Hydrostatic Pressure Perturbation Research Articles

Ice-shelf vibrations modeled by a full 3-D elastic model

ABSTRACTForced ice-shelf vibration modeling is performed using a full 3-D finite-difference elastic model, which also takes into account sub-ice seawater flow. The sea water flow is described by the wave equation. Ice-shelf flexure therefore results from hydrostatic pressure perturbations in the sub-ice seawater layer. Numerical experiments were undertaken for idealized rectangular ice-shelf geometry. The ice-plate vibrations were modeled for harmonic incoming pressure perturbations and for a wide range of incoming wave frequencies. The spectra showed distinct resonant peaks, which demonstrate the ability of the model to simulate a resonant-like motion. The spectra obtained by the full 3-D model are compared with exact solutions for the elastic thin plate with two fixed edges and two free edges. The spectra are also compared with the spectra modeled by the thin-plate Holdsworth and Glynn model (1978).

The Eigen Value Problem for Ice-Tongue Vibrations in 3-D and Thin-Plate Elastic Models

The Eigen Value Problem for Ice-Tongue Vibrations in 3-D and Thin-Plate Elastic Models Y. V. Konovalov Abstract Ice tongue forced vibration modeling is performed using a full 3D finite-difference elastic model, which also takes into account sub-ice seawater flow. The ocean flow in the cavity is described by the wave equation, therefore ice tongue flexures result from hydrostatic pressure perturbations in sub-ice seawater layer. Numerical experiments have been carried out for idealized rectangular and trapezoidal ice-shelf geometries. The ice-plate vibrations are modeled for harmonic in-going pressure perturbations and for high-frequency wave spectra of ocean swell. The spectra show distinct resonance peaks, which demonstrate the ability to model a resonant-like motion in the suitable conditions of forcing. The spectra and ice tongue deformations obtained by the developed full 3D model are compared with the spectra and the deformations modeled by the thin-plate Holds worth and Glynn model (1978). The main resonance peaks and ice tongue deformations in the corresponding modes, derived by the full 3D model, are in agreement with the peaks and deformations obtained by the Holds worth and Glynn model for relatively high aspect ratio (λ≥ 0.03). The relative deviation between the Eigen values (periodicities) in the two compared models is about 10%. Full Text: PDF DOI: 10.15640/jges.v4n2a5

Transient Growth of Thermodynamically Coupled Variations in the Tropics under an Equatorially Symmetric Mean State*

Abstract The dynamics of thermodynamically coupled disturbances in the tropics that bear a strong resemblance to observed meridional mode variations are investigated using two simple linear coupled models. Both models involve an ocean equation coupled to the atmosphere via the linearized effect of zonal wind variations on the surface bulk latent heat flux. The two models differ in their atmospheric components, which consist of (i) a Gill–Matsuno style model of the free troposphere in which atmospheric heating is parameterized to be linearly proportional to sea surface temperature and (ii) a reduced-gravity model of the tropical boundary layer in which SST anomalies are associated with hydrostatic pressure perturbations throughout the boundary layer. Both atmospheric models follow the standard shallow-water equations on an equatorial beta plane. Growth rates and propagation of coupled disturbances are calculated and diagnosed via eigenanalysis of the linear models and singular value decomposition of the Green’s function for each model. It is found that the eigenvectors of either model are all damped, not orthogonal, and not particularly meaningful in understanding observed tropical coupled variability. The nonnormality of the system, however, leads to transient growth over a time period of about 100 days (based on the choice of parameters in this study). The idealized initial and final conditions that experience this transient growth resemble observed tropical meridional mode variations and tend to propagate equatorward and westward in accord with findings from previous theoretical and modeling studies. Instantaneous growth rates and propagation characteristics of idealized transient disturbances are diagnosed via the linearized atmospheric potential vorticity equation and via propagation characteristics of atmospheric equatorial Rossby waves. Constraints on the poleward extent of initial conditions or imposed steady forcing that can lead to tropical meridional mode variations are identified through analysis of the steady coupled equations. Three constraints limit the poleward extent of forcing that can generate tropical meridional mode variations: (i) a dynamical constraint imposed by the damping rate of the temperature equation as well as the propagation speed of the mode along its wave characteristic; (ii) a constraint imposed by the effectiveness of zonal wind variations in generating surface latent heat flux anomalies; and (iii) the surface moisture convergence, which limits the poleward extent and strength of ocean to atmosphere coupling.

Energetics of the Global Ocean: The Role of Layer-Thickness Form Drag

Abstract Understanding the role of mesoscale eddies in the global ocean is fundamental to gaining insight into the factors that control the strength of the circulation. This paper presents results of an analysis of a high-resolution numerical simulation. In particular, the authors perform an analysis of energetics in density space. Such an approach clearly demonstrates the role of layer-thickness form drag (residual effects of hydrostatic pressure perturbations), which is hidden in the classical analysis of the energetics of flows. For the first time in oceanic studies, the global distribution of layer-thickness form drag is determined. This study provides direct evidence to verify some basic characteristics of layer-thickness form drag that have often been assumed or speculated about in previous theoretical studies. The results justify most of the previous assumptions and speculations, including those associated with (i) the presence of an oceanic energy cycle explaining the relationship between layer-thickness form drag and wind forcing, (ii) the manner in which layer-thickness form drag removes the energy of vertically sheared geostrophic currents, and (iii) the reason why the work of layer-thickness form drag nearly balances the work of eddy-induced overturning circulation in each vertical column. However, the result of the analysis disagrees with speculation in previous studies that the layer-thickness form drag in the Antarctic Circumpolar Current is the agent that transfers the wind-induced momentum near the sea surface downward to the bottom layers. The authors present a new interpretation: the layer-thickness form drag reduces (and thereby cancels) the vertical shear resulting from the eddy-induced overturning circulation (rather than the vertical shear resulting from the surface wind stress). This interpretation is consistent with the results of the energy analysis conducted in this study.

The trailing-edge problem for mixed-convection flow past a horizontal plate

The flow near the trailing edge of a horizontal plate in a uniform parallel stream under a small angle of attack in the limit of large Reynolds number and large Grashof number is considered. Applying the concept of interacting boundary layers, a triple-deck problem taking the hydrostatic pressure perturbation into account can be formulated. However, it turns out that the interaction pressure is discontinuous at the trailing edge and thus new sublayers to resolve the discontinuity are introduced.

Conformational heterogeneity of cytochrome P450 3A4 revealed by high pressure spectroscopy

We applied hydrostatic pressure perturbation to study substrate-induced transitions in human cytochrome P450 3A4 (CYP3A4) with bromocriptine (BCT) as a substrate. The barotropic behavior of the purified enzyme in solution was compared with that observed in recombinant microsomes of Saccharomyces cerevisiae coexpressing CYP3A4, cytochrome b 5, ( b 5) and NADPH-cytochrome P450 reductase (CPR). Important barotropic heterogeneity of CYP3A4 was detected in both cases. Only about 70% of CYP3A4 in solution and about 50% of the microsomal enzyme were susceptible to a pressure-induced P450 → P420 transition. The results suggest that both in solution and in the membrane CYP3A4 is represented by two conformers with different positions of spin equilibrium and different barotropic properties. No interconversion between these conformers was observed within the time frame of the experiment. Importantly, a pressure-induced spin shift, which is characteristic of all cytochromes P450 studied to date, was detected in CYP3A4 in solution only; the P450 → P420 transition was the sole pressure-induced process detected in microsomes. This fact suggests unusual stabilization of the high-spin state of CYP3A4, which is assumed to reflect decreased water accessibility of the heme moiety due to specific interactions of the hemoprotein with the protein partners ( b 5 and CPR) and/or membrane lipids.

Thermal stability of intrinsic stress birefringence in optical fibers

Through Duhamel's analogy in thermoelasticity, the condition of zero temperature fluctuation of intrinsic stress birefringence is derived. The condition requires the regions bordering the nonaxisymmetric interfaces in the fiber cross-section to have identical thermoelastic properties but different fictive temperatures. It is found that thermal instability of birefringence is predominantly caused by the mismatch in expansion coefficients between these regions. The condition may be incorporated into most fibers during performance preparation, whether silica based or not. Birefringent fibers satisfying this condition will also have intrinsic stress birefringence stabilized against hydrostatic-pressure perturbation on the surface as well as uniform axial tension at the ends, regardless of coating properties.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Method to Determine Nonhydrostatic Effects within Subdomains in a Mesoscale Model

Abstract The exact solution of the nonhydrostatic pressure residual (total pressure perturbation minus hydrostatic pressure perturbation) in Defant's linear model is derived. The quasi-nonhydrostatic residual, introduced by Pielke, and the pressure-correction term by Orlanski are compared with the exact residual for varying physical situations. It is found that, within the linear framework, nonhydrostatic effects generally become relatively more important when the environmental stability is near the neutral state and/or the associated horizontal length scale is several kilometers or smaller. The residual components associated with buoyancy and horizontal momentum are the two important physical mechanisms contributing to the generation of nonhydrostatic effects. In a near-neutral environment, a pressure residual must include the horizontal momentum nonhydrostatic residual in order to approximate more accurately the nonhydrostatic effects, while in a sufficiently stable environment the total pressure tends ...

Effects of the Pressure Perturbation Field in Numerical Models of Unidirectionally Sheared Thunderstorm Convection: Two versus Three Dimensions

The physical roles of 'buoyant' and 'dynamic' pressure components, and the distinction between buoyant and hydrostatic pressure perturbations, are aspects of the pressure perturbation field in strongly sheared convective storms studied by means of two- and three-dimensional anelastic numerical modeling experiments with common environmental profiles. The pressure analysis clarifies the differences between two- and three-dimensional storms. In the main updraft, strong midlevel thermal buoyancy is partly opposed by a downward-perturbed vertical pressure gradient force. This, however, occurs to a much greater extent in two dimensions than in three, contributing to smaller net upward accelerations. While the buoyant and hydrostatic fields are intimately related to the total buoyancy distribution, the buoyant pressure perturbation is smoother and of lower amplitude than its hydrostatic counterpart. For the model experiments, this distinction is far greater in three dimensions than in two, in association with the smaller scale of the active convection in three dimensions.