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  • 1
    Electronic Resource
    Electronic Resource
    Leaf Response to Water Deficits in Soybeans (1978)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 42 (1978), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Soybeans [Glycine max (L.) Merrill cv. Wayne] plants were subjected to an extended drying cycle in the field to investigate the leaf sensitivity to water deficits. Soybeans in irrigated plots were superior to those in non-irrigated plots in the average size and number of leaflets per plant. Apparent differences in the leaf area distributions in the canopy seemed to be mediated by moisture stress effects associated with leaf senescence and light penetration in the lower depths of the canopy. A major decrease in leaf enlargement occurred near a leaf-water potential of -8 bars, and at - 12 bars, the growth was completely halted. Similar decreases were observed at a stomatal conductance of 0.4 cm/s and at 0.2 cm/s no enlargement was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1978.tb01553.x
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  • 2
    Electronic Resource
    Electronic Resource
    Averaging procedures for flow within vegetation canopies (1982)
    Springer
    Boundary layer meteorology 22 (1982), S. 79-90 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Most one-dimensional models of flow within vegetation canopies are based on horizontally averaged flow variables. This paper formalizes the horizontal averaging operation. Two averaging schemes are considered: pure horizontal averaging at a single instant, and time averaging followed by horizontal averaging. These schemes produce different forms for the mean and turbulent kinetic energy balances, and especially for the ‘wake production’ term describing the transfer of energy from large-scale motion to wake turbulence by form drag. The differences are primarily due to the appearance, in the covariances produced by the second scheme, of dispersive components arising from the spatial correlation of time-averaged flow variables. The two schemes are shown to coincide if these dispersive fluxes vanish.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00128057
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  • 3
    Electronic Resource
    Electronic Resource
    Retrieval of turbulent pressure fluctuations at the ground surface beneath a forest (1990)
    Springer
    Boundary layer meteorology 50 (1990), S. 319-338 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The relationship between surface pressure fluctuations and the velocity field associated with turbulent coherent structures is examined for flow within and above a deciduous forest. Measurements were taken with tower-mounted sonic anemometer/thermometers at six heights, Lyman-alpha humidiometers at three heights, and a pressure sensor at the forest floor. We find a strong, near-linear relationship between the mean square turbulent velocity and the standard deviation of the high-pass-filtered pressure fluctuations. Lagged cross-correlations between vertical velocity fluctuations and those of pressure show maximum correlations of ± 0.5 but with a phase offset. Examination of surface pressure during the passage of coherent structures, which are characterized by a transition from ejection to sweep, reveals a period of overpressure about 20 s in duration roughly centered on the time of passage of the scalar microfront at the top of the canopy. Pressure patterns associated with coherent structures appear to be largely responsible for the form of the correlations stated above. Pressure patterns calculated from an integrated Poisson equation, using observed velocity and temperature signals during coherent structures, match the main features of the observed pressure. Retrieval of the pressure fluctuations in this manner reveals that the mean wind shear/turbulence interaction term is dominant, but that important contributions arise from two other terms in the equation. Buoyancy effects are negligible. We show that the surface pressure signal is mainly created by the velocity field near the top of the forest, and present evidence to suggest that features of the sub-crown air movement result directly from this pressure field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120528
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of buoyancy on third-order turbulent velocity statistics within a deciduous forest (1991)
    Springer
    Boundary layer meteorology 55 (1991), S. 109-123 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The influence of atmospheric stability on the behaviour of the third moment of flow velocities observed inside a deciduous forest canopy is examined. Results suggest that buoyancy plays a dominant role in dictating the magnitude of gusts observed inside tall vegetation. Furthermore, an examination of the turbulence recorded throughout leaf fall inside the same forest indicates that larger velocity skewnesses are observed inside a canopy in full leaf than inside a sparse canopy. The behaviour of the measured terms in the non-dimensionalized rate equation of the third moment of canopy flow velocities is also examined. Turbulent diffusion and turbulence gradient interaction terms are largest in stable conditions in the upper canopy layer while these are most important in unstable conditions in the lower canopy layer. In all stability regimes, the turbulent diffusion term is the main source of skewness. The turbulence gradient interaction term, the residual and buoyant production terms all contribute to destroy skewness in stable conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119329
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  • 5
    Electronic Resource
    Electronic Resource
    Evidence of pressure-forced turbulent flow in a forest (1992)
    Springer
    Boundary layer meteorology 58 (1992), S. 273-288 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Lagged cross-correlation analyses between streamwise velocity at several heights within and above a forest, and between streamwise velocity and surface pressure, provide evidence that turbulence in the sub-crown region of the forest is to a large extent driven by pressure perturbations. The analyses support earlier results based on examination of coherent structures observed in the same forest. The phase of the streamwise velocity signal exhibits an increasing delay with decreasing height, indicative of a downwind tilted structure, until the upper region of the forest is reached, at which point the effect is reversed. It is suggested that positive pressure perturbations ahead of advancing microfronts induce streamwise accelerations in the trunk space. This link between the pressure pattern and the wind field explains why velocity spectra in the trunk space are depleted in the higher frequencies, relative to levels above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02033828
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  • 6
    Electronic Resource
    Electronic Resource
    Conditional analysis of temperature and humidity microfronts and ejection/sweep motions within and above a deciduous forest (1992)
    Springer
    Boundary layer meteorology 59 (1992), S. 35-57 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A conditional sampling technique using a multilevel scheme was applied to the detection of temperature and humidity microfronts and organized ejection/sweep motions under different atmospheric stabilities. Data were obtained with seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers within and above a deciduous forest. Both temperature and humidity microfronts were identified in unstable cases, but only humidity microfronts could be detected under neutral conditions. Inverted temperature ramps occurred under slightly stable conditions. Occasionally, wave-like patterns appeared within the canopy, seemingly coupled with inverse ramps occurring above the forest. The frequency of occurrence of scalar microfronts appears to have no clear dependence on atmospheric stability, and averages 74–84 s per cycle with a mode of about 50 s per cycle. However, the strength of ejections and sweeps, shown by the vertical velocity averaged within structures, was reduced by increasing atmospheric stability. Structures identified under different stabilities show many similarities in their patterns of scalar ramps, and associated velocity and surface pressure. Profiles of short-term averaged longitudinal velocity at different times during the microfront passage show that the air within the canopy was retarded and an intensified shear above the canopy occurred prior to the passage of the microfront. Results from the present conditional analysis strongly suggest an important role of shear instability in the formation of canopy coherent structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120685
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of organized structure in turbulent flow within and above a forest canopy (1989)
    Springer
    Boundary layer meteorology 47 (1989), S. 349-377 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Ramp patterns of temperature and humidity occur coherently at several levels within and above a deciduous forest as shown by data gathered with up to seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers at an experimental site in Ontario, Canada. The ramps appear most clearly in the middle and upper portion of the forest. Time/height cross-sections of scalar contours and velocity vectors, developed from both single events and ensemble averages of several events, portray details of the flow structures associated with the scalar ramps. Near the top of the forest they are composed of a weak ejecting motion transporting warm and/or moist air out of the forest followed by strong sweeps of cool and/or dry air penetrating into the canopy. The sweep is separated from the ejecting air by a sharp scalar microfront. At approximately twice the height of the forest, ejections and sweeps are of about equal strength. In the middle and upper parts of the canopy, sweeps conduct a large proportion of the overall transfer between the forest and the lower atmosphere, with a lesser contribution from ejections. Ejections become equally important aloft. During one 30-min run, identified structures were responsible for more than 75% of the total fluxes of heat and momentum at mid-canopy height. Near the canopy top, the transition from ejection of slow moving fluid to sweep bringing fast moving air from above is very rapid but, at both higher and lower levels, brief periods of upward momentum transfer occur at or immediately before the microfront.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122339
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  • 8
    Electronic Resource
    Electronic Resource
    Joint probability analysis of momentum and heat fluxes at a deciduous forest (1990)
    Springer
    Boundary layer meteorology 52 (1990), S. 283-300 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Turbulent transport processes for momentum and scalar quantities are examined by a joint probability distribution analysis using data observed within and above a deciduous forest. Characteristics of transport processes in the frequency domain were also analyzed using Tukey's procedure. The results confirm that sweep phenomena prevail within and at the top of a tall plant canopy and that downdrafts are more effective for vertical transport of momentum and scalar quantities. On the other hand, updrafts become more efficient for vertical transport in the daytime at levels about twice treetop height. The results show that within the forest, the sweep phenomenon prevails over a wide frequency range, while above the forest, prevalence of the ejection phenomenon is limited to low frequencies. It is again noted that the plant canopy plays an important role in the sweep-ejection cycle as well as in turbulent transport processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122091
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of foliar density and thermal stability on profiles of Reynolds stress and turbulence intensity in a deciduous forest (1988)
    Springer
    Boundary layer meteorology 45 (1988), S. 391-409 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations were made of turbulence in an extensive deciduous forest on level terrain using a vertical array of seven three-dimensional sonic anemometer/thermometers within and above the canopy. Data were collected through the period of leaf fall and over a range of thermal stabilities. A bulk canopy drag coefficient was nearly independent of the density of the forest but decreased greatly with the onset of nocturnal stability. The depth of penetration of momentum into the forest increased with leaf fall but, again, was greatly curtailed by stable conditions. Turbulent velocities decreased with increasing depth in the forest but relative turbulence intensities increased to mid-canopy levels. Leaf density influenced turbulence levels but not as strongly as did thermal stability. Thermal effects were adequately described by the single parameter h/L, where h is the canopy height and L is the Monin-Obukhov length. The longitudinal and vertical velocity correlation coefficient was larger in magnitude than expected in the upper layers of the forest but decreased to a small value in the lowest layers where the Reynolds stress was small. The ratio Σ w /u *, where u * is the local friction velocity, reflected changes in the uw correlation, becoming smaller than usual in the upper canopy layers. It is believed that these effects result from the intermittent, spatially coherent structures that are responsible for a large fraction of the momentum flux to the forest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00124010
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  • 10
    Electronic Resource
    Electronic Resource
    A miniature three-dimensional anemometer for use within and above plant canopies (1973)
    Springer
    Boundary layer meteorology 3 (1973), S. 359-380 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A miniature anemometer has been designed for the measurement of turbulent transport within canopies. The sensing element utilizes a relatively new concept in hot-film anemometry, in which the angular measurement is derived from the non-uniformity in heat transfer coefficient around the circumference of the cylindrical hot-film. The element is split along its length to form two separate conducting films and the relative magnitudes of the heat convected from each side are used to calculate the elevation angle of the wind. An electromechanical servosystem operated by a second split-film keeps the sensing head facing into the wind. The anemometer measures all three components of velocity over the complete solid angle without octant ambiguity and at velocities as low as 20 cm s−1. It is a research instrument and because of its non-linear response characteristics, data handling is best accomplished by digital computer. The response of the split-film elements extends to high frequencies. The servo-system follows turbulent fluctuations up to approximately 5 Hz and keeps the probe within a few degrees of the wind at all times. In field tests, total wind speed and wind component measurements compared well with more conventional anemometers; eddy-correlation measurements of shear-stress with the split-film anemometer were in good agreement with measurements from a shear stress lysimeter and from a pressure-sphere anemometer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00736186
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