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  • 1
    Series available for loan
    Series available for loan
    An empirical assessment of refraction error in leveling as a function of survey order and environment (1994)
    Washington, DC : United States Gov. Print. Off.
    Associated volumes
    Details Availability
    Call number: SR 90.0001(2114)
    In: U.S. Geological Survey bulletin
    Type of Medium: Series available for loan
    Pages: V, 50 S.
    Series Statement: U.S. Geological Survey bulletin 2114
    Language: English
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    Calculation of velocity skewness in real and artificial plant canopies (1987)
    Springer
    Boundary layer meteorology 39 (1987), S. 315-332 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Wind velocities within a plant canopy are much more strongly skewed than those of the air flow above. We have examined the governing Eulerian equations for the velocity products u′ i, u′ j u′k using data from a wind tunnel study with an artificial canopy consisting of an array of 5 cm lengths of monofilament fishing line, and from measurements in corn (Zea mays L). Simple parameterizations for pressure-velocity correlations, and for the quadruple velocity products allowed reasonably accurate calculations of the third moments using measured profiles of the mean velocity, variance and covariance fields. Comparisons of individual terms in the rate equations for ovu′ i, u′ j u′ krevealed that diffusion (from above) and mean shear were most important in creating large skewness in the canopy. A drag term also contributed but was of lesser importance. These terms were balanced by return-to-isotropy and a turbulence interaction term. A quasi-Gaussian approximation considerably underestimated the magnitude of the fourth moments within the canopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00125141
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  • 3
    Electronic Resource
    Electronic Resource
    Boundary-layer flow structures associated with particle reentrainment (1993)
    Springer
    Boundary layer meteorology 65 (1993), S. 255-272 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Measurements of near-surface longitudinal and vertical wind velocity components associated with particle reentrainment from a flat surface have been examined in a wind tunnel. Sparsely covered particle beds were used to assure that observed reentrainment events resulted primarily from the action of fluid forces. Characteristic velocity patterns were found to be associated with a majority of particle reentrainment events examined. These characteristics have been categorized and examined as ensemble averages. The flow pattern most frequently observed during particle reentrainment was termed Ejection-Sweep (E-S) and is very similar to organized fluid motions previously observed in laboratory flows and in the atmospheric boundary layer. A simple two-tiered E-S pattern recognition scheme is described which strives to identify particle reentrainment events objectively based on flow characteristics alone. The first step is to identify potential E-S patterns using criteria which identify a characteristic longitudinal acceleration, and the second step is to use threshold values of pattern characteristics to accept or reject these first-tier patterns. Pattern recognition results are presented in terms of the ability to identify reentrainment events versus false identifications, and show an exponential growth in false identifications with an increasing number of reentrainment events identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705529
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  • 4
    Electronic Resource
    Electronic Resource
    Pseudo-wavelet analysis of turbulence patterns in three vegetation layers (1995)
    Springer
    Boundary layer meteorology 72 (1995), S. 177-204 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Ramp patterns in scalar traces such as temperature are the signature of coherent structures. A pseudo-wavelet analysis technique was developed in which ideal saw-tooth patterns of varying size were used as basis functions and fitted to temperature and velocity data. Data recorded from three very different vegetation stands were examined in this study. It was found that the most probable structure duration for the forest canopy was in the range 35–40 s, for the orchard canopy it was 20–25 s and for the maize it was 15–20 s. When expressed in non-dimensional form, the structure duration probability distribution for the maize canopy was about a decade larger than for the forest canopy, with the orchard canopy intermediate. The mean eddy duration versus wind shear relation falls on a narrow band for all three canopies, indicating that wind shear at the canopy top is the determining factor for the scale of the coherent eddies. The inverse of duration and intermittency of coherent structures exhibits a tendency of independence from wind shear at higher wind shear values. Coherent structures transport heat in a more efficient way than do smaller scale, less coherent motions. In all the canopies, the heat flux fractions associated with coherent structures are at least 10% higher than the corresponding time fraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712394
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  • 5
    Electronic Resource
    Electronic Resource
    Turbulent Statistics of Neutrally Stratified Flow Within and Above a Sparse Forest from Large-Eddy Simulation and Field Observations (1998)
    Springer
    Boundary layer meteorology 88 (1998), S. 363-397 
    Details
    ISSN: 1573-1472
    Keywords: Coherent structure ; Field observation ; Forest ; Large-eddy simulation (LES) ; Neutrally stratified shear-driven flow ; Turbulent statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Turbulent statistics of neutrally stratified shear-driven flow within and above a sparse forest canopy are presented from a large-eddy simulation (LES) and compared with those from observations within and above a deciduous forest with similar height and foliage density. First- and second-order moments from the LES agree with observations quite well. Third-order moments from the LES have the same sign and similar vertical patterns as those from the observations, but the LES yields smaller magnitudes of such higher-order moments. Turbulent spectra and cospectra from the LES agree well with observations above the forest. However, at the highest frequencies, the LES spectra have steeper slopes than observations. Quadrant and conditional analyses of the LES resolved-scale flow fields also agree with observations. For example, both LES and observation find that sweeps are more important than ejections for the transport of momentum within the forest, while inward and outward interaction contributions are both small, except near the forest floor. The intermittency of the transport of momentum and scalar increases with depth into the forest. Finally, ramp structures in the time series of a passive scalar at multiple levels within and above the forest show similar features to those measured from field towers. Two-dimensional (height-time cross-section) contours of the passive scalar and wind vectors show sweeps and ejections, and the characteristics of the static pressure perturbation near the ground resemble those deduced from field tower-based measurements. In spite of the limited grid resolution (2 m × 2 m × 2 m) and domain size (192 m × 192 m × 60 m) used in this LES, we demonstrate that the LES is capable of resolving the most important characteristics of the turbulent flow within and above a forest canopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001108411184
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  • 6
    Electronic Resource
    Electronic Resource
    Turbulent kinetic energy budgets from a large-eddy simulation of airflow above and within a forest canopy (1997)
    Springer
    Boundary layer meteorology 84 (1997), S. 23-43 
    Details
    ISSN: 1573-1472
    Keywords: Turbulent kinetic energy ; Large-eddy simulation ; Canopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The output of a large-eddy simulation was used to study the terms ofthe turbulent kinetic energy (TKE) budget for the air layers above andwithin a forest. The computation created a three-dimensional,time-dependent simulation of the airflow, in which the lowest third ofthe domain was occupied by drag elements and heat sources to representthe forest. Shear production was a principal source of TKE in theupper canopy, diminishing gradually above tree-top height and moresharply with depth in the canopy. The transfer of energy to subgridscales (dissipation) was the main sink in the upper part of the domainbut diminished rapidly with depth in the canopy. Removal ofresolved-scale TKE due to canopy drag was extremely important,occurring primarily in the upper half of the forest where the foliagedensity was large. Turbulent transport showed a loss at the canopytop and a gain within the canopy. These general features have beenfound elsewhere but uncertainty remains concerning the effects ofpressure transport. In the present work, pressure was calculateddirectly, allowing us to compute the pressure diffusion term. Wellabove the canopy, pressure transport was smaller than, and opposite insign to, the turbulent transport term. Near the canopy top andbelow, pressure transport acted in concert with turbulent transport toexport TKE from the region immediately above and within the uppercrown, and to provide turbulent energy for the lower parts of theforest. In combination, the transport terms accounted for over half ofthe TKE loss near the canopy top, and in the lowest two-thirds of thecanopy the transport terms were the dominant source terms in thebudget. Moreover, the pressure transport was the largest source ofturbulent kinetic energy in the lowest levels of the canopy, beingparticularly strong under convective conditions. These resultsindicate that pressure transport is important in the plant canopyturbulent kinetic energy budget, especially in the lowest portion ofthe stand, where it acts as the major driving force for turbulentmotions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000301303543
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  • 7
    Electronic Resource
    Electronic Resource
    Book reviews (1993)
    Springer
    Boundary layer meteorology 66 (1993), S. 201-209 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705466
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  • 8
    Electronic Resource
    Electronic Resource
    Large-Eddy Simulation of Windbreak Flow (1998)
    Springer
    Boundary layer meteorology 87 (1998), S. 275-307 
    Details
    ISSN: 1573-1472
    Keywords: Canopy ; Large-eddy simulation ; Windbreak ; Wind tunnel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A large-eddy simulation has been performed of turbulent flow around multiple windbreaks set within a wheat canopy under neutral stability conditions. The simulation is validated against a wind tunnel data set taken under similar conditions. Velocity profiles and second-order statistics are presented and compared to those found in the wind tunnel. From the numerical simulation, we discuss spatial distributions of instantaneous velocity fields and pressure statistics, which are important and telling features of the flow that are difficult to measure experimentally. We present a discussion of the momentum balance at various locations with respect to the windbreak, and similarly, we introduce the budget of a passive scalar. These discussions show the importance of the terms in each budget equation as they vary upstream and downstream of the windbreak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000945626163
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  • 9
    Electronic Resource
    Electronic Resource
    Two-Point Correlation Analysis Of Neutrally Stratified Flow Within And Above A Forest From Large-Eddy Simulation (2000)
    Springer
    Boundary layer meteorology 94 (2000), S. 423-460 
    Details
    ISSN: 1573-1472
    Keywords: Two-point correlation ; Large-eddy simulation ; Pressure perturbations ; Forest meteorology ; Integral scales
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two-point space-time correlations ofvelocities, a passive scalar and static pressure arecalculated using the resolvable flow fields computedby large-eddy simulation (LES) of neutrally stratifiedflow within and above a sparse forest. Zero-time-lagspatial auto-correlation contours in thestreamwise-vertical cross-section for longitudinal andlateral velocities and for a scalar are tilted fromthe vertical in the downstream direction, as istypical in near-wall sheared flow. On the other hand,auto-correlations of vertical velocity and of staticpressure are vertically coherent. Zero-time-lagspatial auto-correlations in the spanwise-verticalcross-section show no distinct tilt, and those forboth longitudinal and vertical velocities demonstratedistinct negative side lobes in the middle forest andabove, while longitudinal velocity in the subcrowntrunk space is laterally in-phase. Static pressureperturbations appear to be spatially coherent in thespanwise direction at all heights, especially insidethe forest. Near the forest floor, longitudinalvelocity is found to be in-phase with static pressureperturbation and to be closely linked to theinstantaneous streamwise pressure gradient, supportinga previous proposal that longitudinal velocity in thisregion is dominantly modulated by the pressurepatterns associated with the coherent sweep/ejectionevents. Near treetop height, a lack of linkage betweenthe pressure gradient and the local time derivative ofthe longitudinal velocity supports the hypothesis ofadvection dominating turbulent flow. The major phase characteristics of the two-pointcorrelations essentially remained the same from fourLES runs with different domain size and/or gridresolution. A larger LES domain yielded betteragreement with field observations in a real forest onboth the magnitudes of the correlations and thesingle-point integral time scales. A finer gridresolution in the LES led to a faster rate of decreaseof correlation with increasing separation in space ortime, as did the higher frequency fluctuations in theturbulent records from field measurements. Convectivevelocities estimated from the lagged two-pointauto-correlations of the calculated flow fields werecompared with similar calculations from wind-tunnelstudies. At the canopy top, estimates from thecorrelation analyses agree with the translationvelocity estimated from instantaneous snapshots of ascalar microfront using both LES and field data. Thistranslation velocity is somewhat higher than the localmean wind speed. Convective velocities estimated fromlagged correlations increase with height above thecanopy. It is suggested that an appropriate filteringprocedure may be necessary to reduce the effects ofsmall-scale random turbulence, as was reported in astudy over an orchard canopy. The mean longitudinalvelocity near the treetops is found to be moreappropriate than the local mean longitudinal velocityat each height to link single-point integral timescales with directly calculated spatial integralstreamwise length scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002430213742
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  • 10
    Electronic Resource
    Electronic Resource
    Large-eddy simulation of turbulent flow above and within a forest (1992)
    Springer
    Boundary layer meteorology 61 (1992), S. 47-64 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A large-eddy simulation has been performed of an atmospheric surface layer in which the lower third of the domain is occupied by a drag layer and heat sources to represent a forest. Subgridscale processes are treated using second-order closure techniques. Lateral boundaries are periodic, while the upper boundary is a frictionless fixed lid. Mean vertical profiles of wind velocity derived from the output are realistic in their shape and response to forest density. Similarly, vertical profiles of Reynolds stress, turbulent kinetic energy and velocity skewness match observations, at least in a qualitative sense. The limited vertical extent of the domain and the artificial upper boundary, however, cause some departures from measured turbulence profiles in real forests. Instantaneous turbulent velocity and scalar fields are presented which show some of the features obtained by tower instrumentation in the field and in wind tunnels, such as the vertical coherence of vertical velocity and the slope of structures revealed by temperature patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02033994
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