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1.
Daniel Reinert Volkmar Wirth Joachim Eichhorn Walter-Georg Panhans 《Boundary-Layer Meteorology》2007,125(1):109-132
This paper presents the dry version of a new large-eddy simulation (LES) model, which is designed to simulate air flow and
clouds above highly complex terrain. The model is three-dimensional and nonhydrostatic, and the governing equations are sound
filtered by use of the anelastic approximation. A fractional step method is applied to solve the equations on a staggered
Cartesian grid. Arbitrarily steep and complex orography can be accounted for through the method of viscous topography. The
dynamical model core is validated by comparing the results for a spreading density current against a benchmark solution. The
model accuracy is further assessed through the simulation of turbulent flow across a quasi two-dimensional ridge. The results
are compared with wind-tunnel data. The method of viscous topography is not restricted to moderately sloped terrain. Compared
to models using curvilinear grids, it allows this model to be applied to a much wider range of flows. This is illustrated
through the simulation of an atmospheric boundary-layer flow over a surface mounted cube. The results show that the dry model
version is able to accurately represent the complex flow in the vicinity of three-dimensional obstacles. It is concluded that
the method of viscous topography was successfully implemented into a micrometeorological LES model. As will be shown in Part
II, this allows the detailed study of clouds in highly complex terrain. 相似文献
2.
Xiaohua Yang 《Boundary-Layer Meteorology》1991,54(1-2):183-208
Nonhydrostatic effects in two-dimensional mesoscale sea breeze systems are investigated by numerical simulations. It is shown that nonhydrostatic effects are directly contributed by the vertical gradients of the vertical velocity variance as well as by the vertical accelerations. It is also shown that a K-type turbulence closure is not suitable in a nonhydrostatic primitive equation model, and a higher-order closure scheme should therefore be used. Results from hydrostatic and fully-nonhydrostatic models are compared for various surface and atmospheric background conditions, such as scale and strength of surface heating, geostrophic wind, stability, surface roughness contrast, Coriolis effect, etc. It is found that for strongly developed sea breeze cases, vertical gradients of vertical velocity variance contribute most to nonhydrostatic forcing in the lower layers, and that the resultant nonhydrostatic pressure gradient acts against the hydrostatic pressure gradient, so that nonhydrostatic simulations produce weaker systems than hydrostatic ones. For weak sea breeze systems, the difference between the two models tends to be small. 相似文献
3.
Hann-Ming H. Juang 《Meteorology and Atmospheric Physics》1992,50(1-3):75-88
Summary The set of fully compressible nonhydrostatic equations governing a broad spectrum of atmospheric motion was transformed fromz coordinates to sigma coordinates under a hydrostatic base state. The hydrostatic base state may be either time-independent, such as a hydrostatic balance with-out motion or with motion such as a thermal wind balance, or time-dependent such as might be obtained from the result of integrating a hydrostatic model. The transformed set of equations can be used to predict and study all scales of at mospheric phenomena.The set of perturbation equations was also derived under the same condition. The computational sensitivity in computation of pressure gradient force in sigma coordinate can be improved by computing the pressure gradient interms of perturbations under a certain hydrostatic state.The hydrostatic regional spectral model developed by Juang and Kanamitsu (1991) was modified to be a nonhydrostatic spectral model based on the nonhydrostatic equations in sigma coordinates with time-dependent hydrostatic base states. A semi-implicit time integration scheme was used. Two experiments were performed to test this nonhydrostatic spectral model with acceptable results.With 7 Figures 相似文献
4.
给出了在旋转坐标系中考虑重力加速度g的空间变化的大气控制方程组,并证明了大气总质量和总能量的守恒性,以及和取常值g时得到的结果相一致的动、位能和动、内能之间的转换关系.还讨论了在球坐标系中应用方程组时可能出现的困难,给出了在高度近似下在该系中考虑g的空间变化的方案,它可以用来建立完全弹性的非静力模式. 相似文献
5.
With the development of numerical weather prediction technology,the traditional global hydrostatic models used in many countries of the world for operational weather forecasting and numerical simulations of general circulation have become more and more unfit for high-impact weather prediction.To address this,it is important to invest in the development of global nonhydrostatic models.Few existing nonhydrostatic global models use consistently the grid finite difference scheme for the primitive equations of dynamical cores,which can subsequently degrade the accuracy of the calculations.A new nonhydrostatic global spectral model,which utilizes the Eulerian spectral method,is developed here from NCAR Community Atmosphere Model 3.0(CAM3.0).Using Janjic's hydrostatic/nonhydrostatic method,a global nonhydrostatic spectral method for the primitive equations has been formulated and developed.In order to retain the integrity of the nonhydrostatic equations,the atmospheric curvature correction and eccentricity correction are considered. In this paper,the Held-Suarez idealized test and an idealized baroclinic wave test are first carried out,which shows that the nonhydrostatic global spectral model has similar climate states to the results of many other global models for long-term idealized integration,as well as better simulation ability for short-term idealized integration.Then,a real case experiment is conducted using the new dynamical core with the full physical parameterizations of subgrid-scale physical processes.The 10-day numerical integration indicates a decrease in systematic error and a better simulation of zonal wind,temperature,and 500-hPa height. 相似文献
6.
Recently, new hyperbolic systems of equations that can be used to describe smooth flows accurately in both the atmosphere and oceans have been developed. These ‘approximate systems’ are derived by slowing down the speed of the fast waves instead of increasing their speed to infinity as in the primitive equations. The approximate systems have a number of theoretical advantages over the traditional systems. The practical implications of some of these advantages have already been demonstrated for the oceanic case. There is another advantage of the new systems that has not been discussed extensively. A model based on either of the new systems can be used to describe different scales of motion, e.g. the large, medium, or small scale. In addition, a mechanism is provided for a smooth transition between these scales. The incorporation of topography into the approximate systems has also not been discussed. To demonstrate the multiscale nature of the transformed systems in the presence of topography, numerical results from a model based on the approximate system for meteorology are compared with analytic solutions for three topographic scales. Removing the horizontal means of the density and pressure, which was necessary to obtain the proper scaling of the equations in the original papers, reduces the truncation error associated with a transformed system near steep mountains. For example, in the atmospheric case a second-order method requires only approximately 10 points across the base of the mountain to achieve a 1% relative error for any of the three topographic solutions during the relevant time scale of the associated motion. 相似文献
7.
Summary Atmospheric flows exhibit long-range spatiotemporal correlations manifested as the fractal geometry to the global cloud cover pattern concomitant with inverse power law form for power spectra of temporal fluctuations on all space-tie scales ranging from turbulence (centimetersseconds) to climate (kilometers-years). Long-range spatiotemporal correlations are ubiquitous to dynamical systems in nature and are identified as signatures ofself-organized criticality. Standard models in meteorological theory cannot explain satisfactorily the observed self-organized criticality in atmospheric flows. Mathematical models for simulation and prediction of atmospheric flows are nonlinear and do not possess analytical solutions. Finite precision computer realizations of nonlinear models give unrealistic solutions because ofdeterministic chaos, a direct consequence of round-off error growth in iterative numerical computations. Recent studies show that roundoff error doubles on an average for each iteration of iterative computations. Round-off error propagates to the main stream computation and gives unrealistic solutions in numerical weather prediction (NWP) and climate models which incorporate thousands of iterative computations in long-term numerical integration schemes. An alternative non-deterministic cell dynamical system model for atmospheric flows described in this paper predicts the observed self-organized criticality as intrinsic to quantumlike mechanics governing flow dynamics. The model provides universal quantification for self-organized criticality in terms of the statistical normal distribution. Model predictions are in agreement with a majority of observed spectra of time series of several standard climatological data sets representative of disparate climatic regimes. Universal spectrum for natural climate variability rules out linear trends. Man-made greenhouse gas related atmospheric warming will result in intensification of natural climate variability, seen immediately in high frequency fluctuations such as QBO and ENSO and even shorter timescales. Model concepts and results of analyses are discussed with reference to possible prediction of climate change.With 11 Figures 相似文献
8.
Effects of terrain-following vertical coordinates on high-resolution NWP simulations 总被引：5，自引：3，他引：2 
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下载免费PDF全文 With increasing resolution in numerical weather prediction(NWP)models,the model topography can be described with finer resolution and includes steeper slopes.Consequently,negative effects of the traditional terrain-following vertical coordinate on high-resolution numerical simulations become more distinct due to larger errors in the pressure gradient force(PGF)calculation and associated distortions of the gravity wave along the coordinate surface.A series of numerical experiments have been conducted in this study,including idealized test cases of gravity wave simulation over a complex mountain,error analysis of the PGP estimation over a real topography,and a suite of real-data test cases.The GRAPES-Meso model is utilized with four different coordinates,i.e.,the traditional terrain-following vertical coordinate proposed by Gal-Chen and Somerville(hereinafter referred to as the Gal.C.S coordinate),the one-scale smoothed level(SLEVE1),the two-scale smoothed level(SLEVE2),and the COSINE(COS)coordinates.The results of the gravity wave simulation indicate that the GRAPES-Meso model generally can reproduce the mountain-induced gravity waves,which are consistent with the analytic solution.However,the shapes,vertical structures,and intensities of the waves are better simulated with the SLEVE2 coordinate than with the other three coordinates.The model with the COS coordinate also performs well,except at lower levels where it is not as effective as the SLEVE2 coordinate in suppressing the PGF errors.In contrast,the gravity waves simulated in both the Gal.C.S and SLEVE1 coordinates are relatively distorted.The estimated PGF errors in a rest atmosphere over the real complex topography are much smaller(even disappear at the middle and upper levels)in the GRAPES-Meso model using the SLEVE2 and COS coordinates than those using the Gal.C.S and SLEVE1 coordinates.The results of the real-data test cases conducted over a one-month period suggest that the three modified vertical coordinates(SLEVE1,SLEVE2,and COS coordinates)give better results than the traditional Gal.C.S coordinate in terms of forecasting bias and root mean square error,and forecasting anomaly correlation coefficients.In conclusion,the SLEVE2 coordinate is proved to be the best option for the GRAPES-Meso model. 相似文献
9.
An ensemble of random-phase internal gravity waves is considered in the dynamical framework of the Euler–Boussinesq equations. For flows with zero mean potential vorticity, a kinetic equation for the mean spectral energy density of the waves is obtained under hypothesis of Gaussian statistics with zero correlation length. Stationary scaling solutions of this equation are found for almost vertically propagating waves. The resulting spectra are anisotropic in vertical and horizontal wave numbers. For flows with small but non-zero mean potential vorticity, under the same statistical hypothesis applied to the wave part of the flow, it is shown that the vortex part and the wave part decouple. The vortex part obeys a limiting slow dynamics equation exhibiting vertical collapse and layering which may contaminate the wave-part spectra. Relation of these results to the in situ atmospheric measurements and previous work on oceanic gravity waves is discussed. 相似文献
10.
Tilt corrections over complex terrain and their implication for CO<Subscript>2</Subscript> transport
Jielun Sun 《Boundary-Layer Meteorology》2007,124(2):143-159
Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called
tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow
objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics
of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations.
We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the
canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the
diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest
canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have
a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate
system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate
system and its implication in investigation of CO2 transport are discussed.
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
A parameterization of the nonhydrostatic pressure was modified and adapted to a nonlinear numerical model of the neutral atmospheric boundary layer. A hydrostatic model and the quasinonhydrostatic version were used to simulate neutral flow over a symmetrical hill of uniform roughness. Mean-flow quantities and some turbulence characteristics of the flow from both models are presented. These results were compared with observations, analytic theory, and other numerical models.The quasi-nonhydrostatic method produced qualitative features commonly observed in such flows that the hydrostatic model could not simulate. For instance, the observed velocity reduction at the hill base and the speedup at the summit both were simulated by the quasi-nonhydrostatic model. However, computation of vertical velocities from the incompressible continuity equation is inadequate above regions of recirculation and presents a limitation to the method.Journal Paper No. J-12741 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2779. 相似文献
12.
Flow over Hills: A Large-Eddy Simulation of the Bolund Case 总被引：6，自引：6，他引：0
Marc Diebold Chad Higgins Jiannong Fang Andreas Bechmann Marc B. Parlange 《Boundary-Layer Meteorology》2013,148(1):177-194
Simulation of local atmospheric flows around complex topography is important for several applications in wind energy (short-term wind forecasting and turbine siting and control), local weather prediction in mountainous regions and avalanche risk assessment. However, atmospheric simulation around steep mountain topography remains challenging, and a number of different approaches are used to represent such topography in numerical models. The immersed boundary method (IBM) is particularly well-suited for efficient and numerically stable simulation of flow around steep terrain. It uses a homogenous grid and permits a fast meshing of the topography. Here, we use the IBM in conjunction with a large-eddy simulation (LES) and test it against two unique datasets. In the first comparison, the LES is used to reproduce experimental results from a wind-tunnel study of a smooth three-dimensional hill. In the second comparison, we simulate the wind field around the Bolund Hill, Denmark, and make direct comparisons with field measurements. Both cases show good agreement between the simulation results and the experimental data, with the largest disagreement observed near the surface. The source of error is investigated by performing additional simulations with a variety of spatial resolutions and surface roughness properties. 相似文献
13.
14.
一个包含土壤和植被的区域气候模式及其性能检验 总被引：4，自引：0，他引：4
本文研制了一个三维地气耦合的区域气候模式，该模式由大气、土壤和植被三个子模式组成，各子模式间通过动量、能量和水份交换过程进行相互作用。在大气子模式中提出用z-z*混合坐标系处理地形的新方法，并把诊断分析中的散度修订方案引入数值模式，使其在物理依据上更加合理。此外，模式中较为详细地考虑了影响区域气候形成和变化的物理过程。简单的数值试验表明，区域气候模式比较真实地模拟了土壤和植被冠层的温度日变化，对区域气候平均态也有一定的模拟能力，可较好地处理大地形，具有良好的稳定性能，并对下垫面热力非均匀性的响应也是敏感的。 相似文献
15.
Xiaohua Yang 《Boundary-Layer Meteorology》1993,65(4):401-424
This paper describes a nonhydrostatic and incompressible mesoscale model formulation using a terrain-following coordinate system. A tensor transformation procedure is used to derive a diagnostic equation for the nonhydrostatic pressure field. The model features a simplified second-order turbulence closure scheme. The two-dimensional version of the nonhydrostatic model, as well as the corresponding hydrostatic model, are applied to simulate stably stratified airflow over mesoscale bell-shaped mountain ridges. The results show that the nonhydrostatic model is capable of simulating nonhydrostatic dynamics of mesoscale lee wave systems such as the trapped wave phenomenon. 相似文献
16.
Glacier valleys across the Transantarctic Mountains are not properly taken into account in climate models, because of their coarse resolution. Nonetheless, glacier valleys control katabatic winds in this region, and the latter are thought to affect the climate of the Ross Sea sector, frsater formation to snow mass balance. The purpose of this paper is to investigate the role of the production of turbulent kinetic energy by the subgrid-scale orography in the Transantarctic Mountains using a 20-km atmospheric regional model. A classical orographic roughness length parametrization is modified to produce either smooth or rough valleys. A one-year simulation shows that katabatic winds in the Transantarctic Mountains are strongly improved using smooth valleys rather than rough valleys. Pressure and temperature fields are affected by the representation of the orographic roughness, specifically in the Transantarctic Mountains and over the Ross Ice Shelf. A smooth representation of escarpment regions shows better agreement with automatic weather station observations than a rough representation. This work stresses the need to improve the representation of subgrid-scale orography to simulate realistic katabatic flows. This paper also provides a way of improving surface winds in an atmospheric model without increasing its resolution. 相似文献
17.
A nonhydrostatic model based on a new approach 总被引：4，自引：0，他引：4
Z. I. Janjic 《Meteorology and Atmospheric Physics》2003,82(1-4):271-285
Summary ?The nonhydrostatic Meso model developed at NCEP (Janjic et al, 2001) is based on a new approach. Namely, a hydrostatic NWP
model using mass based vertical coordinate has been extended to include the nonhydrostatic motions. In this way favorable
features of the hydrostatic formulation have been preserved. This procedure did not require any linearization or approximation.
The nonhydrostatic dynamics has been introduced through an add-on module. The nonhydrostatic module can be turned on and off,
so that easy comparison can be made of hydrostatic and nonhydrostatic solutions.
Here, the basic philosophy behind the discretization methods applied in the model, and not covered by Janjic et al (2001),
is discussed, and the latest developments are reviewed. The forecast examples shown indicate that significant differences
between hydrostatic and nonhydrostatic forecasts may develop even at relatively coarse resolution of 8 km. Possible future
developments are considered.
Received May 7, 2001; revised October 15, 2001 相似文献
18.
Summary A completely new nonhydrostatic model system known as the Advanced Regional Prediction System (ARPS) has been developed in
recent years at the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma. The ARPS is designed
from the beginning to serve as an effective tool for basic and applied research and as a system suitable for explicit prediction
of convective storms as well as weather systems at other scales. The ARPS includes its own data ingest, quality control and
objective analysis packages, a data assimilation system which includes single-Doppler velocity and thermodynamic retrieval
algorithms, the forward prediction component, and a self-contained post-processing, diagnostic and verification package.
The forward prediction component of the ARPS is a three-dimensional, nonhydrostatic compressible model formulated in generalized
terrain-following coordinates. Minimum approximations are made to the original governing equations. The split-explicit scheme
is used to integrate the sound-wave containing equations, which allows the horizontal domain-decomposition strategy to be
efficiently implemented for distributed-memory massively parallel computers. The model performs equally well on conventional
shared-memory scalar and vector processors. The model employs advanced numerical techniques, including monotonic advection
schemes for scalar transport and variance-conserving fourth-order advection for other variables. The model also includes state-of-the-art
physics parameterization schemes that are important for explicit prediction of convective storms as well as the prediction
of flows at larger scales.
Unique to this system are the consistent code styling maintained for the entire model system and thorough internal documentation.
Modern software engineering practices are employed to ensure that the system is modular, extensible and easy to use.
The system has been undergoing real-time prediction tests at the synoptic through storm scales in the past several years over
the continental United States as well as in part of Asia, some of which included retrieved Doppler radar data and hydrometeor
types in the initial condition.
As the first of a two-part paper series, we describe herein the dynamic and numerical framework of the model, together with
the subgrid-scale turbulence and the PBL parameterization. The model dynamic and numerical framework is then verified using
idealized and realistic mountain flow cases and an idealized density current. Other physics parameterization schemes will
be described in Part II, which is followed by verification against observational data of the coupled soil-vegetation model,
surface layer fluxes and the PBL parameterization. Applications of the model to the simulation of an observed supercell storm
and to the prediction of a real case are also found in Part II. In the latter case, a long-lasting squall line developed and
propagated across the eastern part of the United States following a historical number of tornado outbreak in the state of
Arkansas.
Received April 14, 2000 Revised July 17, 2000 相似文献
19.
Based on previous research results on river re-distribution models, a modification on the effects of topographic slopes for a runoff parameterization was proposed and implemented to the NCAR＇s land sur face model (LSM). This modification has two aspects: firstly, the topographic slopes cause outflows from higher topography and inflows into the lower topography points; secondly, topographic slopes also cause decrease of infiltration at higher topography and increases of infiltration at lower topography. Then changes in infiltration result in changes in soil moisture, surface fluxes and then in surface temperature, and eventual ly in the upper atmosphere and the climate. This mechanism is very clearly demonstrated in the point bud gets analysis at the Andes Mountains vicinities. Analysis from a regional scale perspective in the Mackenzie GEWEX Study (MAGS) area, the focus of the ongoing Canadian GEWEX program, shows that the modi fied runoff parameterization does bring significant changes in the regional surface climate. More important ly, detailed analysis from a global perspective shows many encouraging improvements introduced by the modified LSM over the original model in simulating basic atmospheric climate properties such as thermodynamic features (temperature and humidity). All of these improvements in the atmospheric climate simulation illustrate that the inclusion of topographic effects in the LSM can force the AGCM to produce a more realistic model climate. 相似文献
20.
Modeling nonhydrostatic atmospheric flow requires the solution of the vertical equation of motion and a prognostic or diagnostic equation for pressure. If the nonhydrostatic components of the flow are relatively small, they can be approximated and incorporated into a purely hydrostatic model, which usually is conceptually simpler and computationally more efficient. A method to do this for a linear model of local thermally-induced circulations is further developed and adapted to a non-linear numerical model of the neutral atmospheric boundary layer. A hydrostatic model and the quasi-nonhydrostatic version were used to simulate neutral flow over simple terrain features. One set of observations taken over a simple change in roughness and another set taken over a change in both roughness and terrain were simulated by both models to assess the capabilities of the quasi-nonhydrostatic technique.It is found that (as expected) the pressure deviation from the hydrostatic state is negligible for the roughness change, but it is an important aspect of neutral flow over terrain. Thus, for flow encountering a simple roughness change, the hydrostatic approximation is good, even for small horizontal scales. However, the quasi-nonhydrostatic model qualitatively produces the features in the observations for flow over a terrain change that the hydrostatic model cannot produce.Journal Paper No. J-12737 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2779. 相似文献