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1.
Comparing mixing-length models of the diabatic wind profile over homogeneous terrain 总被引：1，自引：0，他引：1
Alfredo Peña Sven-Erik Gryning Charlotte Bay Hasager 《Theoretical and Applied Climatology》2010,100(3-4):325-335
Models of the diabatic wind profile over homogeneous terrain for the entire atmospheric boundary layer are developed using mixing-length theory and are compared to wind speed observations up to 300 m at the National Test Station for Wind Turbines at Høvsøre, Denmark. The measurements are performed within a wide range of atmospheric stability conditions, which allows a comparison of the models with the average wind profile computed in seven stability classes, showing a better agreement than compared to the traditional surface-layer wind profile. The wind profile is measured by combining cup anemometer and lidar observations, showing good agreement at the overlapping heights. The height of the boundary layer, a parameter required for the wind profile models, is estimated under neutral and stable conditions using surface-layer turbulence measurements, and under unstable conditions based on the aerosol backscatter profile from ceilometer observations. 相似文献
2.
An analysis tool for the study of wind speed profiles over the water has been developed. The profiles are analysed using a
modified dimensionless wind speed and dimensionless height, assuming that the sea surface roughness can be predicted by Charnock’s
roughness length model. In this form, the roughness dependency on wind speed is extracted and the variations on the wind profile
are due solely to atmospheric stability. The use of the Charnock’s non-dimensional wind profile is illustrated using data
collected from a meteorological mast installed in the Danish North Sea. The best fit with the observed mean non-dimensional
wind profile under neutral atmospheric conditions is found using a value of 1.2 × 10−2 for Charnock’s parameter. The stability correction on the neutral wind profile suggested by the Businger-Dyer relations was
found to perform well over the sea. 相似文献
3.
We present an analysis of data from a nearly 1-year measurement campaign performed at Høvsøre, Denmark, a coastal farmland area where the terrain is flat. Within the easterly sector upstream of the site, the terrain is nearly homogenous. This topography and conditions provide a good basis for the analysis of vertical wind-speed profiles under a wide range of atmospheric stability, turbulence, and forcing conditions. One of the objectives of the campaign was to serve as a benchmark for flow over flat terrain models. The observations consist of combined wind lidar and sonic anemometer measurements at a meteorological mast. The sonic measurements cover the first 100 m and the wind lidar measures above 100 m every 50 m in the vertical. Results of the analysis of observations of the horizontal wind-speed components in the range 10–1200 m and surface turbulence fluxes are illustrated in detail, combined with forcing conditions derived from mesoscale model simulations. Ten different cases are presented. The observed wind profiles approach well the simulated gradient and geostrophic winds close to the simulated boundary-layer height during both barotropic and baroclinic conditions, respectively, except for a low-level jet case, as expected. The simulated winds are also presented for completeness and show good agreement with the measurements, generally underpredicting the turning of the wind in both barotropic and baroclinic cases. 相似文献
4.
Juan Carlos Bergmann 《Boundary-Layer Meteorology》2006,119(1):171-179
Precision measurements indicate that the stability capping of the neutral planetary boundary layer (PBL) that leads to a reduced
PBL height is caused by the very stable upper part of the PBL, rather than by an overlying inversion. Radiative processes
related to liquid water in boundary-layer clouds seem to play the key role for the formation of the stable upper PBL. The
famous Leipzig Profile – generally considered as an example of a neutral PBL – has been included in Hess’s analysis because
its PBL height is considerably lower than the ca. 3000 m to be expected by numerical models in truly neutral conditions. An
analysis of the original observations reveals that the Leipzig PBL was stable and that it can be consistently treated as a
‘normal’ stable PBL with a height of ca. 700 m. A further finding is that the super-geostrophic PBL wind speed maxima predicted
by almost all models are not observed in near-steady-state conditions. For the ‘ranking’ of analytical models versus numerical
models, the comparisons with measurements show that the analytical models perform comparably well and even partially better
than the numerical models. 相似文献
5.
Measurements and Parametrizations of the Atmospheric Boundary-Layer Height at Dome C,Antarctica 总被引：2，自引：2，他引：0
Ilaria Pietroni Stefania Argentini Igor Petenko Roberto Sozzi 《Boundary-Layer Meteorology》2012,143(1):189-206
An experimental campaign, Study of the Atmospheric Boundary Layer Environmental at Dome C, was held during 2005 at the French-Italian
station of Concordia at Dome C. Ground-based remote sensors, as well as in situ instrumentation, were used during the experimental
campaign. The measurements allowed the direct estimation of the polar atmospheric boundary-layer height and the test of several
parametrizations for the unstable and stable boundary layers. During the months of January and February, weak convection was
observed while, during the polar night, a long-lived stable boundary layer occurred continuously. Under unstable stratification
the mixing-layer height was determined using the sodar backscattered echoes and potential temperature profiles. The two estimations
are highly correlated, with the mixing height ranging between 30 and 350 m. A simple prognostic one-dimensional model was
used to estimate the convective mixing-layer height, with the correlation coefficient between observations and model results
being 0.66. The boundary-layer height under stable conditions was estimated from radiosounding profiles as the height where
the critical Richardson number is reached; values between 10 and 150 m were found. A visual inspection of potential temperature
profiles was also used as further confirmation of the experimental height; the results of the two methods are in good agreement.
Six parametrizations from the literature for the stable boundary-layer height were tested. Only the parametrization that considers
the long-lived stable boundary layer and takes into account the interaction of the stable layer with the free atmosphere is
in agreement with the observations. 相似文献
6.
We describe the results of an experiment focusing on wind speed and momentum fluxes in the atmospheric boundary layer up to
200 m. The measurements were conducted in 1996 at the Cabauw site in the Netherlands. Momentum fluxes are measured using the
K-Gill Propeller Vane. Estimates of the roughness length are derived using various techniques from the wind speed and flux
measurements, and the observed differences are explained by considering the source area of the meteorological parameters.
A clear rough-to-smooth transition is found in the wind speed profiles at Cabauw. The internal boundary layer reaches the
lowest k-vane (20 m) only in the south-west direction where the obstacle-free fetch is about 2 km. The internal boundary layer
is also reflected in the roughness lengths derived from the wind speed profiles. The lower part of the profile (< 40 m) is
not in equilibrium and no reliable roughness analysis can be given. The upper part of the profile can be linked to a large-scale
roughness length. Roughness lengths derived from the horizontal wind speed variance and gustiness have large footprints and
therefore represent a large-scale average roughness. The drag coefficient is more locally determined but still represents
a large-scale roughness length when it is measured above the local internal boundary layer. The roughness length at inhomogeneous
sites can therefore be determined best from drag coefficient measurements just above the local internal boundary layers directly,
or indirectly from horizontal wind speed variance or gustiness. In addition, the momentum and heat fluxes along the tower
are analysed and these show significant variation with height related to stability and possibly surface heterogeneity. It
appears that the dimensionless wind speed gradients scale well with local fluxes for the variety of conditions considered,
including the unstable cases. 相似文献
7.
Measurements of flow over an elongated ridge and its thermal stability dependence: The mean field 总被引：1，自引：0，他引：1
Measurements of mean wind flow and turbulence parameters have been made over Cooper's Ridge, a 115 m high elongated ridge with low surface roughness. This paper describes measurements of the streamwise and vertical variations in the mean field for a variety of atmospheric stability conditions. In near-neutral conditions, the normalised speedup over the ridge compares well with measurements from Askervein (Mickleet al., 1988). The near-neutral results are also compared to an analytical flow model based on that of Huntet al. (1988a). Measured streamwise variations show less deceleration at the foot of the hill and slightly more acceleration at the crest of the hill than does the model. In non-neutral conditions, the speedup over the ridge reduces slightly in unstable conditions and increases by up to a factor of two in stable conditions. The model is modified to allow boundary-layer stability to change the upwind wind profile and the depths of the inner and middle layers. Such a modification is shown to describe the observations of speedup well in unstable and weakly stable conditions but to overestimate the speedup in moderate to strongly stable conditions. This disagreement can be traced to the model's overestimation of the upstream scaling velocity at the height of the middle layer through its use of a stable wind profile form which has greater shear than that of the observed profiles, in possible combination with the three-dimensionality of the ridge which would allow enhanced flow around, rather than over, the feature in more stable conditions. 相似文献
8.
The mean flow profile within and above a tall canopy is well known to violate the standard boundary-layer flux–gradient relationships.
Here we present a theory for the flow profile that is comprised of a canopy model coupled to a modified surface-layer model.
The coupling between the two components and the modifications to the surface-layer profiles are formulated through the mixing
layer analogy for the flow at a canopy top. This analogy provides an additional length scale—the vorticity thickness—upon
which the flow just above the canopy, within the so-called roughness sublayer, depends. A natural form for the vertical profiles
within the roughness sublayer follows that overcomes problems with many earlier forms in the literature. Predictions of the
mean flow profiles are shown to match observations over a range of canopy types and stabilities.
The unified theory predicts that key parameters, such as the displacement height and roughness length, have a significant
dependence on the boundary-layer stability. Assuming one of these parameters a priori leads to the incorrect variation with stability of the others and incorrect predictions of the mean wind speed profile. The
roughness sublayer has a greater impact on the mean wind speed in stable than unstable conditions. The presence of a roughness
sublayer also allows the surface to exert a greater drag on the boundary layer for an equivalent value of the near-surface
wind speed than would otherwise occur. This characteristic would alter predictions of the evolution of the boundary layer
and surface states if included within numerical weather prediction models. 相似文献
9.
An estimate of roughness length is required by some atmospheric models and is also used in the logarithmic profile to determine the increase of wind speed with height under neutral conditions. The choice of technique for determining roughness lengths is generally constrained by the available input data. Here, we compare sets of roughness lengths derived by different methods for the same site and evaluate their impact on the prediction of the vertical wind speed profile.Wind speed and direction data have been collected at four heights over a three-year period at the North Norfolk Wind Monitoring Site. Wind speed profiles were used to generate sector roughness lengths based on the logarithmic profile formula. This is the only direct way of determining roughness lengths. The simplest and cheapest method is to use maps with published tables giving roughness length estimates for different terrain types. Alternatively Wieringa (1976, 1986) and Beljaars (1987) give formulae for determining roughness lengths from wind speed gusts or standard deviations.The four sets of estimated roughness lengths vary considerably. They were used to estimate 34 m wind speeds from 12.7 m observations. The profile-derived roughnesses are used simply as a check on the prediction of the wind speed profiles. The terrain-derived roughness lengths give reasonable results. Gust-derived and standard deviation roughnesses both predict wind speeds which are lower than the observed ones. The error is greater in the case of standard deviation roughnesses. If stability corrections are applied in the prediction of the vertical wind speed profile, the results are considerably improved. 相似文献
10.
F.E. Hewer 《Boundary-Layer Meteorology》1998,87(3):381-408
Non-linear model simulations of atmospheric boundary-layer flow over the hill called Blashaval have been compared with observations and linear model predictions. Previous studies have shown that linear models can give good predictions of wind speed at the summit and on the upwind slopes of Blashaval. The non-linear model provided wind speed predictions of similar accuracy when compared with the mean observed values at these locations.The published experimental data showed that on the lee-slope the wind speeds at 8m were reduced to approximately 10% of their upstream value at the same height. This was associated with an 180° change in wind direction compared with the upstream flow, suggesting that flow separation had occurred. The non-linear model predictions of lee-slope wind speed, when used with high-resolution topography data, were significantly better than linear model predictions. However, the non-linear model predicted lee-slope wind speeds that were still stronger than observed. The non-linear model simulated flow separation more readily with a 1 1/2-order turbulence closure than with a first-order, mixing-length closure. The configuration of the non-linear model that gave best agreement with observations predicted an 8m lee-slope wind speed that was around 50% of the upstream value. 相似文献
11.
Long-Term Mean Wind Profiles Based on Similarity Theory 总被引：1，自引：1，他引：0
We provide general forms for long-term mean wind profiles from similarity-based wind profiles, beginning with a probabilistic
adaptation of Monin–Obukhov similarity theory. We develop an analytical formulation for the stability distributions prevailing
in the atmospheric surface layer, which in turn facilitates the derivation of a long-term mean wind profile based on Monin–Obukhov
similarity theory. The modelled stability distributions exhibit good agreement with measurements from sites having different
local conditions. The long-term wind profile formulation is further extended to include the influence of the depth of the
atmospheric boundary layer (h), which becomes relevant for heights above h/3, and the resultant long-term ‘tall’ profile form also matches observations. 相似文献
12.
In this paper, the attractors of turbulent flows in phase space are reconstructed by the time delay technique using observed data of atmospheric boundary-layer turbulence, which include high resolution temperature, humidity andthree-dimensional wind speed measurements in Gansu province and Beijing, China. The correlation dimensions and largest Lyapunov exponents have been computed. The results indicate that all the largest Lyapunov exponents in different conditions of time, site and atmospheric stability are greater than zero. This means that the atmospheric boundary-layer turbulence system is really chaotic and has appropriate low-dimensional strange attractors whose dimension numbers range from 3 to 7 and vary with different variables (dynamical variables or non-dynamical variables) and atmospheric stability. Turbulent kinetic energy is first applied to reconstruct the attractor of turbulence, and is found to be feasible. 相似文献
13.
Guillermo J. Berri Jorgelina S. Galli Nuin Laura Sraibman German Bertossa 《Boundary-Layer Meteorology》2012,142(2):329-337
Low-level climatological wind fields over the La Plata River region of South America are synthesized with a dry, hydrostatic
mesoscale boundary-layer numerical model. The model is forced at the upper boundary with the 1200 UTC local radiosonde observations
and at the lower boundary with a land-river differential heating function defined from the daily meteorological observations
of the region. The climatological wind field is defined as the mean value of a series of individual daily forecasts, employing
two methods. The simplified method considers a 192-member ensemble (16 wind directions and 12 wind-speed classes at the upper
boundary). Each member has a probability of occurrence that is determined from the 1959–1984 observations; the daily method
uses a total of 3,248 days with available data during the same period. In both methods each realization is a daily forecast
from which the mean wind distributions at 0300, 0900, 1500 and 2100 local standard time are calculated and compared to the
observations of five meteorological stations in the region. The validation of the climatological wind fields for both methods
is evaluated by means of the root-mean-square error of the wind-direction frequency distribution and mean wind speed by wind
sector. The results obtained with the two methods are similar, and the errors in wind speed are always smaller than those
in wind direction. The combined errors of wind direction and wind speed show that the ensemble method is outperformed by the
daily method, on average by meteorological station in only one out of five of them, and on average by the time of the day
in only one out of 4 h. The conclusion of the study is that the ensemble method is an appropriate methodology for determining
high resolution, low-level climatological wind fields, with the boundary-layer model applied to a region with a strong diurnal
cycle of surface thermal contrast. The proposed methodology is of particular utility for synthesizing wind fields over regions
with limited meteorological observations, since the 192-member matrix can be easily defined with few observing points, as
well as in the case of relatively incomplete records. 相似文献
14.
Measurements of the small-, intermediate-, and large-ion concentrations and the air–earth current density along with simultaneous measurements of the concentration and size distribution of aerosol particles in the size ranges 4.4–163 nm and 0.5–20 μm diameter are reported for a drifting snow period after the occurrence of a blizzard at a coastal station, Maitri, Antarctica. Ion concentrations of all categories and the air–earth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 ms− 1. The rate of decrease is the highest for large ions, lowest for small ions and in-between the two for intermediate ions. Total aerosol number concentration decreases in the 4.4–163 nm size range but increases in the 0.5–20 μm size range with wind speed. The size distribution of the nanometer particles shows a dominant maximum at ~ 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, larger particles show a maximum at ~ 0.7 μm diameter but the height of the maximum increases with increasing wind speed. The results are explained in terms of scavenging of atmospheric ions and aerosols by the drifting snow particles. 相似文献
15.
16.
Characteristics and Numerical Simulations of Extremely Large Atmospheric Boundary-layer Heights over an Arid Region in North-west China 总被引：3，自引：0，他引：3
Over arid regions in north-west China, the atmospheric boundary layer can be extremely high during daytime in late spring
and summer. For instance, the depth of the observed convective boundary layer can exceed 3,000 m or even be up to 4,000 m
at some stations. In order to characterize the atmospheric boundary-layer (ABL) conditions and to understand the mechanisms
that produce such an extreme boundary-layer height, an advanced research version of the community weather research and forecasting
numerical model (WRF) is employed to simulate observed extreme boundary-layer heights in May 2000. The ability of the WRF
model in simulating the atmospheric boundary layer over arid areas is evaluated. Several key parameters that contribute to
the extremely deep boundary layer are identified through sensitivity experiments, and it is found that the WRF model is able
to capture characteristics of the observed deep atmospheric boundary layer. Results demonstrate the influence of soil moisture
and surface albedo on the simulation of the extremely deep boundary layer. In addition, the choice of land-surface model and
forecast lead times also plays a role in the accurate numerical simulation of the ABL height. 相似文献
17.
Acoustic sounder measurements of the stable boundary-layer height taken during the EPRI Plume Model Validation and Development
Project experiment are examined. Comparison of simultaneous measurements by two sodars located 15 km apart shows good agreement.
Several widely used diagnostic formulas for estimation of the boundary-layer height, based on wind speed and surface-layer
parameters, such as friction velocity and Monin-Obukhov length, are tested against the sodar data. Of these, best performance
is found using a simple linear relationship with friction velocity or, alternatively, wind speed at 10 m height. No evidence
is found to support the more often used Zilitinkevich (1972) formula. Tests using selected data from the Cabauw site in the
Netherlands confirm the results found on the basis of EPRI data. 相似文献
18.
Characteristics of the Drag Coefficient in the Roughness Sublayer over a Complex Urban Surface 总被引：2，自引：1，他引：1
The statistics of momentum exchange in the urban roughness sublayer are investigated. The analysis focuses on the characteristics of the dimensionless friction velocity, \({u_{*}}/U\) , which is defined as the square root of the drag coefficient. The turbulence observations were made at a height of 47 m above the ground on the 325-m meteorological tower, which is located in a very inhomogeneous urban area in Beijing. Under neutral conditions, the dependence of the drag coefficient on wind speed varies with wind direction. When the airflow is from the area of densely built-up buildings, the drag coefficient does not vary with wind speed, while when the airflow is from the area covered by vegetation, the drag coefficient appears to decrease with increasing wind speed. Also, the drag coefficient does not vary monotonically with the atmospheric stability. Both increasing stability and increasing instability lead to the decrease of the drag coefficient, implying that the roughness length and zero-plane displacement may vary in urban areas. 相似文献
19.
Aircraft turbulence data from the Autonomous Ocean Sampling Network project were analyzed and compared to the Coupled Ocean–Atmosphere
Response Experiment (COARE) bulk parametrization of turbulent fluxes in an ocean area near the coast of California characterized
by complex atmospheric flow. Turbulent fluxes measured at about 35 m above the sea surface using the eddy-correlation method
were lower than bulk estimates under unstable and stable atmospheric stratification for all but light winds. Neutral turbulent
transfer coefficients were used in this comparison because they remove the effects of mean atmospheric conditions and atmospheric
stability. Spectral analysis suggested that kilometre-scale longitudinal rolls affect significantly turbulence measurements
even near the sea surface, depending on sampling direction. Cross-wind sampling tended to capture all the available turbulent
energy. Vertical soundings showed low boundary-layer depths and high flux divergence near the sea surface in the case of sensible
heat flux but minimal flux divergence for the momentum flux. Cross-wind sampling and flux divergence were found to explain
most of the observed discrepancies between the measured and bulk flux estimates. At low wind speeds the drag coefficient determined
with eddy correlation and an inertial dissipation method after corrections were applied still showed high values compared
to bulk estimates. This discrepancy correlated with the dominance of sea swell, which was a usually observed condition under
low wind speeds. Under stable atmospheric conditions measured sensible heat fluxes, which usually have low values over the
ocean, were possibly affected by measurement errors and deviated significantly from bulk estimates. 相似文献
20.
Hiroshi Ishida 《Boundary-Layer Meteorology》1989,47(1-4):71-84
Based on the data from an array of buoys during the JASIN-1978 field experiment made in an area northwest of Scotland, power spectra of surface wind speed and air temperature over the ocean in the mesoscale frequency range were studied. The averaged composite spectrum of wind speed for the whole period shows the existence of a spectral gap in the frequency range from 10–4 to 5 × 10–3 Hz. However, significant peaks in this range are often seen in particular spectra under certain weather conditions. Mesoscale spectral peaks of wind speed occur in 14 segments of the data record, approximately 10% of the total duration of the observations. In 4 of these segments, the mesoscale spectral peaks of both wind speed and air temperature occurred simultaneously. Several wave patterns of mesoscale atmospheric disturbances when mesoscale spectral peaks were seen are derived from phase differences between buoys. Significant mesoscale peaks in spectra appear in relatively strong winds and unstable or near-neutral atmospheric conditions, and none in stable atmospheric conditions. A criterion of wind speed and atmospheric stability is found for the mesoscale spectral peak appearance. 相似文献