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1.
Toward very high horizontal resolution NWP over the alps: Influence of increasing model resolution on the flow pattern 总被引：1，自引：0，他引：1
Michał Z. Ziemiański Marcin J. Kurowski Zbigniew P. Piotrowski Bogdan Rosa Oliver Fuhrer 《Acta Geophysica》2011,59(6):1205-1235
The increasing resolution of contemporary regional numerical weather prediction (NWP) models, reaching horizontal grid sizes
of O(1 km), requires robust and reliable dynamical cores, working well beyond the approximation of quasi-horizontal flows. That
stimulates an interest in an application for NWP purposes of dynamical cores based on the anelastic, or — more generally —
sound-proof flow equations, and characterized by appropriate robustness and reliability. The paper presents results from testing
the dynamical core of EULAG, the anelastic research model for multi-scale flows, as a prospective NWP dynamical core. The
model simulates the semi-realistic frictionless and adiabatic flow over realistic steep Alpine topographies, employing horizontal
grid sizes of 2.2, 1.1, and 0.55 km. The paper demonstrates not only the numerical robustness of EULAG, but also studies the
influence of the varying horizontal resolution on the simulated flow. Results show that the increased horizontal resolution
increases orographic drag on the flow. While the general flow pattern remains the same, increased resolution influences the
flow on scales from hundreds of kilometers to meso-gamma scales. The differences are especially apparent in the near-surface
layer of 1.5 to 3 km deep, and in the distribution and amplitudes of the orographically-induced gravity waves. 相似文献
2.
The anelastic nonhydrostatic model EULAG is a candidate for the future dynamical core of a numerical weather prediction model.
Achieving such an objective requires a number of experiments focused on testing correctness of the solutions and robustness
of the solver. In the spirit of this idea, a set of tests related to standard atmospheric problems was performed, of which
the two regarding development and evolution of a supercell were employed as benchmarks of moist dynamics of the model. Their
results are discussed in this paper. Development and evolution of a stormsystem with a set of characteristic features such
as stormsplitting along with the generation of horizontal vorticity and cold pool formation is investigated. In addition,
the influence of domain geometry, boundary conditions and subgrid-scale mixing is examined. 相似文献
3.
为了研究大气静力平衡适应过程的本质,利用波动理论和能量转换角度,分别对完全可压缩的等温大气模型、滞弹近似下的等温大气模型和层结中性大气模型进行研究比较.结果表明：大气静力平衡适应过程的本质是声波和混合声重力波对扰动能量的频散过程,滞弹近似模型和层结中性模型均不能完全描述此适应过程;在波动假设下,此三类大气模型中扰动物理量之间的偏振关系同波动的性质有关,气团的运动方程均为椭圆方程,声波和混合声重力波对气团运动的作用差异较显著.
大气静力平衡适应过程中扰动能量以有效势能、有效弹性势能、动能或波动能量的形式存在并相互转换;扰动有效势能与其他形式能量之间的转换与混合声重力波或者重力内波有关,扰动有效弹性势能与其他形式能量之间的转换与声波有关.在完全可压缩的等温大气模型中,扰动有效势能增加1个单位,其中69.9%来自扰动垂直动能,其余30.1%来自扰动有效弹性势能. 相似文献
大气静力平衡适应过程中扰动能量以有效势能、有效弹性势能、动能或波动能量的形式存在并相互转换;扰动有效势能与其他形式能量之间的转换与混合声重力波或者重力内波有关,扰动有效弹性势能与其他形式能量之间的转换与声波有关.在完全可压缩的等温大气模型中,扰动有效势能增加1个单位,其中69.9%来自扰动垂直动能,其余30.1%来自扰动有效弹性势能. 相似文献
4.
5.
A semi-implicit edge-based unstructured-mesh model is developed that integrates nonhydrostatic soundproof equations, inclusive of anelastic and pseudo-incompressible systems of partial differential equations. The model builds on nonoscillatory forward-in-time MPDATA approach using finite-volume discretization and unstructured meshes with arbitrarily shaped cells. Implicit treatment of gravity waves benefits both accuracy and stability of the model. The unstructured-mesh solutions are compared to equivalent structured-grid results for intricate, multiscale internal-wave phenomenon of a non-Boussinesq amplification and breaking of deep stratospheric gravity waves. The departures of the anelastic and pseudoincompressible results are quantified in reference to a recent asymptotic theory [Achatz et al. 2010, J. Fluid Mech., 663, 120–147)]. 相似文献
6.
EULAG is a computational model for simulating flows across a wide range of scales and physical scenarios. A standard option
employs an anelastic approximation to capture nonhydrostatic effects and simultaneously filter sound waves from the solution.
In this study, we examine a localized gravity wave packet generated by instabilities in Held-Suarez climates. Although still
simplified versus the Earth’s atmosphere, a rich set of planetary wave instabilities and ensuing radiated gravity waves can arise. Wave packets
are observed that have lifetimes ≤ 2 days, are negligibly impacted by Coriolis force, and do not show the rotational effects
of differential jet advection typical of inertia-gravity waves. Linear modal analysis shows that wavelength, period, and phase
speed fit the dispersion equation to within a mean difference of ∼ 4%, suggesting an excellent fit. However, the group velocities
match poorly even though a propagation of uncertainty analysis indicates that they should be predicted as well as the phase
velocities. Theoretical arguments suggest the discrepancy is due to nonlinearity — a strong southerly flow leads to a critical
surface forming to the southwest of the wave packet that prevents the expected propagation. 相似文献
7.
Nedjeljka ?agar 《Pure and Applied Geophysics》2012,169(3):367-379
This paper reports recent advances in understanding of dynamical aspects of the tropical data assimilation. In contrast with
the mid-latitudes, there is no a well-defined approach for the tropical data assimilation in numerical weather prediction
(NWP) community which has traditionally been concentrated on the mid-latitude analysis problem. In particular, the impact
of the equatorial Rossby, inertio-gravity, and mixed Rossby-gravity waves on the tropical forecast-error covariances is difficult
to quantify. Various tropical waves are characterized by different couplings between the mass field and the wind field. The
average mixture of these waves, built into the background-error covariance matrix for data assimilation provides analysis
increments which appear nearly univariate even though they result from the advanced multivariate assimilation methodology.
This applies to both dry and moist idealized tropical systems as well as to a 4D-Var NWP assimilation system. 相似文献
8.
The validity of the anelastic approximation has recently been questioned in the regime of rapidly-rotating compressible convection in low Prandtl number fluids (Calkins, Julien and Marti, Proc. R. Soc. A, 2015, vol. 471, 20140689). Given the broad usage and the high computational efficiency of sound-proof approaches in this astrophysically relevant regime, this paper clarifies the conditions for a safe application. The potential of the alternative pseudo-incompressible approximation is investigated, which in contrast to the anelastic approximation is shown to never break down for predicting the point of marginal stability. Its accuracy, however, decreases close to the parameters corresponding to the failure of the anelastic approach, which is shown to occur when the sound-crossing time of the domain exceeds a rotation time scale, i.e. for rotational Mach numbers greater than one. Concerning the supercritical case, which is naturally characterised by smaller rotational Mach numbers, we find that the anelastic approximation does not show unphysical behaviour. Growth rates computed with the linearised anelastic equations converge toward the corresponding fully compressible values as the Rayleigh number increases. Likewise, our fully nonlinear turbulent simulations, produced with our fully compressible and anelastic models and carried out in a highly supercritical, rotating, compressible, low Prandtl number regime show good agreement. However, this nonlinear test example is for only a moderately low convective Rossby number of 0.14. 相似文献
9.
Abstract A two-dimensional, nonlinear, time-dependent, non-hydrostatic, anelastic, numerical model is used to assess the effect of condensation on the evolution and structure of gravity waves generated by the passage of a stable, moist stream over topography. Precipation is ignored but water phase changes are taken into account explicitly. The main effect of condensation is to damp the wave intensity and to reduce the wave drag, which can be diminished by as much as 50% compared to its value in dry simulations. This result agrees with some earlier analytical models and some more recent fully compressible numerical models. This model also confirms that the presence of condensation delays the overturning of isentropes, and the formation of the critical layer that accompanies wave-breaking. 相似文献
10.
Zbigniew P. Piotrowski Andrzej A. Wyszogrodzki Piotr K. Smolarkiewicz 《Acta Geophysica》2011,59(6):1294-1311
This paper highlights progress with the development of a petascale implementation of general-purpose high-resolution (nonoscillatory)
hydrodynamical simulation code EULAG [Prusa et al. 2008, Comput. Fluids
37, 1193]. The applications addressed are anelastic atmospheric flows in the range of scales from micro to planetary. The new
modeldomain decomposition into a three dimensional processor array has been implemented to increase model performance and
scalability. The performance of the new code is demonstrated on the IBM BlueGene/L and Cray XT4/XT5 supercomputers. The results
show significant improvement of the model efficacy compared to the original decomposition into a two-dimensional processor
array in the horizontal — a standard in meteorological models. 相似文献
11.
Numerical modelling ofSH wave seismograms in media whose material properties are prescribed by a random distribution of many perfectly elastic cavities and by intrinsic absorption of seismic energy (anelasticity) demonstrates that the main characteristics of the coda waves, namely amplitude decay and duration, are well described by singly scattered waves in anelastic media rather than by multiply scattered waves in either elastic or anelastic media. We use the Boundary Integral scheme developed byBenites
et al. (1992) to compute the complete wave field and measure the values of the direct waveQ and coda wavesQ in a wide range of frequencies, determining the spatial decay of the direct wave log-amplitude relation and the temporal decay of the coda envelope, respectively. The effects of both intrinsic absorption and pure scattering on the overall attenuation can be quantified separately by computing theQ values for corresponding models with (anelastic) and without (elastic) absorption. For the models considered in this study, the values of codaQ
–1 in anelastic media are in good agreement with the sum of the corresponding scatteringQ
–1 and intrinsicQ
–1 values, as established by the single-scattering model ofAki andChouet (1975). Also, for the same random model with intrinsic absorption it appears that the singly scattered waves propagate without significant loss of energy as compared with the multiply scattered waves, which are strongly affected by absorption, suggesting its dominant role in the attenuation of coda waves. 相似文献
12.
This paper describes implementation of the warm-rain bin microphysics in a LES model based on the EULAG fluid flow solver.
The binmicrophysics EULAG is applied to the case of shallow nonprecipitating tropical convection to investigate the impact
of the secondary activation of cloud droplets above the cloud base. In a previous study applying the EULAG model with the
double-moment bulk warm-rain microphysics scheme, the in-cloud activation was shown to have significant implications for the
mean microphysical and optical characteristics of the cloud field. By contrasting the simulations with and without in-cloud
activation as in the previous study, we show that the in-cloud activation has qualitatively similar but quantitatively smaller
effect. In particular, the concentration of cloud droplets in the bin simulation without in-cloud activation decreases with
height not as strongly as in corresponding simulations applying the double-moment bulk scheme. 相似文献
13.
Josef Brechler 《Studia Geophysica et Geodaetica》1990,34(1):65-77
Summary This article deals with some problems connected with the formulation of a non-hydrostatic mesoscale model of airflow in the atmosphere. Due to an irregular surface a terrain-following coordinate system is used and the equations of the model are transformed into this system. Sound waves are eliminated by the use of the anelastic approximation. The influence of boundaries is minimized by the use of open boundary conditions at the lateral boundaries of the computational domain and of the absorbing layer beneath the upper boundary. 相似文献
14.
Convection in the Earth’s core is usually studied in the Boussinesq approximation in which the compressibility of the liquid is ignored. The density of the Earth’s core varies from ICB to CMB by approximately 20%. The question of whether we need to take this variation into account in core convection and dynamo models is examined. We show that it is in the thermodynamic equations that differences between compressible and Boussinesq models become most apparent. The heat flux conducted down the adiabat is much smaller near the inner core boundary than it is near the core-mantle boundary. In consequence, the heat flux carried by convection is much larger nearer the inner core boundary than it is near the core-mantle boundary. This effect will have an important influence on dynamo models. Boussinesq models also assume implicitly that the rate of working of the gravitational and buoyancy forces, as well as the Ohmic and viscous dissipation, are small compared to the heat flux through the core. These terms are not negligible in the Earth’s core heat budget, and neglecting them makes it difficult to get a thermodynamically consistent picture of core convection. We show that the usual anelastic equations simplify considerably if the anelastic liquid approximation, valid if αT?1, where α is the coefficient of expansion and T a typical core temperature, is used. The resulting set of equations are not significantly more difficult to solve numerically than the usual Boussinesq equations. The relationship of our anelastic liquid equations to the Boussinesq equations is also examined. 相似文献
15.
In this study an incompressible smoothed particle hydrodynamics (ISPH) approach coupled with the sediment erosion model is developed to investigate the sediment bed scour and grain movement under the dam break flows. Two-phase formulations are used in the ISPH numerical algorithms to examine the free surface and bed evolution profiles, in which the entrained sediments are treated as a different fluid component as compared with the water. The sediment bed erosion model is based on the concept of pick-up flow velocity and the sediment is initiated when the local flow velocity exceeds a critical value. The proposed model is used to reproduce the sediment erosion and follow-on entrainment process under an instantaneous dam break flow and the results are compared with those from the weakly compressible moving particle semi-implicit (WCMPS) method as well as the experimental data. It has been demonstrated that the two-phase ISPH model performed well with the experimental data. The study shows that the ISPH modelling approach can accurately predict the dynamic sediment scouring process without the need to use empirical sediment transport formulas. 相似文献
16.
V. P. Trubitsyn 《Izvestiya Physics of the Solid Earth》2008,44(12):1018-1026
A system of equations for the calculation of thermal convection in a compressible mantle with variable parameters and phase transitions is derived from the general laws of mass, momentum, and energy conservation and thermodynamic relations. Mantle convection is successively calculated in the anelastic liquid, truncated anelastic liquid, mean density, expanded Boussinesq, and Boussinesq approximations. Phase transitions are automatically taken into account with the help of effective thermodynamic parameters determined from general thermodynamic relations. 相似文献
17.
Abstract We study the nonlinear stability of MHD waves propagating in a two-dimensional, compressible, highly magnetized, viscous plasma. These waves are driven by a weak, shear body force which could be imposed by large scale internal fluctuations present in the solar atmosphere. The effects of anisotropic viscosity (leading to a cubic damping) and of the nonlinear coupling of the Alfven and the magnetoacoustic waves are analysed using Galerkin and multiple-scale analysis: the MHD equations are reduced to a set of nonlinear ordinary differential equations which is then suitably truncated to give a model dynamical system, representing the interaction of two complex Galerkin modes. For propagation oblique to the background magnetic field, analytical integration shows that the low-wavenumber mode is physically unstable. For propagation parallel to the background magnetic field the high-wavenumber wave can undergo saddlenode bifurcations, in way that is similar to the van der Pol oscillator; these bifurcations lead to the appearance of a hysteresis cycle. A numerical integration of the dynamical system shows that a sequence of Hopf bifurcations takes place as the Reynolds number is increased, up to the onset of nonperiodic behaviour. It also shows that energy can be transferred from the low- wavenumber to the high-wavenumber mode. 相似文献
18.
Estimation of Elastic Moduli in a Compressible Gibson Half-space by Inverting Rayleigh-wave Phase Velocity 总被引：3，自引：1，他引：3
A Gibson half-space model (a non-layered Earth model) has the shear modulus varying linearly with depth in an inhomogeneous
elastic half-space. In a half-space of sedimentary granular soil under a geostatic state of initial stress, the density and
the Poisson’s ratio do not vary considerably with depth. In such an Earth body, the dynamic shear modulus is the parameter
that mainly affects the dispersion of propagating waves. We have estimated shear-wave velocities in the compressible Gibson
half-space by inverting Rayleigh-wave phase velocities. An analytical dispersion law of Rayleigh-type waves in a compressible
Gibson half-space is given in an algebraic form, which makes our inversion process extremely simple and fast. The convergence
of the weighted damping solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method.
Calculation efficiency is achieved by reconstructing a weighted damping solution using singular value decomposition techniques.
The main advantage of this algorithm is that only three parameters define the compressible Gibson half-space model. Theoretically,
to determine the model by the inversion, only three Rayleigh-wave phase velocities at different frequencies are required.
This is useful in practice where Rayleigh-wave energy is only developed in a limited frequency range or at certain frequencies
as data acquired at manmade structures such as dams and levees. Two real examples are presented and verified by borehole S-wave
velocity measurements. The results of these real examples are also compared with the results of the layered-Earth model. 相似文献
19.
Babatunde J. Abiodun William J. Gutowski Abayomi A. Abatan Joseph M. Prusa 《Acta Geophysica》2011,59(6):1158-1167
This study evaluates the capability of a non-hydrostatic global climate model with grid stretching (CEU) that uses NCAR Community
Atmospheric Model (CAM) physics and EULAG dynamics. We compare CEU rainfall with that produced by CAM using finite volume
dynamics (CFV). Both models simulated climate from 1996 to 2000, using the same parameterization schemes. 相似文献
20.
A low-order model of the unforced, inviscid barotropic model is examined as a dynamical system. Analytic solutions, consisting of linear and nonlinear oscillations (Rossby waves), are obtained in appropriate limiting initial conditions. These solutions are periodic. With less restrictive initial conditions the system shows quasi-periodic behaviour at low energies and chaotic behviour at high energies. This transition is accompanied by frequency-locking and period-doubling. Quasi-periodic and chaotic behaviour may coëxist in phase space for the same values of the model invariants. The results are interpreted in terms of perturbed integrable Hamiltonian systems. Considerations of the low-frequency variability of the atmosphere are also made. 相似文献