for water vapour are consistently larger in magnitude than their temperature counterpart. In addition, latent heat flux calculations using the flux-variance method do not compare as favorably to eddy- correlation measurements when compared to their sensible heat counterpart. These two findings, in concert with measured heat to water vapour transport efficiencies in excess of unity, are commonly used as evidence of dissimilarity between heat and water vapour transport in the unstable atmospheric surface layer. In this note, it is demonstrated that even if near equality in flux-profile similarity functions for heat and water vapour is satisfied, the flux-variance similarity functions for water vapour are larger in magnitude than temperature for a planar, homogeneous, unstably-stratified turbulent boundary-layer flow.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1001747925158
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...