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A Numerical Study of geostrophic adjustment and Frontogenesis

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Advances in Atmospheric Sciences 1998年第2期15卷 46-59页

作者：伍荣生 Department of Atmospheric Sciences Nanjing University Nanjing

Using the PSU/NCAR Mesoscale Model version four(MM4), the frontogenesis and geostrophic adjustment problem in atmosphere with imbalance initial ideal data and conditions are studied. Based on results of experiments, it is found that the objective analysis and initialization procedure of the Model are not sensitive to the initial conditions used in this study. The final state of atmosphere, through process of adjustment, depends on the temperature gradient intensity of initial imbalance conditions. The front can be formed with appropriate condition. The processes of the frontogenesis are studied. It is also found that the response of the model to the ideal initial data used in this investigation is sensitive to the selected lateral boundary condition. The time-dependent inflow/outflow lateral boundary condition is the best implemented option for this numerical study. Energetic study of the experiments shows that the front is formed after the initial transient stage when there is no exchange of energy between the kinetic and potential energy. The time needed for the formation of the front is longer than that predicted theoretically. The ratio of kinetic energy to the released potential energy is considered. This ratio varies with the temperature gradient intensity and the type of used wind for computing kinetic energy (geostrophic or geostrophic plus ageostrophic wind). The larger temperature gradient, the larger magnitude of this ratio. A maximum value of energy in either type of computed kinetic energies (geostrophic wind kinetic energy and actual wind kinetic energy) for cases that the fronts are observed whereby, and its magnitude and occurrence time depend on initial data distribution. The variation of the computed kinetic energies with time, after transition time, is reasonable and no significant conversion of the energy between kinetic and potential energy goes on, however, stability within variables is not achieved.

关键词： Frontogenesis geostrophic adjustment Energetics of geostrophic adjustment

Topographic Effect on the Energetics of geostrophic adjustment

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Acta meteorologica Sinica 2005年第1期19卷 19-30页

作者：方娟伍荣生易爱民 The Key Laboratory of Mesoscale Severe Weather Nanjing University Nanjing 210093 Guangzhou Central Meteorological Observatory Guangzhou 510080

In this work, the impact of topography on the geostrophic adjustment processis discussed with a simple two-layer shallow water model, in which the lower-layer fluid isinitially stationary while the upper-layer is perturbed by the impulsive injection of *** the geostrophic adjustment process of this ideal model, the initial kinetic energy isreleased and a fraction of it is converted into potential energy of the final geostrophicallyadjusted state. Thus, after the geostrophic adjustment, the kinetic energy of the system is reducedwhile the potential energy is enhanced. As the topographic effect is considered, it is found thatthe decrease of the kinetic energy (ΔKE) and the increase of the potential energy (ΔPE) of thesystem are weakened as compared to the case that the lower boundary is flat. Furthermore, thetopographic effect on APE is less pronounced than that on ΔKE, which implicates that the topographytends to inhibit the energy dispersion of the inertio-gravity wave. The numerical simulation of thegeostrophic adjustment process shows that, due to the impact of topography, the convergence anddivergence in the low layer are reduced and the undulation of the interface between the lower-layerand upper-layer is weakened. This means that the amplitude of the inertio-gravity wave is decreased,and thus, the energy radiated by the inertio-gravity wave is lessened.

关键词： geostrophic adjustment topography kinetic energy potential energy energydispersion energy conversion ratio transfer

THE INFLUENCE OF STRATIFICATION ON FRONTOGENESIS CAUSED BY geostrophic adjustment

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Acta meteorologica Sinica 1998年第3期12卷 376-381页

作者：王云峰伍荣生 Laboratory of Mesoscale Severe Weather and Department of Atmospheric Sciences Nanjing University Nanjing 210093

A uniform,inviscid,incompressible fluid in a two-dimensional plane(x,z)is considered. Three principles:conservation of potential vorticity,conservation of absolute momentum,and conservation of mass are used for this *** the initial mass field and the initial wind field do not satisfy geostrophic balance,then through geostrophic adjustment under suitable conditions, the frontogenesis will finally *** work points out that the initial density distribution greatly influences the frontal *** the stratification in cold air is the same as that in warm air,two frontogeneses will occur at top and bottom boundaries *** the stratification in cold air is larger than that in warm air,the frontogenesis at the bottom boundary still exists,but the other at the top boundary *** result makes us further understand the mechanism of the frontogenesis in the real atmosphere.

关键词： mesoscale weather geostrophic adjustment frontogenesis

INVESTIGATION ON geostrophic adjustment,FRONTOGENESIS AND OSCILLATIONS

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Acta meteorologica Sinica 2001年第3期15卷 346-355页

作者： PAN Yinong(潘益农) WU Rongsheng(伍荣生) The Key Laboratory of Mesosacle Severe Weather Department of Atmospheric SciencesNanjing University Nanjing 210093 The Key Laboratory of Mesosacle Severe Weather Department of Atmospheric SciencesNanjing University Nanjing 210093

geostrophic adjustment and frontogenesis are examined by means of the 2-D ARPS model. The simulation shows *** the large-scale forcing,both the frontogenesis and frontolysis are observed during the geostrophic adjustment process and the intensity of the front oscillates in the case of no *** convergence (divergence) induced by the secondary circulation is the most important factor for frontogenesis (frontolysis) at the top and bottom *** amplitude and period of oscillation are dependent on the initial atmospheric stratification and the Coriolis frequency,and they are related to the inertio-gravity wave.

关键词： geostrophic adjustment frontogenesis and frontolysis inertio-gravity oscillation

Meridional deflection of global eddy propagation derived from tandem altimetry: Mechanism and implication

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Science China Earth Sciences 2024年第3期67卷 811-825页

作者： Ge CHEN Xiaoyan CHEN Frontiers Science Center for Deep Ocean Multispheres and Earth System School of Marine TechnologyOcean University of ChinaQindao 266100China Laboratory for Regional Oceanography and Numerical Modeling Laoshan LaboratoryQindao 266237China

A common view on meridional deflection of eddy propagation is poleward for cyclones and equatorward for anticyclones. This widely accepted polarity-sensitive pattern has been increasingly undermined given that it is systematically violated on both zonal and regional scales as recently reported. Here, we approach the problem by exploring these violations in terms of eddy effects of spatiotemporal geostrophy, thermal fading, and flow dragging, yielding the following main conclusions.(1) The polarity-dependent deflection discrepancy is a pseudo feature resulting from a biased fit to the normalized eddy tracks which are spatially asymmetric(though azimuthally symmetric) between the two signs;Instead, the primary pattern of eddy deflection appears to be geographically correlated and polarity independent.(2) geostrophic adjustment plays a critical role in defining the meridional movement of an eddy. Specifically, a consistent poleward(equatorward) trajectory bending of spatially(temporally) ageostrophic eddies is observed irrespective of their polarity.(3) The mechanism of eddy deflection is also determined by its zonal propagation direction. Westward propagating eddies are substantially affected by thermal fading, while opposite ones by flow dragging. A realistic and comprehensive understanding of eddy deflection mechanisms serves as a significant contribution to the prediction of eddy trajectory, and the protection of ocean environment.

关键词： Mesoscale eddies Eddy propagation Eddy meridional deflection Satellite observation geostrophic adjustment

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地形对地转适应和锋生的影响(英文)

Advances in Atmospheric Sciences 2001年第4期18卷 524-538页

作者：方娟伍荣生 The Key Laboratory of Mesoscale Sever Weather (MOE) Nanjing University Nanjing

Three conservative principles: potential vorticity, absolute momentum and potential temperature are used to study the influence of topography on the local frontogenesis and geostrophic adjustment, which are induced by the inhomogeneous thermal fields. It is found that the horizontal distribution of the initial potential temperature and its position relative to the mountain play important roles during the geostrophic adjustment and local frontogenesis. The frontogenesis is weakened by the mountain when the initial thermal perturbation is located at the base of the upwind slope. The frontal discontinuity cannot occur unless the horizontal contrast of the initial potential temperature is great enough. Whereas, the situation is opposite when the initial thermal disturbance is main-ly situated near the peak of the mountain. Complementary to the aforementioned cases, the effect of topog-raphy on the frontogenesis depends on the stratification of the flow when the initial thermal disturbance lies at the foot of lee slope. For weak stratification, topography is favorable to the formation of frontal discontinuity, vice versa. This discrepancy is attributed to the difference of subsidence warming, caused by the mountain, when the stratification is either strong or weak. Furthermore, the energy conversion ratio between the kinetic and potential energy during the geostrophic adjustment process is also affected by the topography. In contrast to the flat bottom case, the ratio is reduced (increased) when the initial thermal perturbation lies in the up-wind slope (lee slope). The reason is that the gravity force does negative work in the former case while does positive work in the latter case. Key words Topography - geostrophic adjustment - Frontogenesis This work was supported by the National Natural Science Foundation of China under Grant 49735180, and by the State Key Basic Program: CHERES.

关键词： Topography geostrophic adjustment Frontogenesis

A Survey of Unbalanced Flow Diagnostics and Their Application

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Advances in Atmospheric Sciences 2000年第2期17卷 165-183页

作者： Fuqing Zhang Steven E. Koch Christopher A. Davis and Michael L. Kaplan Department of Marine Earth and Atmospheric Sciences North Carolina State University Raleigh USA National Center for Atmospheric Research Boulder USA

This paper presents an extensive survey of the most commonly used tools for diagnosing unbalanced flow in the atmosphere, namely the Lagrangian Rossby number, Psi vector, divergence equation, nonlinear balance equation, generalized omega-equation, and departure from fields obtained by potential vorticity (PV) inversion. The basic thoery, assumptions as well as implementation and limitations for each of the tools are all discussed. These tools are applied to high—resolution mesoscale model data to assess the role of unbalanced dynamics in the generation of a mesoscale gravity wave event over the East Coast of the United States. Comparison of these tools in this case study shows that these various methods agree to a large extent with each other though they differ in details. Key words Unbalanced flow - geostrophic adjustment - Gravity waves - Nonlinear balance equation - Potential vorticity inversion - Omega equations - Rossby number This research was conducted under support from NSF grant ATM-9700626 of the United States. The numerical computations described herein were performed on the Cray T90 at the North Carolina Supercomputing Center and the Cray supercomputer at the NCAR Scientific Computing Division, which also provided the initialization fields for the MM5. Thanks are extended to Mark Stoelinga at University of Washington for the RIP post-processing package.

关键词： Unbalanced flow geostrophic adjustment Gravity waves Nonlinear balance equation Potential vorticity inversion Omega equations Rossby number

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平衡流形成的机制与锋生(英文)

Advances in Atmospheric Sciences 2001年第3期18卷 323-334页

作者：伍荣生方娟 Lab. of Mesoscale Severe Weather Nanjing University Nanjing 210093 China

The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the initial conditions. If the initial potential vortcity of the flow is non-uniform, the final state is not necessarily geostrophic. However, for the zero and uniform potential vorticity flow, the final state will satisfy the thermal wind relation when the length scale of the initial disturbance is large enough. Otherwise, discontinuity will occur in the geostrophic solution. In this case, the final balanced state will not be geostrophic any longer and an extended momentum coordinate is introduced to overcome the mult-value problem. Key words Frontogenesis - geostrophic adjustment - Thermal wind balance - Extended momentum coordinates The work was supported by the National Natural Science Foundation of China (Grant Nos. 49735180 and 40075011) and the State Key Basic Program: CHERES.

关键词： Frontogenesis geostrophic adjustment Thermal wind balance Extended momentum coordinates