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1.
A. V. Glazunov 《Izvestiya Atmospheric and Oceanic Physics》2006,42(3):282-299
The neutrally stratified boundary layer over a smooth rough surface is consider. The turbulent flow is simulated using a finite-difference eddy-resolving model of the atmospheric boundary layer (ABL). The model includes different turbulence closure schemes and numerical approximations for advection components of the momentum balance equation. We investigate the quality of reproduction of spectral characteristics of the turbulent flow and the model’s capabilities to reproduce the observed profile of mean wind velocity near the rough surface. It is shown that the best result is obtained by coupling a numerical scheme of higher order of accuracy with a mixed closure scheme based on an adaptive estimation of the mixing length for subgrid-scale fluctuations. Here, we are able to reproduce the asymptotics of the fluctuation spectrum of the longitudinal component of wind velocity near the surface and within the boundary layer as well as the logarithmic profile of mean velocity near the surface. 相似文献
2.
We perform the experimental verification of the applicability of the theory of similarity to the wave boundary layer and the
assessment of wave-induced perturbations of the air flow depending on various conditions of stratification of the atmosphere
and the state of the sea. The measurements were carried out from a stationary platform located in the coastal part of the
Black Sea. The experimental procedure is based on the simultaneous measurements of the profile and fluctuations of the wind
speed at 5–6 levels in the 1.3–21-m layer, the elevations of the sea surface, the directions of waves and winds, and the mean
gradients of temperature and humidity of air. The structure of the boundary layer in the region of measurements depends on
the direction of the wind. For weak and moderate onshore winds (< 9 m/sec), the approximate balance is preserved between the
production and dissipation of turbulent energy in the cases of unstable and neutral stratification. On the average, the estimates
of friction velocity according to the profiles are higher than the dissipative estimates by 10% mainly due to the deficiency
of dissipation near the surface. For the offshore wind, the structure of the boundary layer abruptly changes and is determined
not by the local parameters but by strong turbulent eddies formed over the dry land. The intensity of low-frequency turbulent
fluctuations and the gradient of wind velocity near the surface in the coastal zone are 1.5–2 times higher than for the open
sea.
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Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 42–61, May–June, 2007. 相似文献
3.
Using large eddy simulation (LES) incorporating the effect of the horizontal component of the earth’s rotation vector, we
studied the seafloor turbulent boundary layer to investigate the dependence of the boundary layer thickness on the overlying
geostrophic flow orientation. The thickest boundary layer appears for the westward geostrophic flow: it is almost twice that
of the eastward flow. The turbulent disturbances in the boundary layer are elongated slightly leftward relative to the geostrophic
flow. Linear stability analysis for the Ekman’s spiral flow showed that the growth rate is maximum for the westward geostrophic
flow and the unstable roll-like mode appears, which points slightly leftward relative to the geostrophic flow. These properties
correspond to the feature near the bottom of the developed turbulent layer. 相似文献
4.
Using a high-resolution LES numerical model, we calculated the turbulent thermal convection for high ratios of horizontal and vertical sizes of the computational domain (26: 26: 1). The natural analog of the simulated process is a planetary boundary layer (PBL) of the atmosphere growing with height in the background of stably stratified overlying air layers over a horizontally homogeneous heated surface under a weak average wind. We obtained the spectral distributions of variances of fluctuations in potential temperature and velocity components in ranges corresponding to scales from a few tens of meters to a few tens of kilometers. We found energetically significant segments of the spectrum of large-scale fluctuations in the potential temperature for which the power dependences S ～ k ?1/3 and S ～ k ?4/3 are satisfied with good accuracy. We calculated the characteristic spatial scales of horizontal fluctuations in velocity and temperature. We obtained a dependence of these scales on the height of the growing convective PBL. We discuss the characteristic features of large-scale distributions in terms of the self-similarity of the growing boundary layer behavior. 相似文献
5.
The results of model calculations and experimental research of turbulent jet propagation in a stratified environment with
reference to the Sand Island wastewater outfall (Hawaii) are considered. The jet’s emergence and initial dilution were estimated
on the basis of model calculations and experimental data of the stratified environment characteristics in 2003–2004. The reason
for the appearance of the bidirectional quasi-isopycnic structure in the waste and ocean water mixing area was clarified,
and an analysis of the TS index was carried out. The jet’s features as calculated from the model and obtained from measurements with hydrophysical
and hydrooptical instrumentation were found to closely correspond. The effects of the tides and hydrophysical conditions on
the waste water’s turbulent jet characteristics (the jet’s floating-up depth level) have been revealed. The outcomes of the
study corroborate the efficiency of the model as a tool for research of deep outfall turbulent jet propagation in the stratified
environment of coastal water areas. 相似文献
6.
A modified three-parameter model of turbulence for a thermally stratified atmospheric boundary layer (ABL) is presented. The model is based on tensor-invariant parametrizations for the pressure-strain and pressure-temperature correlations that are more complete than the parametrizations used in the Mellor-Yamada model of level 3.0. The turbulent momentum and heat fluxes are calculated with explicit algebraic models obtained with the aid of symbol algebra from the transport equations for momentum and heat fluxes in the approximation of weakly equilibrium turbulence. The turbulent transport of heat and momentum fluxes is assumed to be negligibly small in this approximation. The three-parameter E ? ε ? 2> model of thermally stratified turbulence is employed to obtain closed-form algebraic expressions for the fluxes. A computational test of a 24-h ABL evolution is implemented for an idealized two-dimensional region. Comparison of the computed results with the available observational data and other numerical models shows that the proposed model is able to reproduce both the most important structural features of the turbulence in an urban canopy layer near the urbanized ABL surface and the effect of urban roughness on a global structure of the fields of wind and temperature over a city. The results of the computational test for the new model indicate that the motion of air in the urban canopy layer is strongly influenced by mechanical factors (buildings) and thermal stratification. 相似文献
7.
Theoretical models of the height of the atmospheric boundary layer and turbulent entrainment at its upper boundary 总被引：2，自引：0，他引：2
S. S. Zilitinkevich Yu. I. Troitskaya E. A. Mareev 《Izvestiya Atmospheric and Oceanic Physics》2012,48(1):133-142
The planetary boundary layer (PBL), which directly interacts with the underlying surface, differs significantly in its nature
from the low-turbulent stably stratified free atmosphere. Fluctuations of the Earth’s surface heat balance immediately affect
the PBL and assimilate there owing to the effective mechanism of turbulent heat transfer. In this case the upper boundary
of the PBL plays the role of a cover, preventing the direct penetration of thermal effects and contaminants into an overlying
atmospheric layer. In view of this, air pollution is especially dangerous when associated with shallow PBL. In addition, local
peculiarities of climate change are mainly determined by the PBL height due to the high sensitivity of thin stably stratified
PBLs to the thermal effects. Deep convective PBLs are not very sensitive to weak thermal effects, but they significantly affect
the formation of convective cloudiness and the climate system as a whole by means of the turbulent entrainment of the thermal
energy, humidity, aerosols, and other admixtures through the upper boundary. The PBL height and turbulent entrainment must
be calculated when simulating and forecasting air pollution, abnormal frosts and heat, and other hazardous phenomena. In this
paper we discuss the state-of-the-art knowledge in the area of PBL height simulation and suggest a new model of turbulent
entrainment for convective PBLs. 相似文献
8.
The seasonal variability of sonic layer depth (SLD) in the central Arabian Sea (CAS) (0 to 25°N and 62-66°E) was studied using
the temperature and salinity (T/S) profiles from Argo floats for the years 2002–2006. The atmospheric forcing responsible
for the observed changes was explored using the meteorological data from NCEP/NCAR and Quickscat winds. SLD was obtained from
sound velocity profiles computed from T/S data. Net heat flux and wind forcing regulated SLD in the CAS. Up-welling and down-welling
(Ekman dynamics) associated with the Findlater Jet controlled SLD during the summer monsoon. While in winter monsoon, cooling
and convective mixing regulated SLD in the study region. Weak winds, high insolation and positive net heat flux lead to the
formation of thin, warm and stratified sonic layer during pre and post summer monsoon periods, respectively. 相似文献
9.
Turbulent wall pressure data acquired during tests of a full-scale experimental towed array over a range of tow speeds in straight tows and turns is presented. The experimental towed array contained a linear array of sensors mounted at the fluid–solid interface to measure the spectra of the wall pressure fluctuations due to the cylindrical turbulent boundary layer. The physics are dominated by the growth of a thick, high Reynolds number turbulent boundary layer at arc length Reynolds numbers as high as 9×108. The measured wavenumber-frequency spectra, autospectra, cross-spectral decay and convection velocities are presented. A well-defined convective ridge exists in the wavenumber-frequency spectra obtained during straight tows and turns. Turns give rise to a complicated fluid–structure interaction problem, but do not lead to the separation of the turbulent boundary layer. As the array moves through a turn, flow-induced vibrations of the array are shown to dominate the spectra at low frequencies, with more rapid decay in the measured coherence occurring at higher frequencies. The use of tow speed as a velocity scale is shown to collapse autospectra and convection velocities. 相似文献
10.
The results obtained from both atmospheric and laboratory measurements and from LES data show that, in the stably stratified
flows of the atmospheric boundary layer, turbulent mixing occurs at gradient Richardson numbers Ri
g
that significantly exceed one: the inverse turbulent Prandtl number Pr
t
−1 decreases with an increase in the thermal flow stability. The decreasing trend of the inverse turbulent Ptandtl number is
reproduced in a stably stratified atmospheric boundary layer in agreement with measurement data with the aid of an improved
three-parameter turbulence model. In this model, a modified model that takes into account the effect of stratification in
the expression for the time scale of the scalar field is used for the pressure-scalar correlation. 相似文献
11.
INTROOCCrIOWWiththeimplementationoftimeseriesobservationsspanningseveralsynopticweathersystempassages,theimPOrtanceoftheattnosphericallyforcedpartofestuarinecirculationbecameclearinthe1970s.WeisbetgandSturges(1976)examinedthewindeffectindrivingthenetcirculationintheWestPassageoftheNarragansettBay.Usingvelocitymeasurementsofapproximatelyonemonthduration,theyconcludedthatthelocalwindscoulddominatethegravitationalconvectionindeterminingthenetestuarinecirculationprofileofapartiallymixedestu… 相似文献
12.
The problem of recognition of algal genera based on the remote sensing data requires the analysis of the algae biomass’s distribution.
This study provides the analysis of the algae spatial and temporal variations in the Peter the Great Bay. While 116 algal
genera were observed, only a few genera have dominated. Usually, the dominant genus contributed about 60% of the sample’s
biomass (the minimal value is 20% usually) and 4 dominant genera contributed about 90% of the total phytoplankton biomass.
The effective scattering crosssection of the algae in the samples is very changeable and this feature looks promising for
the recognition problem. It was found that the spatial and temporal variations of the algal biomass are significant, but the
percentage characteristics of a few dominant genera are relatively stable with no significant dependence on a region and a
biomass value. The algae’s composition analysis has demonstrated that the same algal genera are propagated in different parts
of the Bay. For a given region and month, the set of algae dominated that constitutes about 90% of the monthly biomass is
rather small (not more than 10 genera usually). Most of the alga genera (∼75%) do not ever reach a mono domination state (more
than 50% of the sample’s biomass). 相似文献
13.
Both wind turning with height and ageostrophic flow in a stably stratified atmospheric boundary layer are analyzed using a three-parameter turbulence model. For a quasi-steady state of the boundary layer, the cross-isobaric flow is determined only by turbulent stress at the surface in the direction of geostrophic wind. The “operative” prediction models, in which the first-order turbulence closure schemes are used, tend to overestimate the boundary-layer depth and underestimate the angle between the surface and geostrophic winds when compared to “research” models (schemes of high-level turbulence closure). The true value of the angle between the surface and geostrophic winds is significant for the presentation of a large-scale flow. A nocturnal low-level jet is a mesoscale phenomenon reflected in data obtained from measurements in a stably stratified atmospheric boundary layer. It is found that such jets are of great importance in transporting humidity, momentum, and air pollution. In this study, the difference between jet flows over a homogeneous underlying surface and over a spatially localized large-scale aerodynamic roughness is shown. 相似文献
14.
A numerical study of the summertime flow around the Luzon Strait 总被引：3，自引：0，他引：3
Luzon Strait, a wide channel between Taiwan and Luzon islands, connects the northern South China Sea and the Philippine Sea.
The Kuroshio, South China Sea gyre, monsoon and local topography influence circulation in the Luzon Strait area. In addition,
the fact that the South China Sea is a fairly isolated basin accounts for why its water property differs markedly from the
Kuroshio water east of Luzon. This work applies a numerical model to examine the influence of the difference in the vertical
stratification between the South China Sea and Kuroshio waters on the loop current of Kuroshio in the Luzon Strait during
summer. According to model results, the loop current’s strength in the strait reduces as the strongly stratified South China
Sea water is driven northward by the southwest winds. Numerical results also indicate that Kuroshio is separated by a nearly
meridional ridge east of Luzon Strait. The two velocity core structures of Kuroshio can also be observed in eastern Taiwan.
Moreover, the water flowing from the South China Sea contributes primarily to the near shore core of Kuroshio. 相似文献
15.
Turbulent characteristics and current velocity are calculated in the framework of a quasistationary model for a shallow sea,
using the equations for Reynolds stress transport and for the rate of dissipation. The paper shows that the ‘negative viscosity’
effect manifests itself in the near-bottom layer, related to energy transfer from pulse motions of turbulent flow to the mean
ones.
Translated by Vladimir A. Puchkin. 相似文献
16.
D. Myrhaug 《Ocean Engineering》1992,19(4)
The friction velocity associated with the maximum bottom shear stress in neutrally stable tidal planetary boundary layer flow is presented. The directions of the bottom shear stresses for the anticlockwise and clockwise rotating components are also presented. The results are obtained by using similarity theory and are given for flow conditions in the rough, smooth and transitional smooth-to-rough turbulent regime. An approximation for the maximum bottom shear stress by disregarding the rotation of the velocity in the boundary layer as the seabed is approached is also presented. 相似文献
17.
G. T. Csanady 《Journal of Oceanography》1997,53(1):67-80
A “slip law” connects the excess velocity or “slip” of a wind-blown water surface, relative to the motion in the middle of
the mixed layer, to the wind stress, the wind-wave field, and buoyancy flux. An inner layer-outer layer model of the turbulent
shear flow in the mixed layer is appropriate, as for a turbulent boundary layer or Ekman layer over a solid surface, allowing,
however, for turbulent kinetic energy transfer from the air-side via breaking waves, and for Stokes drift. Asymptotic matching
of the velocity distributions in inner and outer portions of the mixed layer yields a slip law of logarithmic form, akin to
the drag law of a turbulent boundary layer. The dominant independent variable is the ratio of water-side roughness length
to mixed layer depth or turbulent Ekman depth. Convection due to surface cooling is also an important influence, reducing
surface slip. Water-side roughness length is a wind-wave property, varying with wind speed similarly to air-side roughness.
Slip velocity is typically 20 times water-side friction velocity or 3% of wind speed, varying within a range of about 2 to
4.5%. A linearized model of turbulent kinetic energy distribution shows much higher values near the surface than in a wall
layer. Nondimensional dissipation peaks at a value of about eight, a short distance below the surface. 相似文献
18.
H.O. Anwar 《Estuarine, Coastal and Shelf Science》1983,17(3):243-260
From mean velocities measured in estuarine flows it has been found that the velocity distributions are log-linear in stratified flows and logarithmic in well-mixed flows. The results of salinity measurements reveal that the mean salinity profiles are geometrically similar and expressible as a power law. The buoyancy parameters, such as the Monin-Obukhov length scale, the gradient and the flux Richardson numbers, are independent of the flow state. The gradient and the flux Richardson numbers are almost equal, indicating the existence of a local equilibrium layer. The non-dimensional parameter describing dissipation rates of turbulent kinetic energy is a constant of 0·2 and 0·3 for stratified and well-mixed flows respectively. In well-mixed flow the drag coefficient varies with time approaching a constant of about 3·2 × 10?3 when the flow is stratified. The shape of the turbulent energy spectra are generally flatter and broader in stratified as compared with those of well-mixed flows. 相似文献
19.
We present the results of experimental investigations of the characteristics of turbulence in the layer of wave-induced mixing.
The data on the fluctuations of velocity, temperature, and conductivity are obtained with the help of a Sigma-1 measuring complex. The computed values of the dissipation rate of turbulent energy are compared with different models proposed
for the subsurface layer. It is shown that the available models fail to guarantee satisfactory agreement of the numerical
results with the experimental data for the layer of active wave action and, in particular, in the presence of swell. This
leads us to the conclusion concerning the necessity of parametrization and assimilation of more complete data on the state
of the sea surface, the structure of currents, and the surface layer of the atmosphere in the models.
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Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 15–28, March–April, 2007. 相似文献
20.
黄东海大气边界层高度时空变化特征 总被引：4，自引：0，他引：4
根据2006-2007年大连、青岛和台州逐日高分辨率L波段二次测风雷达探空资料、地面观测资料以及再分析资料,采用干绝热法和位温梯度法分别计算了各个台站的边界层高度,继而分析了黄东海边界层高度多时间尺度变化规律和空间演变特征.结果表明:(1)用清晨探空资料计算每日边界层高度,干绝热法比位温梯度法更为合理可靠;(2)沿海台站边界层高度有显著季节变化,夏季最低,秋季最高,这有别于陆地边界层普遍存在的夏季高、秋冬季节低的季节变化;(3)通过小波分析,发现边界层高度有显著的2～4 d天气尺度振荡和10～20 d准双周振荡;(4)黄东海上空海洋大气边界层在时间尺度上同样存在着明显的春夏季节低、秋冬季节高的季节变化特征,大部分海区空间上呈现西北低、东南高的分布形态. 相似文献