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1.
Timothy Delsole 《Surveys in Geophysics》2004,25(2):107-149
Atmospheric and oceanic eddies are believed to be manifestations of quasigeostrophic turbulence — turbulence that occurs in
rapidly rotating, vertically stratified fluid systems. The heat, momentum, and water transport by these eddies constitute
a significant component of the climate balance, without which climate change cannot be understood. A major, unsolved problem
is whether the turbulent eddy fluxes can be parameterized in terms of the large-scale, background flow. In the past, stochastic
models have been used quite extensively to investigate quasigeostrophic turbulence in the case in which the eddy statistics
are isotropic and homogeneous. Unfortunately, these models ignore the background shear which is absolutely essential to maintaining
the eddies in the presence of dissipation. Recent attempts to extend stochastic models to shear flows have shown significant
skill in predicting the structure of the eddy fluxes in arbitrary, three-dimensionally varying flows. This paper provides
an accessible introduction to these models. The topics reviewed include quasigeostrophic turbulence and two-dimensional turbulence,
non-modal andoptimal perturbations, mathematical theory of stochastic models, stochastic model simulations with realistic
background states, and recent closure theories. A list of unsolved problems concludes this review. 相似文献
2.
Proper Orthogonal Decomposition （POD） provides a powerful modal transformation tool for stochastic dynamics. In this paper, coherency matrix-based proper orthogonal decomposition （CPOD） is presented as an innovative form of the POD based on cross power spectral density matrices. By introducing a discretizing scheme, the CPOD-based spectral representation method is obtained for use in stochastic simulation. Moreover, some criteria are proposed that allow the truncation order of CPOD to be conveniently determined. A numerical example to illustrate the application of the proposed method for the simulation of a wind velocity field is provided. 相似文献
3.
Nonlinear singular vectors and nonlinear singular values 总被引：2，自引：0，他引：2
MU Mu 《中国科学D辑(英文版)》2000,43(4):375-385
A novel concept of nonlinear singular vector and nonlinear singular value is introduced, which is a natural generalization of the classical linear singular vector and linear singular value to the nonlinear category. The optimization problem related to the determination of nonlinear singular vectors and singular values is formulated. The general idea of this approach is demonstrated by a simple two-dimensional quasigeostrophic model in the atmospheric and oceanic sciences. The advantage and its applications of the new method to the predictability, ensemble forecast and finite-time nonlinear instability are discussed. This paper makes a necessary preparation for further theoretical and numerical investigations. 相似文献
4.
The oceanic mixed layer (OML) response to an idealized hurricane with different propagation speeds is investigated using a
two-layer reduced gravity ocean model. First, the model performances are examined with respect to available observations relative
to Hurricane Frances (2004). Then, 11 idealized simulations are performed with a Holland (Mon Weather Rev 108(8):1212–1218,
1980) symmetric wind profile as surface forcing with storm propagation speeds ranging from 2 to 12 m s−1. By varying this parameter, the phasing between atmospheric and oceanic scales is modified. Consequently, it leads to different
momentum exchanges between the hurricane and the OML and to various oceanic responses. The present study determines how OML
momentum and heat budgets depend on this parameter. The kinetic energy flux due to surface wind stress is found to strongly
depend on the propagation speed and on the cross-track distance from the hurricane center. A resonant regime between surface
winds and near-inertial currents is clearly identified. This regime maximizes locally the energy flux into the OML. For fast-moving
hurricanes (>6 m s−1), the ratio of kinetic energy converted into turbulence depends only on the wind stress energy input. For slow-moving hurricanes
(<6 m s−1), the upwelling induced by current divergence enhances this conversion by shallowing the OML depth. Regarding the thermodynamic
response, two regimes are identified with respect to the propagation speed. For slow-moving hurricanes, the upwelling combined
with a sharp temperature gradient at the OML base formed in the leading part of the storm maximizes the oceanic heat loss.
For fast propagation speeds, the resonance mechanism sets up the cold wake on the right side of the hurricane track. These
results suggest that the propagation speed is a parameter as important as the surface wind speed to accurately describe the
oceanic response to a moving hurricane. 相似文献
5.
In this study,the characteristics of turbulence transport and intermittency and the evolutionary mechanisms were studied in different pollution stages of heavy haze weather from December 2016 to January 2017 in the Beijing area using the method developed by Ren et al.(2019) as the automatic identification of atmospheric spectral gaps and the reconstruction of atmospheric turbulence sequences.The results reveal that turbulence intermittency is the strongest in the cumulative stage(CS)of heavy haze weather,followed by in the transport stage(TS),and it is the weakest in the dissipation stage(DS).During the development and accumulation of haze pollution,buoyancy contributes negatively to turbulent kinetic energy(TKE),and horizontal wind speed is low.The classical turbulent motion is often affected by submesoscale motion.As a result,the calculation results of turbulence parameters are affected by submesoscale motion,which causes intensified turbulence intermittency.During the dissipation of pollution,the downward momentum transfer induced by low-level jets provides kinetic energy for turbulent motion in the near surface layer.The turbulent mixing effect is enhanced,and intermittency is weakened.Due to the intermittency of atmospheric turbulence,turbulence parameters calculated from the original fluctuation of meteorological elements may be overestimated.The overestimation of turbulence parameters in the CS is the strongest,followed by the TS,and the DS is the weakest.The overestimation of turbulent fluxes results in an overestimation of atmospheric dissipation capability that may cause an underestimation of pollutant concentrations in the numerical simulations of air quality. 相似文献
6.
Abstract Severe unidirectional Fourier truncation of the equations for 2-D incompressible flow leads to a system of three coupled PDEs in one space dimension with the same quadratic invariants as the original set (i.e. energy and enstrophy). Numerically generated equilibria for inviscid, truncated versions of the reduced system are well approximated by Kraichnan's energy-enstrophy equipartition spectra. Viscous calculations for decaying turbulence at moderate resolution (1024 degrees of freedom) also appear to be consistent with a direct, k ?3, enstrophy cascading inertial range when the dissipation is small. Dissipation range intermittency in the form of spatially intermittent enstrophy dissipation with occasional strong bursts producing linear phase locking is also observed. In contrast to full 2-D simulations, no tendency towards the emergence of isolated, coherent vorticity structures is observed. The model consequently mimics some, but not all, of the properties of the full 2-D set. 相似文献
7.
Vortex merger is a phenomenon characterizing the whole class of geophysical vortices, from atmospheric storms and large oceanic eddies up to small scale turbulence. Here we focus on the merger of subsurface oceanic anticyclones in an idealized primitive equations model. This study has been motivated by past and recent observations of colliding lens-like anticyclones off of Gibraltar Strait. The critical conditions for merger (critical merger distance and time needed for merger) are determined. We will show that the predictions of classical two-dimensional merger are not verified for subsurface isolated vortices. For instance, critical merger distances will be reduced because of the vortex potential vorticity (PV) structure. The post-merger characteristics of the vortex (radius, extension and PV), are also determined. Merger-related effects, like production of peripheral filaments and small-scale eddies are also investigated and suggest the contribution of merger in both direct and inverse energy cascades. 相似文献
8.
用1985～1995年期间海洋角动量变化序列和大气角动量变化序列,分析它们对Chandler摆动的激发能量以及它们与天文观测激发的相干性. 结果表明，在Chandler摆动频带内，海洋角动量变化提供的激发能量大约占观测激发的64髎，其中洋底压力变化起主导作用；NCEP/NCAR(美国国家环境预测中心/国家大气研究中心)和JMA(日本气象厅)大气角动量变化提供的激发能量分别为观测激发的23髎和214髎. 海洋激发与观测激发的相干系数约为0.52，接近99髎置信度下限(0.54)，海洋激发的相位滞后观测激发约19°；NCEP/NCAR和JMA的大气激发与观测激发的相干系数分别为0.32和0.37，大气激发的相位超前观测激发分别约47°和19°. 用更短期间(9年、6年)的海洋和大气角动量序列与更长期间(16、39年)的大气角动量序列作分析表明，在Chandler摆动频带内，无论是它们的激发能量，还是它们与观测激发之间的相干系数都呈现很大的变化，而且这些变化具有某种程度的随机性. 相似文献
9.
The radiative energy budget of the middle atmosphere and its parameterization in general circulation models 总被引：1，自引：0，他引：1
The thermal regime of the middle atmosphere is determined to a great extent by the balance between the incoming solar and outgoing infrared radiation. To account for these processes in numerical models of the middle atmosphere, parameterizations that are capable of quickly and accurately calculating infrared cooling and solar heating rates are required. These parameterizations should include the breakdown of local thermodynamic equilibrium (LTE) conditions and allow for feedbacks by ensuring that dependencies on all input parameters are accounted for. This paper discusses the major mechanisms responsible for maintaining the radiative energy budget of the middle atmosphere and presents a brief review of approaches and numerical schemes currently available for use in general circulation models. The main focus of the paper is on the approaches and schemes designed for non-LTE treatment. 相似文献
10.
Mostafa Bakhoday Paskyabi 《Ocean Dynamics》2016,66(11):1429-1448
The dispersion and transport of single inertial particles through an oscillatory turbulent aquatic environment are examined numerically by a Lagrangian particle tracking model using a series of idealised test cases. The turbulent mixing is incorporated into the Lagrangian model by the means of a stochastic scheme in which the inhomogeneous turbulent quantities are governed by a one-dimensional k- ε turbulence closure scheme. This vertical mixing model is further modified to include the effects of surface gravity waves including Coriolis-Stokes forcing, wave breaking, and Langmuir circulations. To simplify the complex interactions between the deterministic and the stochastic phases of flow, we assume a time-invariant turbulent flow field and exclude the hydrodynamic biases due to the effects of ambient mean current. The numerical results show that the inertial particles acquire perturbed oscillations traced out as time-varying sinking/rising orbits in the vicinity of the sea surface under linear and cnoidal waves and acquire a non-looping single arc superimposed with the high-frequency fluctuations beneath the nonlinear solitary waves. Furthermore, we briefly summarise some recipes through the course of this paper on the implementation of the stochastic particle tracking models to realistically describe the drift and suspension of inertial particles throughout the water column. 相似文献
11.
12.
AbstractRiver basins are by definition temporally-varying systems: changes are apparent at every temporal scale, in terms of changing meteorological inputs and catchment characteristics due to inherently uncertain natural processes and anthropogenic interventions. In an operational context, the ultimate goal of hydrological modelling is predicting responses of the basin under conditions that are similar or different to those observed in the past. Since water management studies require that anthropogenic effects are considered known and a long hypothetical period is simulated, the combined use of stochastic models, for generating the inputs, and deterministic models that also represent the human interventions in modified basins, is found to be a powerful approach for providing realistic and statistically consistent simulations (in terms of product moments and correlations, at multiple time scales, and long-term persistence). The proposed framework is investigated on the Ferson Creek basin (USA) that exhibits significantly growing urbanization during the last 30 years. Alternative deterministic modelling options include a lumped water balance model with one time-varying parameter and a semi-distributed scheme based on the concept of hydrological response units. Model inputs and errors are respectively represented through linear and nonlinear stochastic models. The resulting nonlinear stochastic framework maximizes the exploitation of the existing information by taking advantage of the calibration protocol used in this issue. 相似文献
13.
《中国科学:地球科学(英文版)》2015,(11)
In situ observations and numerical simulations of turbulence are essential to understanding vertical mixing processes and their dynamical controls on both physical and biogeochemical processes in coastal embayments. Using in situ data collected by bottom-mounted acoustic Doppler current profilers(ADCPs) and a free-falling microstructure profiler, as well as numerical simulations with a second-moment turbulence closure model, we studied turbulence and mixing in the Xiamen Bay, a freshwater-influenced tidal bay located at the west coast of the Taiwan Strait. Dynamically, the bay is driven predominantly by the M2 tide, and it is under a significant influence of the freshwater discharged from the Jiulong River. It is found that turbulence quantities such as the production and dissipation rates of the turbulent kinetic energy(TKE) were all subject to significant tidal variations, with a pronounced ebb-flood asymmetry. Turbulence was stronger during flood than ebb. During the flooding period, the whole water column was nearly well mixed with the depth-averaged TKE production rate and vertical eddy viscosity being up to 5?10?6 W kg?1 and 2?10?2 m2 s?1, respectively. In contrast, during the ebb strong turbulence was confined only to a 5?8 m thick bottom boundary layer, where turbulence intensity generally decreases with distance from the seafloor. Diagnosis of the potential energy anomaly showed that the ebb-flood asymmetry in turbulent dissipation and mixing was due mainly to tidal straining process as a result of the interaction between vertically shared tidal currents and horizontal density gradients. The role of vertical mixing in generating the asymmetry was secondary. A direct comparison of the modeled and observed turbulence quantities confirmed the applicability of the second-moment turbulence closure scheme in modeling turbulent processes in this weakly stratified tidally energetic environment, but also pointed out the necessity of further refinements of the model. 相似文献
14.
A. M. Treguier 《地球物理与天体物理流体动力学》2013,107(1-4):43-68
Abstract Steady currents develop in oceanic turbulence above topography even in the absence of steady forcing. Mesoscale steady currents are correlated with mesoscale topography with anticyclonic eddies above topographic bumps, and large scale westward flows develop when β is non-zero. The relationship between those two kinds of steady currents, as well as their dependence on various parameters, is studied using a barotropic quasi-geostrophic channel model. The percentage of steady energy is found to depend on the forcing, friction and topography in a non-monotonic fashion. For example, the percentage of steady currents grows with the energy level in the linear regime (low energies) and decreases when the energy level increases in the nonlinear regime (high energies). Mesoscale steady currents are the energy source for the steady westward flow U, and therefore U is the maximum when large scale and mesoscale currents are of the same order of magnitude. This happens when the ratio S of the large scale slope βH/f 0 and the mesoscale rms topographic slope α is of order one. U decreases for both small and large values of S. 相似文献
15.
LIU ShaoLin LI XiaoFan WANG WenShuai LIU YouShan ZHANG MeiGen & ZHANG Huan 《中国科学:地球科学(英文版)》2014,57(4):751-758
Here we introduce generalized momentum and coordinate to transform seismic wave displacement equations into Hamiltonian system. We define the Lie operators associated with kinetic and potential energy, and construct a new kind of second order symplectic scheme, which is extremely suitable for high efficient and long-term seismic wave simulations. Three sets of optimal coefficients are obtained based on the principle of minimum truncation error. We investigate the stability conditions for elastic wave simulation in homogeneous media. These newly developed symplectic schemes are compared with common symplectic schemes to verify the high precision and efficiency in theory and numerical experiments. One of the schemes presented here is compared with the classical Newmark algorithm and third order symplectic scheme to test the long-term computational ability. The scheme gets the same synthetic surface seismic records and single channel record as third order symplectic scheme in the seismic modeling in the heterogeneous model. 相似文献
16.
A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations
Nash'at Ahmad Zafer Boybeyi Rainald Löhner Ananthakrishna Sarma 《Pure and Applied Geophysics》2007,164(1):217-244
In recent years there has been a growing interest in using Godunov-type methods for atmospheric flow problems. Godunov's unique
approach to numerical modeling of fluid flow is characterized by introducing physical reasoning in the development of the
numerical scheme (van Leer, 1999). The construction of the scheme itself is based upon the physical phenomenon described by the equation sets. These
finite volume discretizations are conservative and have the ability to resolve regions of steep gradients accurately, thus
avoiding dispersion errors in the solution. Positivity of scalars (an important factor when considering the transport of microphysical
quantities) is also guaranteed by applying the total variation diminishing condition appropriately. This paper describes the implementation of a Godunov-type finite volume scheme based on unstructured
adaptive grids for simulating flows on the meso-, micro- and urban-scales. The Harten-Lax-van Leer-Contact (HLLC) approximate
Riemann solver used to calculate the Godunov fluxes is described in detail. The higher-order spatial accuracy is achieved
via gradient reconstruction techniques after van Leer and the total variation diminishing condition is enforced with the aid of slope-limiters. A multi-stage explicit Runge-Kutta time marching scheme is used for
maintaining higher-order accuracy in time. The scheme is conservative and exhibits minimal numerical dispersion and diffusion.
The subgrid scale diffusion in the model is parameterized via the Smagorinsky-Lilly turbulence closure. The scheme uses a non-staggered mesh arrangement of variables (all quantities are
cell-centered) and requires no explicit filtering for stability. A comparison with exact solutions shows that the scheme can
resolve the different types of wave structures admitted by the atmospheric flow equation set. A qualitative evaluation for
an idealized test case of convection in a neutral atmosphere is also presented. The scheme was able to simulate the onset
of Kelvin-Helmholtz type instability and shows promise in simulating atmospheric flows characterized by sharp gradients without
using explicit filtering for numerical stability. 相似文献
17.
We derive conservative time-dependent structured discretizations and two-way embedded (nested) schemes for multiscale ocean dynamics governed by primitive equations (PEs) with a nonlinear free surface. Our multiscale goal is to resolve tidal-to-mesoscale processes and interactions over large multiresolution telescoping domains with complex geometries including shallow seas with strong tides, steep shelfbreaks, and deep ocean interactions. We first provide an implicit time-stepping algorithm for the nonlinear free-surface PEs and then derive a consistent time-dependent spatial discretization with a generalized vertical grid. This leads to a novel time-dependent finite volume formulation for structured grids on spherical or Cartesian coordinates, second order in time and space, which preserves mass and tracers in the presence of a time-varying free surface. We then introduce the concept of two-way nesting, implicit in space and time, which exchanges all of the updated fields values across grids, as soon as they become available. A class of such powerful nesting schemes applicable to telescoping grids of PE models with a nonlinear free surface is derived. The schemes mainly differ in the fine-to-coarse scale transfers and in the interpolations and numerical filtering, specifically for the barotropic velocity and surface pressure components of the two-way exchanges. Our scheme comparisons show that for nesting with free surfaces, the most accurate scheme has the strongest implicit couplings among grids. We complete a theoretical truncation error analysis to confirm and mathematically explain findings. Results of our discretizations and two-way nesting are presented in realistic multiscale simulations with data assimilation for the middle Atlantic Bight shelfbreak region off the east coast of the USA, the Philippine archipelago, and the Taiwan–Kuroshio region. Multiscale modeling with two-way nesting enables an easy use of different sub-gridscale parameterizations in each nested domain. The new developments drastically enhance the predictive capability and robustness of our predictions, both qualitatively and quantitatively. Without them, our multiscale multiprocess simulations either were not possible or did not match ocean data. 相似文献
18.
Geostrophic turbulence is a key paradigm in the current understanding of the large-scale planetary circulations. It implies
that a flow is turbulent, rotating, stably stratified, and in near-geostrophic balance. When a small-scale forcing is present,
geostrophic turbulence features an inverse energy cascade. When the meridional variation of the Coriolis parameter (or a β-effect) is included, the horizontal flow symmetry breaks down giving rise to the emergence of jet flows. The presence of
a large-scale drag ensures that the flow attains a steady state. Dependent on the governing parameters, four steady-state
flow regimes are possible, two of which are considered in this study. In one of these regimes, a flow is dominated by the
drag while in the other one, the recently discovered regime of zonostrophic turbulence, a flow becomes strongly anisotropic
and features slowly evolving systems of alternating zonal jets. Zonostrophic turbulence is distinguished by anisotropic inverse
energy cascade and emergence of a new class of nonlinear waves known as zonons. In addition, meridional scalar diffusion is
strongly modified in this regime. This paper provides an overview of various regimes of turbulence with a β-effect, elaborates main characteristics of friction-dominated and zonostrophic turbulence, elucidates the physical nature
of the zonons, discusses the meridional diffusion processes in different regimes, and relates these results to oceanic observations. 相似文献
19.
Nonlinearity and complexity in gravel bed dynamics 总被引：1，自引：1，他引：0
Arvind Singh Stefano Lanzoni Efi Foufoula-Georgiou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(7):967-975
The dynamics of river bed evolution are known to be notoriously complex affected by near-bed turbulence, the collective motion
of clusters of particles of different sizes, and the formation of bedforms and other large-scale features. In this paper,
we present the results of a study aiming to quantify the inherent nonlinearity and complexity in gravel bed dynamics. The
data analyzed are bed elevation fluctuations collected via submersible sonar transducers at 0.1 Hz frequency in two different
settings of low and high discharge in a controlled laboratory experiment. We employed surrogate series analysis and the transportation
distance metric in the phase-space to test for nonlinearity and the finite size Lyapunov exponent (FSLE) methodology to test
for complexity. Our analysis documents linearity and underlying dynamics similar to that of deterministic diffusion for bed
elevations at low discharge conditions. These dynamics transit to a pronounced nonlinearity and more complexity for high discharge,
akin to that of a multiplicative cascading process used to characterize fully developed turbulence. Knowing the degree of
nonlinearity and complexity in the temporal dynamics of bed elevation fluctuations can provide insight into model formulation
and also into the feedbacks between near-bed turbulence, sediment transport and bedform development. 相似文献
20.
Igor Esau 《Ocean Dynamics》2014,64(5):689-705
A turbulence-resolving parallelized atmospheric large-eddy simulation model (PALM) has been applied to study turbulent interactions between the humid atmospheric boundary layer (ABL) and the salt water oceanic mixed layer (OML). The most energetic three-dimensional turbulent eddies in the ABL–OML system (convective cells) were explicitly resolved in these simulations. This study considers a case of shear-free convection in the coupled ABL–OML system. The ABL–OML coupling scheme used the turbulent fluxes at the bottom of the ABL as upper boundary conditions for the OML and the sea surface temperature at the top of the OML as lower boundary conditions for the ABL. The analysis of the numerical experiment confirms that the ABL–OML interactions involve both the traditional direct coupling mechanism and much less studied indirect coupling mechanism (Garrett Dyn Atmos Ocean 23:19–34, 1996). The direct coupling refers to a common flux-gradient representation of the air–sea exchange, which is controlled by the temperature difference across the air–water interface. The indirect coupling refers to thermal instability of the Rayleigh–Benard convection, which is controlled by the temperature difference across the entire mixed layer through formation of the large convective eddies or cells. The indirect coupling mechanism in these simulations explained up to 45 % of the ABL–OML co-variability on the turbulent scales. Despite relatively small amplitude of the sea surface temperature fluctuations, persistence of the OML cells organizes the ABL convective cells. Water downdrafts in the OML cells tend to be collocated with air updrafts in the ABL cells. The study concludes that the convective structures in the ABL and the OML are co-organized. The OML convection controls the air–sea turbulent exchange in the quasi-equilibrium convective ABL–OML system. 相似文献