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1.
S. S. Zilitinkevich 《Boundary-Layer Meteorology》1989,49(1-2):1-5
A logarithmic + polynomial approximation is proposed for the vertical temperature profile in a neutrally or stably stratified planetary boundary layer (PBL) in conditions of quasi-stationarity. Using this approximation with the asymptotic logarithmic + linear law of the Monin-Obukhov similarity theory for the near-surface layer and with the Zilitinkevich formula for the PBL thickness allows one to derive an analytical expression for the function C in the heat transfer law, which permits simple parameterization of the thermal interaction between the atmosphere and the underlying medium in terms of external parameters, such as the geostrophic wind velocity and the temperature difference across the PBL. 相似文献
2.
Summary On the basis of Wu and Blumen's work (1982) on the geostrophic momentum approximation (GMA) in the planetary boundary layer (PBL) and Tan and Wu (1992, 1994) on the Ekman momentum approximation (EMA) in the PBL, some improvements about the eddy exchange coefficientK, the advective inertial force and the lower boundary condition of the PBL are developed in this paper: (1) apply theK which is a gradually varying function of height instead of a constant value in the Ekamn layer, and introduce a surface layer; (2) take the effect of the vertical advective inertial force into account; (3) the solution technique is extended from level terrain to orographically formed terrain. Under the condition of the equilibrium among four forces (the pressure — gradient force, Coriolis force, eddy viscous force and inertial force including horizontal and vertical advective inertial forces), we have obtained the analytical solutions of the distributions of the wind and the vertical velocity. The computation of an individual example shows that: (1) both the wind velocity near surface and the angle between which and the non-viscous wind are more consistent with usual observations than that of Wu and Blumen (1982); (2) comparing with the horizontal advective inertial force, the vertical advective inertial force can not be neglected, when the orography is considered, the effect of the latter is even more important than the former.With 3 Figures 相似文献
3.
By use of the small parameter expansion method, the nonlinear planetary boundary layer (PBL) is studied in this paper. The PBL is divided into the surface layer and the Ekman layer, which is divided into several sublayers. In the surface-layer, the eddy coefficient K is taken as a linear function of height; in the Ekman layer, different constant K values are taken within different sublayers: these values are determined from O'Brien's formula (O'Brien, 1970) approximately. Under the upper and lower boundary conditions and the continuity conditions of the wind velocities and turbulent stresses at each boundary between sublayers, analytical expressions for wind velocity in all sublayers and the vertical velocity at the top of the PBL are obtained. A specific example of steady axisymmetrical circular high and low pressure areas is analysed, and some new conclusions are obtained. The results are in better agreement with reality than previous results. This example also shows that the vertical velocity at the top of the PBL caused by friction approaches zero near the center of a high or low pressure system for this model, but attains its maximum absolute values near the center of the high or low pressure area for Wu's (1984) model. This is due to the fact that in our model, the geostrophic wind speed near the center of this specific vortex approaches zero, which causes the wind shear and the friction effect to be very weak. Therefore the wind distribution in the PBL is very sensitive to the type of eddy coefficient. 相似文献
4.
In this paper, Wu and Blumen’s boundary layer geostrophic momentum approximation model (Wu and Blumen, 1982) is applied to baroclinic and non-neutral PBL, the motion equations for the PBL under the geostrophic momentum approximation are solved, in which the eddy transfer coefficient is a function of the distributions of the wind and temperature. The results are compared with those in barotropic and neutral conditions with the geostrophic momentum approximation. It is found that in the baroclinic condition, the wind distribution has both the characteristics of a steady, homogeneous and baroclinic PBL and those caused by the geostrophic momentum approximation. Those in non-neutral conditions show that they retain the intrinsic characteristics for the wind in non-neutral PBL, at the same time, the effects of the large-scale advection and local variation are also included. We can predict the wind in the non-neutral and baroclinic PBL by use of the geostrophic mo-mentum approximation when the temporal and spatial distributions of the geostrophic wind, as well as the po-tential temperatures and their variation rates at the upper and lower boundary of the PBL are given by large-scale model. Finally, the model is extended to the case over sea surface. 相似文献
5.
An efficient, pianetary boundary layer (PBL) model is developed and validated with empirical data for applications in general circulation models (GCMs). The purpose of this PBL model is to establish the turbulent surface fluxes as a function of the principal external PBL parameters in a numerically efficient way. It consists of a surface layer and a mixed layer matched together with the conditions of constant momentum and heat flux at the interface. An algebraic solution to the mean momentum equations describes the mixed-layer velocity profile and thus determines the surface wind vector. The velocity profile is globally valid by incorporating the effect of variable Coriolis force without becoming singular at the equator. Turbulent diffusion depends on atmospheric stability and is modeled in the surface layer by a drag law and with first-order closure in the mixed layer. Radiative cooling in the stably stratified PBL is considered in a simple manner. The coupled system is solved by an iterative method. In order to preserve the computational efficiency of the large-scale model, the PBL model is implemented into the GISS GCM by means of look-up tables with the bulk PBL Richardson number, PBL depth, neutral drag coefficient, and latitude as independent variables.A validation of the PBL model with observed data in the form of Rossby number similarity theory shows that the internal feedback mechanisms are represented correctly. The model, however, underpredicted the sensible heat-flux. A subsequent correction in the turbulence parameterization yields better agreement with the empirical data. The behavior of the principal internal PBL quantities is presented for a range of thermal stabilities and latitudes. 相似文献
6.
R. A. Brown 《Boundary-Layer Meteorology》1978,14(3):381-396
A two-layer, first-order closure model for the Planetary Boundary Layer (PBL) is developed with the objective of parameterizing the surface stress with respect to the synoptic scale. The model includes stability effects by considering stratification-dependent secondary flow in the outer layer and empirical corrections to the surface layer flow. It shows the compatibility of simple eddy viscosity closure solutions with similarity theory by producing the now well-known Rossby similarity equations. It allows further insight into the Rossby similarity parameters by relating them to a single similarity parameter which is the ratio of the characteristic scales of the PBL and the surface layer.The measured and derived values of the similarity parameters A and B are compared with AIDJEX data and other published values. The variation in these values in stably stratified conditions is predicted and two alternate similarity parameters are calculated, one a constant and the other with a small variation and decreasing influence on the drag coefficient in stable stratification. The result is an empirical resistance law for a geostrophic drag coefficient variation which parameterizes an observed order-of-magnitude change in surface stress with changes in roughness or PBL stratification. This variation is related to similarity parameters characteristic of the region and to measurable changes in the geostrophic departure angle. 相似文献
7.
Mesoscale models using a non-local K-scheme for parameterization of boundary-layer processes require an estimate of the planetary boundary layer (PBL) height z
i
at all times. In this paper, two-dimensional sea-breeze experiments are carried out to evaluate three different formulations for the advective contribution in the z
i
prognostic equation of Deardorff (1974).Poor representation of the thermal internal boundary layer in the sea breeze is obtained when z
i
is advected by the wind at level z
i
. However, significantly better results are produced if the mean PBL wind is used for the advecting velocity, or if z
i
is determined simply by checking for the first sufficiently stable layer above the ground.A Lagrangian particle model is used to demonstrate the effect of each formulation on plume dispersion by the sea breeze. 相似文献
8.
Measurements have been made in both a neutral and a stable boundary layer as part of an investigation of the wakes of wind turbines in an offshore environment, in the EnFlo stratified flow wind tunnel. The working section is long enough for the flow to have become very nearly invariant with streamwise distance. In order to be systematic, the flow profile generators of Irwin-type spires and surface roughness were the same for both neutral and stable conditions. Achieving the required profiles by adjusting the flow generators, even for neutral flow, is a highly iterative art, and the present results indicate that it will be no less iterative for a stable flow (as well as there being more conditions to meet), so this was not attempted in the present investigation. The stable-case flow conformed in most respects to Monin–Obukhov similarity in the surface layer. A linear temperature profile was applied at the working section inlet, resulting in a near-linear profile in the developed flow above the boundary layer and ‘strong’ imposed stability, while the condition at the surface was ‘weak’. Aerodynamic roughness length (mean velocity) was not affected by stability even though the roughness Reynolds number ${<}1$ , while the thermal roughness length was much smaller, as is to be expected. The neutral case was Reynolds-number independent, and by inference, the stable case was also Reynolds-number independent. 相似文献
9.
While the importance of baroclinicity in determining the structure of the planetary boundary layer (PBL) is well recognized, the actual effect of baroclinicity on the structure is not well understood. Results based on simulations obtained using the turbulent kinetic energy-dissipation rate of turbulent kinetic energy closure model of the turbulent flow in a neutral baroclinic PBL provide additional insight into the role of baroclinicity. The baroclinic PBL is characterized by significant shear production of turbulent kinetic energy throughout the complete boundary-layer depth. The turbulent mixing length is bounded by the presence of a stable temperature inversion layer indicating that the depth of the baroclinic PBL is determined by the inversion height. Significant turbulent shear stresses exist throughout the baroclinic PBL and the air is relatively well-mixed except in the surface layer. 相似文献
10.
Zbigniew Sorbjan 《Boundary-Layer Meteorology》2012,142(1):21-31
Empirical similarity functions of the Richardson number, obtained from bin-averaged data in the lower part of the stable boundary
layer, show an undesired dependence on height at which the observations are collected. A correction of this flaw is proposed
and tested by employing the neutral mixing length l
o
as a similarity scale for height. The function of height describing l
o
is assumed to be linear in the surface layer, and approaching a specified value with increasing height. The modification
does not alter the dependence of similarity functions on the Richardson number, and is shown to be supported by the Cooperative
Atmospheric-Surface Exchange Study-1999 (CASES-99) data. 相似文献
11.
John J. Carroll 《Boundary-Layer Meteorology》1993,65(1-2):137-158
A simple time-dependent one-dimensional model of the planetary boundary layer (PBL) is described and used to examine the degree to which model design decisions affect model output variables. The model's sensitivity to changes in the environmental conditions is also explored. Averages of the surface fluxes, near-ground wind speeds and other PBL properties from 48 h simulations are compared to control runs. The model-calculated surface fluxes are most sensitive, in decreasing order of importance, to the vertical grid spacing, the form of closure between the surface temperature and the atmosphere, the use of vertical diffusivity smoothing, the choice of maximum time step and choice of turbulence closure scheme. These fluxes are relatively insensitive to mixing-length scaling or choice of implicit time step weighting factor. Sensitivity to changes in soil type exceeds any of the design criteria tested. The modeled fluxes are moderately sensitive to small variations in the horizontal pressure gradient, to unsteadiness in the geostrophic wind and to variations in surface roughness. They are relatively insensitive to uncertainties in local vertical velocities and small (25%) variations applied separately to soil thermal diffusivity or heat capacity. The sensitivity of the average PBL depth (Z
i
) to model and environmental changes are similar to those of surface fluxes except thatZ
i
is more sensitive to changes in mixing length, albedo and imposed vertical velocity then are the surface fluxes. 相似文献
12.
Osamu Chiba 《Boundary-Layer Meteorology》1984,29(4):313-319
Several experimental results indicate that S
w (the skewness of the vertical turbulent velocity) increases with height, and K
w (the kurtosis) decreases with height in the neutral surface layer. The measured behavior of S
w and K
w with height under neutral conditions is shown to be consistent with available models for the gradient-diffusion and the pressure-velocity correlation. In addition, an estimate of the mode of the probability density distribution turns out to be helpful in interpreting the height dependence of K
w. 相似文献
13.
Daewon W. Byun 《Boundary-Layer Meteorology》1991,57(1-2):17-48
Functional forms of the universal similarity functions A, B (for wind components parallel and normal to the surface stress), and C (for potential temperature difference) are determined based on the generalized theory of the resistance laws for the Planetary Boundary Layer (PBL). The similarity-profile functions for the surface layer are matched with the velocity and temperature-defect profiles that are assumed to have shapes modified by certain powers of nondimensional height z/h, where h is the PBL height. The powers of the outer-layer profile functions are determined, so that the functions become negligible in the surface layer. To close the temperature defect law, an assumption that the temperature gradient across the top of the PBL is continuous with the stratification of the overlying atmosphere is used. The result of this assumption is that nondimensional momentum and temperature profiles in the PBL can be described in terms of four basic ratios: (1) roughness ratio = /h (2) scale-height ratio =|f|h/u*, (3) ambient stratification parameter =h/*, and (4) stability parameter =h/L, where L is the Monin-Obukhov length, z0 is the surface roughness, is the upper-air stratification, u
* is the friction velocity, and
* is the temperature scale at the surface. For stable conditions, the scale-height ratio can be related to the atmospheric stability and the upperair stratification, and the generalized similarity and Rossby number similarity theories become identical. Under appropriate boundary conditions, function A is explicitly dependent on the stability parameter , while B is a function of scale-height ratio , which in turn depends on the stability. Function C is shown to be dependent on the stability and the upper-air stratification, due to the closure assumption used for the temperature profile.The suggested functional forms are compared with other empirical approximations by several authors. The general framework used to determine the functional forms needs to be tested against good boundary-layer measurements. 相似文献
14.
An acoustic Doppler sounder has been used to document the behaviour of the stable atmospheric boundary layer during the “Coast” experiment, in April-May, 1983, on a homogeneous terrain near the Dutch coast. It has been shown that kaimal's model of the spectrum of velocity in the stable surface layer can be applied and that surface-layer parameterization can be used in the whole stable surface layer. Velocity spectra have been computed between .0005 c.p.s. and .1 c.p.s. and for the stability range for z/L between 0 and 10. It is to be noted that the information has been obtained using only sodar data. 相似文献
15.
The dependence on atmospheric stability of flow characteristics adjacent to a very rough surface was investigated in a larch
forest in Japan. Micrometeorological measurements of three-dimensional wind velocity and air temperature were taken at two
heights above the forest, namely 1.7 and 1.2 times the mean canopy height h. Under near-neutral and stable conditions, the observed turbulence statistics suggest that the flow was likely to be that
of the atmospheric surface layer (ASL) at 1.7h, and of the roughness sublayer (RSL) at 1.2h. However, in turbulence spectra, canopy-induced large coherent motions appeared clearly at both heights. Even under strongly
stable conditions, the large-scale motions were retained at 1.2h, whereas they were overwhelmed by small-scale motions at 1.7h. This phenomenon was probably due to the enhanced contribution of the ASL turbulence associated with nocturnal decay of the
RSL depth, because the small-scale motions appeared at frequencies close to the peak frequencies of well-known ASL spectra.
This result supports the relatively recent concept that canopy flow is a superimposition of coherent motions and the ASL turbulence.
The large-scale motions were retained in temperature spectra over a wider region of stability compared to streamwise wind
spectra, suggesting that a canopy effect extended higher up for temperature than wind. The streamwise spacing of dominant
eddies according to the plane mixing-layer analogy was only valid in a narrow range at near neutral, and it was stabilised
at nearly half its value under stable conditions. 相似文献
16.
Kapil Chauhan Nicholas Hutchins Jason Monty Ivan Marusic 《Boundary-Layer Meteorology》2013,147(1):41-50
Two-point correlations of the fluctuating streamwise velocity are examined in the atmospheric surface layer over the salt flats of Utah’s western desert, and corresponding structure inclination angles are obtained for neutral, stable and unstable conditions. The neutral surface-layer results supplement evidence for the invariance of the inclination angle given in Marusic and Heuer (Phys Rev Lett 99:114504, 2007). In an extension of those results it is found that the inclination angle changes drastically under different stability conditions in the surface layer, varying systematically with the Monin–Obukhov stability parameter in the unstable regime. The variation is parametrized and subsequently can be used to improve existing near-wall models in the large-eddy simulation of the atmospheric surface layer. 相似文献
17.
We investigate the effect of the assimilation of surface and boundary-layer mass-field observations on the planetary boundary
layer (PBL) within a one-dimensional (1D) version of the non-hydrostatic Fifth-Generation Pennsylvania State University/National
Center for Atmospheric Research Mesoscale Model (MM5). We focus on the vertical extent and effects of mass-field nudging within
the PBL based on surface observations, and the added value of assimilating column mass observations within the PBL. Model
experiments for dynamic initialization and dynamic analysis are conducted and composited for 29 May, 6 June, and 7 June 2002
during the International H2O Project (IHOP) over the Southern Great Plains, U.S.A. Advantages are found when the data assimilation uses the innovation
(the difference between the modelled value and the observed value) calculated by comparing the surface mass-field observation
to the model value at the 2-m observation height rather than at the lowest model level. It is shown that this innovation can
be applied throughout the model-diagnosed PBL via nudging during free-convective conditions because of the well-mixed nature
of the PBL. However, in stable conditions, due to decreased vertical mixing the surface innovation may be best applied only
in a shallow layer adjacent to the surface. Surface air-temperature innovations were also applied to the top soil-layer temperature
to minimize disruption to the surface energy balance. In combination with the surface observations, the use of within-PBL
mass-field data assimilation improves the simulated PBL structure. 相似文献
18.
An important parameterization in large-eddy simulations (LESs) of high- Reynolds-number boundary layers, such as the atmospheric
boundary layer, is the specification of the surface boundary condition. Typical boundary conditions compute the fluctuating
surface shear stress as a function of the resolved (filtered) velocity at the lowest grid points based on similarity theory.
However, these approaches are questionable because they use instantaneous (filtered) variables, while similarity theory is
only valid for mean quantities. Three of these formulations are implemented in simulations of a neutral atmospheric boundary
layer with different aerodynamic surface roughness. Our results show unrealistic influence of surface roughness on the mean
profile, variance and spectra of the resolved velocity near the ground, in contradiction of similarity theory. In addition
to similarity-based surface boundary conditions, a recent model developed from an a priori experimental study is tested and it is shown to yield more realistic independence of the results to changes in surface roughness.
The optimum value of the model parameter found in our simulations matches well the value reported in the a priori wind-tunnel study. 相似文献
19.
The results from a one-dimensional photochemical model of the troposphere representative of summertime conditions at Northern Hemisphere mid-latitudes are presented. A parameterization of mixing processes within the planetary boundary layer (PBL) has been incorporated into the model for both the daytime convective PBL and the formation of the nocturnal PBL. One result of the parameterized PBL is that the concentrations of some trace species in the free troposphere are 20–30% higher than when mixing processes are described by a vertical eddy diffusion coefficient which is held constant with respect to height and time.The calculations indicate that the lifetime of the oxides of nitrogen (NO
x
=NO+NO2) against photochemical conversion to nitric acid (HNO3) during summertime conditions is on the order of 6 h. This lifetime is short enough to deplete most of the NO
x
in the PBL, resulting in the finding that other reactive nitrogen species (HNO3 and peroxyacetyl nitrate) are more abundant than NO
x
throughout the free troposphere, even though NO
x
is the most abundant reactive nitrogen species at the surface. The effects of the inclusion of anthropogenic nonmethane hydrocarbon (NMHC) chemistry are also discussed. The inclusion of NMHC chemistry has a pronounced effect on the photochemistry of tropospheric oxone and increases thein situ column production by more than 30%. 相似文献
20.
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