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1.
Turbulence statistics were measured in a natural black-spruce forest canopy in southeastern Manitoba, Canada. Sonic anemometers were used to measure time series of vertical wind velocity (w), and cup anemometers to measure horizontal wind speed (s), above the canopy and at seven different heights within the canopy. Vertical profiles were measured during 25 runs on eight different days when conditions above the canopy were near-neutral.Profiles of s and of the standard deviation ( w ) of w show relatively little scatter and suggest that, for this canopy and these stability conditions, profiles can be predicted from simple measurements made above the canopy. Within the canopy, a negative skewness and a high kurtosis of the w-frequency distributions indicate asymmetry and the persistence of large, high-velocity eddies. The Eulerian time scale is only a weak function of height within the canopy.Although w-power spectra above the canopy are similar to those in the free atmosphere, we did not observe an extensive inertial subrange in the spectra within the canopy. Also, a second peak is present that is especially prominent near the ground. The lack of the inertial subrange is likely caused by the presence of sources and sinks for turbulent kinetic energy within our canopy. The secondary spectral peak is probably generated by wake turbulence caused by form drag on the wide, horizontal spruce branches.  相似文献   

2.
Atmospheric turbulence was measured within a black spruce forest, a jack pine forest, and a trembling aspen forest, located in southeastern Manitoba, Canada. Drag coefficients (C d ) varied little with height within the pine and aspen canopies, but showed some height dependence within the dense spruce canopy. A constant C d of 0.15, with the measured momentum flux and velocity profiles, gave good estimates of leaf-area-index (LAI) profiles for the pine and aspen canopies, but underestimated LAI for the spruce canopy.Velocity spectra were scaled using the Eulerian integral time scales and showed a substantial inertial subrange above the canopies. In the bottom part of the canopies, the streamwise and cross-stream spectra showed rapid energy loss whereas the vertical spectra showed an apparent energy gain, in the region where the inertial subrange is expected. The temperature spectra showed an inertial subrange with the expected -2/3 slope at all heights. Cospectra of momentum and heat flux had slopes of about -1 in much of the inertial subrange. Possible mechanisms to explain some of the spectral features are discussed.  相似文献   

3.
Source/sink distributions of heat, water vapour andCO2 within a rice canopy were inferred using aninverse Lagrangian dispersion analysis and measuredmean profiles of temperature, specific humidity andCO2 mixing ratio. Monin–Obukhov similarity theorywas used to account for the effects of atmosphericstability on w(z), the standard deviation ofvertical velocity and L(z), the Lagrangian timescale of the turbulence. Classical surface layer scaling was applied in the inertial sublayer (z > zruf)using the similarity parameter = (z - d)/L, where z is height above ground, d is the zero plane displacementheight for momentum, L is the Obukhov length,and zruf 2.3hc, where hc iscanopy height. A single length scale hc, was usedfor the stability parameter 3 = hc/L in the height range 0.25 < z/hc < 2.5. This choice is justified by mixing layer theory, which shows that within the roughness sublayer there is one dominant turbulence length scaledetermined by the degree of inflection in the windprofile at the canopy top. In the absence of theoretical or experimental evidence for guidance,standard Monin–Obukhov similarity functions, with = hc/L, were used to calculate the stabilitydependence of w(z) and L(z) in the roughness sublayer. For z/hc < 0.25 the turbulence length and time scales are influenced by the presence of the lowersurface, and stability effects are minimal. With theseassumptions there was excellent agreement between eddycovariance flux measurements and deductions from theinverse Lagrangian analysis. Stability correctionswere particularly necessary for night time fluxes whenthe atmosphere was stably stratified.The inverse Lagrangian analysis provides a useful toolfor testing and refining multilayer canopy models usedto predict radiation absorption, energy partitioningand CO2 exchanges within the canopy and at thesoil surface. Comparison of model predictions withsource strengths deduced from the inverse analysisgave good results. Observed discrepancies may be dueto incorrect specification of the turbulent timescales and vertical velocity fluctuations close to theground. Further investigation of turbulencecharacteristics within plant canopies is required toresolve these issues.  相似文献   

4.
Turbulence measurements above a pine forest   总被引：1，自引：0，他引：1  
Eddy fluxes of momentum, sensible and latent heat, and turbulence spectra measured over the Thetford Forest during 10 days in the Spring of 1973 are described. The measured total heat flux (H + E) for 122 20-min periods agreed closely on average with independent estimates from an energy balance method. There was evidence that the energy balance data gave small systematic overestimates of available energy during the hours before noon, compensated by slight underestimates for the remainder of the day. A comparison of measured wind speeds and friction velocities in neutral stability confirmed the validity of the aerodynamic method for estimating momentum fluxes at heights of a few roughness lengths above the canopy. In stable conditions the log-linear wind profileU = (u */k)(ln ((z -d)/z o) + (z -d -z o)/L) with = 3.4 ± 0.4 provided a good fit to the data. Spectra in unstable conditions were generally more sharply peaked than those measured by other workers over smoother terrain: differences were less marked in the case of vertical velocity in stable conditions. Temperature spectra in these stable conditions showed high energy at relatively low wavenumbers, andwT cospectra showed a cospectral gap; both of these results were associated with an intermittent sawtooth structure in the temperature fluctuations.Now at the Meteorological Office, Bracknell  相似文献   

5.
An analogy has been established between a plane mixing layer and the atmospheric flow near the top of a vegetation canopy. It is based on a common feature, a strong inflection in the mean velocity profile, responsible for hydrodynamical instabilities that set the pattern for the coherent eddies and determine the turbulence length scales. In an earlier study, this analogy was tested using a small data set from thirteen experiments, all in near-neutral conditions. It provided a good prediction of the streamwise spacing w of the dominant canopy eddies (evaluated from time series of vertical velocity) that appears to depend on a shear length scale Ls = U(h)/U'(h), where h is canopy height, U is mean velocity and U' the vertical gradient dU/dz. The present analysis utilizes an extensive data set of approximately 700 thirty-minute runs, from six experiments on two forest sites and a maize crop, with a large range of stability conditions. w was estimated for each run using the wavelet transform as an objective, automated detection method. First, the variations of w and Ls with atmospheric stability are discussed. Neutral and unstable values exhibit a large scatter whereas in stable conditions both variables decrease with increasing stability. It is subsequently found that w is directly related to Ls, in a way close to the neutral prediction w /h = 8.1Ls/h.The Strouhal number Str = Ls /w is then shown to vary with atmospheric stability, weakly in unstable conditions, more significantly in stable conditions. Altogether these results suggest that, to some extent, the plane mixing-layer analogy can be extended to non-neutral conditions. It is argued that the primary effect of atmospheric stability, at least in stable conditions, is to modify the shear length scale Ls through changes in U(h) and U'(h), which in turn determines the streamwise spacing of the active, coherent motions.  相似文献   

6.
An experiment was conducted to study turbulent transport processes of scalar quantities within and above a rice plant canopy. A sonic anemometer-thermometer and a Lyman- humidiometer were used to measure the turbulent fluxes of sensible and latent heat and related turbulence statistics within a paddy field. The sensible and latent heat fluxes measured at two heights within and above the plant canopy showed that the upper layer of this plant canopy was an active source region and that the source strength of sensible and latent heat depended on the solar radiation and physiology of rice plants. Analysis of joint probability distributions of w and T and of w and q within this plant canopy showed that downdrafts were remarkably efficient for upward transport of sensible and latent heat in the daytime. The vertical fluxes of temperature and humidity variance were also divergent from the upper layer of plant canopies. The power spectra of temperature and humidity within the plant canopy decreased rapidly in the high frequency range, compared with the - 2/3 law relationship of nS(n) vs log n observed above plant canopies.  相似文献   

7.
The friction velocity, the surface heat flux and the height of the Atmospheric Boundary Layer (ABL) are important parameters. In this work, vertical velocity variance ( w 2 ) and wind velocity structure parameter (C v 2 ) profiles estimated by acoustic sounder measurements are used, along with similarity relations, to estimate these parameters in the unstable Atmospheric Boundary Layer and the friction velocity in the stable one. The data were collected by two acoustic sounders with different height range and resolution under various atmospheric conditions (stability) and at two experimental sites in different terrain. The C v 2 profiles are estimated using gate difference of the vertical velocity measurements and the assumption of local isotropy. The vertical velocity data are corrected for the significant effects of noisy measurements and sampling volume averaging on the w 2 and C v 2 estimations using original techniques that are presented in this work. The results of the similarity method using acoustic sounder data are compared against estimates of the corresponding atmospheric parameters obtained from direct measurements. The comparison confirms the ability of the method to provide reasonably accurate estimates of these parameters especially in the middle of the day.  相似文献   

8.
This study investigates the organised motion near the canopy-atmosphere interface of a moderately dense spruce forest in heterogeneous, complex terrain. Wind direction is used to assess differences in topography and surface properties. Observations were obtained at several heights above and within the canopy using sonic anemometers and fast-response gas analysers over the course of several weeks. Analysed variables include the three-dimensional wind vector, the sonic temperature, and the concentration of carbon dioxide. Wavelet analysis was used to extract the organised motion from time series and to derive its temporal scales. Spectral Fourier analysis was deployed to compute power spectra and phase spectra. Profiles of temporal scales of ramp-like coherent structures in the vertical and longitudinal wind components showed a reversed variation with height and were of similar size within the canopy. Temporal scales of scalar fields were comparable to those of the longitudinal wind component suggesting that the lateral scalar transport dominates. The existence of a – 1 power law in the longitudinal power spectra was confirmed for a few cases only, with a majority showing a clear 5/3 decay. The variation of effective scales of organised motion in the longitudinal velocity and temperature were found to vary with atmospheric stability, suggesting that both Kelvin-Helmholtz instabilities and attached eddies dominate the flow with increasing convectional forcing. The canopy mixing-layer analogy was observed to be applicable for ramp-like coherent structures in the vertical wind component for selected wind directions only. Departures from the prediction of m = Λ w L s −1 = 8–10 (where Λ w is the streamwise spacing of coherent structures in the vertical wind w and L s is a canopy shear length scale) were caused by smaller shear length scales associated with large-scale changes in the terrain as well as the vertical structure of the canopy. The occurrence of linear gravity waves was related to a rise in local topography and can therefore be referred to as mountain-type gravity waves. Temporal scales of wave motion and ramp-like coherent structures were observed to be comparable.  相似文献   

9.
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 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.  相似文献   

10.
Wind speed was measured at a height of 1 cm above the ground and at several other heights in and above a canopy of tall fescue grass (Festuca arundinacea) using single hot-wire and triple hot-film anemometers. The plant area density in the canopy was concentrated close to the ground, with 75% of the plant area standing belowz=15 cm, wherez is height above the ground. The frequency distributions of horizontal wind speeds,s, were sharply skewed towards positive values at all measurement heights, but were most highly skewed near the ground where the coefficient of skewness ranged from 1.6 to 2.9. Above mid-canopy height, the frequency distribution ofs was described reasonably well by a Gumbel extreme value distribution. Average wind speed,S, decreased exponentially with depth into the canopy with an exponential scale length of abouth/2.8, whereh is the height of the canopy. Atz=1 cm, the value ofS was about 11% of the surface-layeru *. The standard deviation of the fluctuations of the vertical and horizontal components of the wind speed also decreased exponentially with depth inside the canopy with a scale length of abouth/2.5.Inside the canopy, the Eulerian integral time scales for the vertical ( w ) and horizontal ( u ) components of wind speed were about 0.1 s and 1.0 s, respectively, and were approximately constant with height. Above the canopy, these time scales increased sharply and, atz=2.25h, w and u were approximately 1.0 and 3.0s, respectively. Turbulence length scales in the vertical and downwind directions, u and w ·U, respectively, were approximately 1 cm for heights between 1 to 10 cm above the ground inside the canopy, while atz=2.25h, they were about 55 cm and 277 cm. Relatively quiescent periods (lulls) in the air close to the ground were interrupted frequently by gusts. The frequency of occurrence of gusts appears to be correlated with the value of the local shear near the top of the canopy.  相似文献   

11.
It is shown that for the purpose of trajectory simulation, the vertical velocityw L (t) of a fluid element, which is moving in a system (such as a forest canopy, or the unstably stratified atmospheric surface layer) whose turbulent velocity scale w is height-dependent, must be chosen from a frequency-distribution which is asymmetric aboutw L = 0. If the gradient w /z varies only slowly with height, correct trajectories may be obtained by adding a bias (where L is the length scale) to a fluctuating velocity chosen from a symmetric distribution with variance w 2(z).  相似文献   

12.
To investigate tubulence characteristics and organized motion within and above an urban canopy, field observations were conducted in July 1991 and November 1992 in Sapporo, Japan. The measurement heights were 5.4, 10.3, 18, 35 and 45 m above ground; the canopy height was 7 m. The profiles of u peaked slightly above the canopy, while v and w had nearly uniform profiles. Vertical profiles of Reynolds stress - peaked slightly at 1.5 times the canopy height and decreased slowly with height thereafter. A four-quadrant analysis showed that sweep and ejection motions caused high-velocity fluid from above moves downward toward the surface and low-velocity fluid from below moves upward. An ensemble-averaging technique was used to isolate typical features of the flow and temperature fields. A time-height cross-section of velocity vectors and temperature contours showed details of the flow structures associated with temperature ramps. It has been noted that the organized motions play important roles in the transport of heat near the urban canopy, where the sweep motion causes negative temperature fluctuations and the ejection motion causes positive temperature fluctuations.  相似文献   

13.
The dependence of radiometric surface temperature (s) on view angle and the unclear definition of the aerodynamic temperature, which is the temperature that gives the correct sensible heat flux estimate at a specified roughness length, bring about a challenge in estimating sensible heat flux from s. An analytical-land-atmosphere-radiometer model (ALARM) has been developed to convert s taken at any zenith view angle to a clearly defined equivalent isothermal surface temperature, i, at a defined scalar roughness length. ALARM is an analytical model based on K-theory that links the foliage temperature profile to the radiometric surface temperature and the temperature felt by the turbulent lower atmosphere. ALARM has previously been applied with slightly different values of its parameters to several grassland sites of varying canopy density. Our objective in this study was to apply ALARM to these and to one additional dataset with a single parameterization. When compared to the reference (measured) values of sensible heat flux H, ALARM estimates of H had root mean square errors of about 35 W m-2. These results were comparable to those from two other simple canopy models also tested with these datasets.  相似文献   

14.
The profile structure of wind speed and temperature in katabatic flow over a melting glacier is analyzed within the log-linear framework. Similarity between windspeed and temperature profiles is indicated but the log-linear model should be restricted to heights within 1.5 m of the ice. Marked deviation from the model occur at greater heights, probably due to the effects of flux divergence.Unlike results from other stable atmospheres, a decreases with increasing stability. This may arise from the use of the Obukhov length L. When the height H at which the wind speed reaches its maximum value is used instead, does not vary with stability. It has mean values of 4.5 and 4.3 for windspeed and temperature profiles, respectively.  相似文献   

15.
This is the first of a series of three papers describing experiments on the dispersion of trace heat from elevated line and plane sources within a model plant canopy in a wind tunnel. Here we consider the wind field and turbulence structure. The model canopy consisted of bluff elements 60 mm high and 10 mm wide in a diamond array with frontal area index 0.23; streamwise and vertical velocity components were measured with a special three-hot-wire anemometer designed for optimum performance in flows of high turbulence intensity. We found that:
  1. The momentum flux due to spatial correlations between time-averaged streamwise and vertical velocity components (the dispersive flux) was negligible, at heights near and above the top of the canopy.
  2. In the turbulent energy budget, turbulent transport was a major loss (of about one-third of local production) near the top of the canopy, and was the principal gain mechanism lower down. Wake production was greater than shear production throughout the canopy. Pressure transport just above the canopy, inferred by difference, appeared to be a gain in approximate balance with the turbulent transport loss.
  3. In the shear stress budget, wake production was negligible. The role of turbulent transport was equivalent to that in the turbulent energy budget, though smaller.
  4. Velocity spectra above and within the canopy showed the dominance of large eddies occupying much of the boundary layer and moving downstream with a height-independent convection velocity. Within the canopy, much of the vertical but relatively little of the streamwise variance occurred at frequencies characteristic of wake turbulence.
  5. Quadrant analysis of the shear stress showed only a slight excess of sweeps over ejections near the top of the canopy, in contrast with previous studies. This is a result of improved measurement techniques; it suggests some reappraisal of inferences previously drawn from quadrant analysis.
  相似文献   

16.
The heights of the daytime convective boundary layer (CBL), computed by a one-dimensional model for a bare soil surface at a semi-arid station,Anand, during the dry and hot summer month of May 1997, are presented. As input, the model requires surface heat flux, friction velocity and air temperature as functions of time. Temperature data at the one-metre level from a tower and sonic anemometer data at 9.5 m collected during the period 13–17 May 1997 in the Land Surface Processes Experiment (LASPEX-97) are used to compute hourly values of surface heat flux, friction velocity and Obukhov length following the operational method suggested by Holtslag and Van Ulden [J. Climate Appl. Meteorol. 22,517–529 (1983)]. The model has been tested with different values for the potential temperature gradient ( ) above the inversion. The model-estimated CBL heights comparefavourably with observed heights obtained from radiosonde ascents.  相似文献   

17.
An experiment is reported in which heat was released as a passive tracer from an elevated lateral line source within a model plant canopy, with h s = 0.85 h c (h s and h c being the source and canopy heights, respectively). A sensor assembly consisting of three coplanar hot wires and one cold wire was used to measure profiles of mean temperature % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikamaana% aabaGaeqiUdehaaiaacMcaaaa!390C!\[(\overline \theta )\], temperature variance (Σθ 2), vertical and streamwise turbulent heat fluxes, and third moments of wind and temperature fluctuations. Conclusions were:
  1. Despite the very heterogeneous flow within the canopy, the observed dispersive heat flux (due to spatial correlation between time-averaged temperature and vertical velocity) was small. However, there is evidence from the plume centroid (which was lower than h s at the source) of systematic recirculating motions within the canopy.
  2. The ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS% baaSqaaiabeI7aXjaab2gacaqGHbGaaeiEaaqabaGccaGGVaWaa0aa% aeaacqaH4oqCaaWaaSbaaSqaaiaab2gacaqGHbGaaeiEaaqabaaaaa!41DF!\[\sigma _{\theta {\text{max}}} /\overline \theta _{{\text{max}}} \] (of maximum values on vertical profiles) decreased from 1 near the source to an asymptotic value of 0.4 far downstream, in good agreement with previous experimental and theoretical work for concentration fluctuations in the surface layer well above the canopy.
  3. The eddy diffusivity for heat from the line source (K HL ) increased, downstream of the source, to a nearly constant ‘far-field’ vertical profile. Within the canopy, the far-field K HL was an order of magnitude larger than K HP , the equivalent diffusivity for a plane source; well above the canopy, the two were equal. The time scale defined by (far-field K HL )/(vertical velocity variance) was independent of height within the canopy.
  4. Budgets for temperature variance, vertical heat flux and streamwise heat flux are remarkably similar to the equivalent budgets for an elevated line source in the surface layer well above the canopy, except in the lower part of the canopy in the far field, where vertical transport is much more important than in the surface layer.
  5. A random flight simulation of the mean height and depth of the temperature plume was generally in good agreement with experiment. However, details of the temperature and streamwise turbulent heat flux profiles were not correct, suggesting that the model formulation needs to be improved.
  相似文献   

18.
The turbulent heat flux from arctic leads   总被引：2，自引：0，他引：2  
The turbulent transfer of heat from Arctic leads in winter is one of the largest terms in the Arctic heat budget. Results from the AIDJEX Lead Experiment (ALEX) suggest that the sensible component of this turbulent heat flux can be predicted from bulk quantities. Both the exponential relation N = 0.14R x 0.72 and the linear relation N = 1.6 × 10–3 R x+ 1400 fit our data well. In these, N is the Nusselt number formed with the integrated surface heat flux, and R x is the Reynolds number based on fetch across the lead. Because of the similarity between heat and moisture transfer, these equations also predict the latent heat flux. Over leads in winter, the sensible heat flux is two to four times larger than the latent heat flux.The internal boundary layer (IBL) that develops when cold air encounters the relatively warm lead is most evident in the modified downwind temperature profiles. The height of this boundary layer, , depends on the fetch, x, on the surface roughness of the lead, z 0 and on both downwind and upwind stability. A tentative, empirical model for boundary layer growth is % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaadaWcaaqaaiabes% 7aKbqaaiaadQhadaWgaaWcbaGaaGimaaqabaaaaOGaeyypa0JaeqOS% di2aaeWaaeaacqGHsisldaWcaaqaaiaadQhadaWgaaWcbaGaaGimaa% qabaaakeaacaWGmbaaaaGaayjkaiaawMcaamaaCaaaleqabaGaaGim% aiaac6cacaaI4aaaaOWaaeWaaeaadaWcaaqaaiaadIhaaeaacaWG6b% WaaSbaaSqaaiaaicdaaeqaaaaaaOGaayjkaiaawMcaamaaCaaaleqa% baGaaGimaiaac6cacaaI0aaaaaaa!472D!\[\frac{\delta }{{z_0 }} = \beta \left( { - \frac{{z_0 }}{L}} \right)^{0.8} \left( {\frac{x}{{z_0 }}} \right)^{0.4} \] where L is the Obukhov length based on the values of the momentum and sensible heat fluxes at the surface of the lead, and is a constant reflecting upwind stability.Velocity profiles over leads are also affected by the surface nonhomogeneity. Besides being warmer than the upwind ice, the surface of the lead is usually somewhat rougher. The velocity profiles therefore tend to decelerate near the surface, accelerate in the mid-region of the IBL because of the intense mixing driven by the upward heat flux, and rejoin the upwind profiles above the boundary layer. The profiles thus have distinctly different shapes for stable and unstable upwind conditions.  相似文献   

19.
A numerical model of airflow in the lowest 50–100 m of the atmosphere above changes in surface roughness and temperature or heat flux has been developed based on boundary layer approximations, the Businger-Dyer hypotheses for the non-dimensional wind shear and heat flux and a mixing length hypothesis.Results have been obtained for several situations, in particular, airflow with neutral upstream conditions encountering a step change in surface temperature or heat flux with no roughness change. In these cases large increases in shear stress at the outer edge of the internal boundary layer are predicted. The case of unstable upstream flow encountering a step change to zero heat flux is also considered.Two situations that may be encountered near the shores of the Great Lakes are considered.Notation B Businger-Dyer constant (= 16.0) in form for M, H - c p Specific heat at constant pressure - g Acceleration due to gravity - H Upward vertical heat flux - H 0 , H 1 Surface heat fluxes for x < 0, x 0 - k von Kármán's constant ( = 0.4) - l Mixing length - L Monin-Obukhov length - L 0 Upstream value of L - m Ratio of roughness lengths (= z 1/z 0) - RL * Non-dimensional parameter, see Equations (20, 22 and 24) - RL 1 * Same as RL * but with z 1 scaling (= mRL *) - T Scaled temperature - T 0 (z) Upstream temperature profile - u 0, u 1(x) Surface friction velocities for x < 0, x 0 - U, W Horizontal and vertical mean velocities - U 0 (z) Upstream velocity profile - x, z Horizontal and vertical coordinates - z i Local roughness length  相似文献   

20.
Surface renewal analysis for sensible and latent heat flux density   总被引：1，自引：1，他引：0  
High frequency temperature measurements were recorded at five heights and surface renewal (SR) analysis was used to estimate sensible heat flux density (H) over 0.1 m tall grass. Traces of the temperature data showed ramp-like structures, and the mean amplitude and duration of these ramps were used to calculate H using structure functions. Data were compared with H values measured with a sonic anemometer. Latent heat flux density (E) was calculated using an energy balance and the results were compared with E computed from the sonic anemometer data. SR analysis provided good estimates of H for data recorded at all heights but the canopy top and at the highest measurement level, which was above the fully adjusted boundary layer.  相似文献   

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