Hydrostatic Simulations Research Articles

Shell nacre ultrastructure and depressurisation dissolution in the deep-sea hydrothermal vent mussel Bathymodiolus azoricus

This study describes the micro-morphological features of the shell nacre in the vent mytilid Bathymodiolus azoricus collected along a bathymetric gradient of deep-sea hydrothermal vents of the mid-Atlantic ridge (MAR). Pressure-dependent crystallisation patterns were detected in animals subjected to post-capture hydrostatic simulations. We provide evidence for the following: (1) shell micro morphology in B. azoricus is similar to that of several vent and cold-seep species, but the prismatic shell layers may vary among bathymodiolids; (2) nacre micro-morphology of mussels from three vent sites of the MAR did not differ significantly; minor differences do not appear to be related to hydrostatic pressure, but rather to calcium ion availability; (3) decompression stress may cause drop off in pH of the pallial fluid that damages nascent crystals, and in a more advanced phase, the aragonite tablets as well as the continuous layer of mature nacre; and (4) adverse effects of decompression on calcium salt deposition in shells was diminished by re-pressurisation of specimens. The implications of the putative influence of hydrostatic pressure on biomineralisation processes in molluscs are discussed.

The clymeniid dilemma: functional implications of the dorsal siphuncle in clymeniid ammonoids

Clymeniid ammonoids appeared during the Late Devonian (Mid-Famennian) and quickly radiated before becoming extinct at the Devonian/Carboniferous boundary. Outwardly indistinguishable from other ammonoids, clymeniids are distinguished internally by their dorsal siphuncle, contrasted to a ventral siphuncle in almost all other ammonoids. Comparisons of a sample of Clymeniida (n = 22 genera), Goniatitida (n = 33), Prolecanitida (n = 12), and Anarcestida (n = 13) indicate that clymeniids fall within the range of other ammonoids in terms of shell geometry and suture complexity, but their siphuncles average two to three times larger and clymeniid shells are approximately 33% thicker than those of other ammonoids. Although a dorsal siphuncle would be about 50% smaller in surface area and volume than if located in a ventral position, the enlarged clymeniid siphuncle partially and, in some cases, fully compensated for this loss. Hydrostatic simulations of 15 clymeniid genera indicate that their thicker (therefore heavier) shells would have resulted in relatively short body chambers (≈280°) and high aperture orientations (≈90°). In static life-position, these orientations would have placed the dorsal clymeniid siphuncle at or near the bottom of the most recently formed chambers, seemingly an ideal location for draining liquid from the chamber. Migration of the siphuncle to the dorsal side of the shell occurs suddenly during early ontogeny (within the first two or three chambers), and mutation of homeotic gene expression is offered as a possible explanation for the sudden shift. A dorsal siphuncle may have resulted in selection for enlarged siphuncles, but this may have incurred loss of strength against hydrostatic pressure (thereby reducing depth limits) and thus rendered the clade more susceptible to the multiple eustatic and anoxic events that marked the end of the Devonian.

An Analysis of the Nonhydrostatic Dynamics in Numerically Simulated Antarctic Katabatic Flows*

Abstract A series of two-dimensional numerical experiments was conducted in order to describe the role of nonhydrostatic dynamics in simple Antarctic katabatic flows. The results presented include a comparison of the thermodynamic and dynamic fields produced by hydrostatic and nonhydrostatic numerical simulations. The source of the differences in the simulations was diagnosed based on an analysis of the model equation tendencies as well as calculated components of the pressure gradient force. Over most of the terrain slope, the nonhydrostatic effects were found to be insensitive to the model horizontal resolution, for a grid spacing ranging from 5 to 100 km.

Stability of a Cold Core Eddy in the Presence of Convection: Hydrostatic versus Nonhydrostatic Modeling

Geostrophic eddies in a stratified liquid are susceptible to baroclinic instabilities. In this paper, the authors consider these instabilities when such an eddy is simultaneously cooled homogeneously from above. As a linear stability analysis shows, the developing convection modifies the background stratification, the stability boundaries, and the patterns of the dominant modes. The coupling between the effects of convection and the largescale flow development of the eddy is studied through high-resolution numerical simulations, using both nonhydrostatic and hydrostatic models. In the latter models, several forms of convective adjustment are used to model convection. Both types of models confirm the development of the dominant modes and indicate that their nonlinear interaction leads to localized intense convection. By comparing nonhydrostatic and hydrostatic simulations of the flow development carefully, it is shown that convective adjustment may lead to erroneous smallscale variability. A simple alternative formulation of convective adjustment is able to give a substantial improvement.

1993年8月6日に起こった鹿児島豪雨を対象とした静水圧モデルと非静水圧モデルとの比較実験

Comparative experiments with real data using hydrostatic and non-hydrostatic models are performed for the torrential rain which occurred on 6 August 1993 in Kagoshima, the southern Kyushu, Japan. A modified version of the three-dimensional anelastic model (Saito, 1994; Kato and Saito, 1995) is used, which is nested with the operational hydrostatic model (the Japan Spectral Model) of the Japan Meteorological Agency. An explicit warm rain process predicting cloud water and rainwater and the moist convective adjustment are individually or conjunctionally employed in the model. The non-hydrostatic simulations of 5 and 10 km horizontal-resolution with a warm rain scheme reproduce continuously heavy rain which corresponds well with the observation. As Kato and Saito (1995) pointed out in a previous comparative experiment of ideal moist convection, the hydrostatic simulation tends to overestimate and overexpand precipitation in comparison with the non-hydrostatic counterpart, and the drag effect of hydrostatic water loading is more significant for convective development than the non-hydrostatic effect. Furthermore, in the 5 km simulations, the hydrostatic approximation greatly overestimates the total precipitation, more than in the simulation of ideal moist convection (Kato and Saito, 1995). From these results, a non-hydrostatic model with hydrostatic water loading is recommended for a high-resolution numerical prediction model.

Meso‐β‐scale circulations in realistic fronts. I: Steady basic state

AbstractThis paper investigates the occurrence of conditional symmetric instability during MFDP/Fronts87IOP2. A saturated negative equivalent‐potential‐vorticity area is detected by the mesoscale analysis in the upper troposphere, and this is confirmed by dropsounding data. Two‐dimensional hydrostatic simulations are performed with the Météo‐France PERIDOT model which give rise to the onset of symmetric instability. A complete life cycle is obtained as well as the growth rate of the perturbation (about 2.5 × 10−5 s−1 ≈ (11 hours)−1). Particular emphasis is put on the meanings and results of the kinetic‐energy conversions. Most of the perturbation energy comes from the basic state through vertical momentum fluxes, which is consistent with previous theoretical or numerical works. the decay of the perturbation is also shown to be due to its own dynamics, the symmetric rolls advecting positive equivalent potential vorticity into the unstable region. Deformations of equivalent potential temperature (θe) surfaces and m‐surfaces give an insight into the parcel trajectories: the ascending parcels follow θe‐surfaces. leading to a buckling of the m‐surfaces, and the descending parcels follow θ‐surfaces. the small value of the growth rate is stressed as well as of the maximum intensity (w ≈ 5 cm s−1). Thus, interactions with the frontogenetical forcing are expected owing to the small growth rate obtained. This is the subject of Part II of this paper.

A model investigation of summertime diurnal ozone behavior in rural mountainous locations

The STEM-II pollutant transport, transformation, and deposition model has been used to simulate diurnal patterns of surface ozone concentration at idealized high-elevation mountaintop locations and low-elevation plains and valley sites. Two-dimensional hydrostatic mesoscale simulations, initialized with atmospheric conditions representative of sunrise over the southern Appalachians on 19 June, were used to generate meteorological data to drive STEM-II simulations. Sensitivity of surface ozone concentrations has been investigated against input initial and background vertical profiles, synoptic wind speed, photochemistry, and surface removal. The model reproduced typical surface ozone concentration diurnal patterns observed at several high- and low-elevation sites in the United States and central Europe. Results indicate that the nighttime high ozone concentrations at high-elevation mountainous locations are primarily due to the occurrence of local topographically induced wind systems which transport ozone-rich air from aloft down mountain slopes. The simulations indicate that in some situations higher ozone concentrations may also be observed at mountaintop locations due to transport of residual ozone-rich air masses above the nocturnal boundary layer to high-elevation locations.

湿潤対流をシミュレートする場合の静水圧モデルと非静水圧モデルとの比較実験

Comparative experiments of moist convection using hydrostatic and non-hydrostatic models are performed to study the suitability of the hydrostatic approximation for a high-resolution model when the grid size falls below 20km. The moist convection in the models is treated by the use of an explicit warm-rain process predicting cloud water and rainwater as well as by a semi-explicit scheme consisting of the warm-rain process and moist convective adjustment. The differences between the experiments with and without hydrostatic water loading are also examined and quantitatively compared with those between the hydrostatic and non-hydrostatic simulations.When the prognostic explicit scheme is used, the hydrostatic simulation overdevelops moist convection, overestimates the total amount of precipitation, and overexpands the area of precipitation as the grid size decreases. This overdevelopment alters substantially the structure of moist convection and precipitation patterns. The absence of hydrostatic water loading also alters the total amount and structure of precipitation. Hydrostatic water loading exerts more significant influences on simulated precipitation than the hydrostatic approximation. In the 20-km simulations, the hydrostatic simulation with hydrostatic water loading produces results that are comparable to the non-hydrostatic counterpart.The difference in the total amount of precipitation between the hydrostatic and non-hydrostatic simulations was not as large as that of the convective development. This can be explained by considering the total water budget, which includes simulated precipitation and water vapor flux through the lateral boundaries, i. e., the water-vapor flux in the hydrostatic simulation corresponds to that in the non-hydrostatic one.Although moist convective adjustment removes conditional instability and does not produce strong updrafts, the characteristics of the results in the comparative experiments of moist convection using hydro-static and non-hydrostatic models were hardly changed by the incorporation of moist convective adjustment (the semi-explicit scheme). On the other hand, hydrostatic water loading exerts more significant influences on simulated precipitation with the semi-explicit scheme than that with the prognostic explicit scheme. Therefore, in developing 10-20km numerical weather prediction models, hydrostatic water loading should be evaluated in preference to adopting non-hydrostatic models.

Technical summary of the Naval Air Warfare Center (NAWC)−Open Water Facility (OWF)

The NAWC-OWF is a Navy-owned facility dedicated to the development and measurement of sonobuoy transducers. It is located at a flooded quarry in Pennsylvania about 30 mi north of Philadelphia. Measurements are performed from a laboratory barge where the water depth is 60 ft and the nearest wall is 180 ft away. Acoustic and mechanical measurements consist of: (a) transmitting and receiving responses, (b) directivity patterns, (c) impedance and admittance, (d) hydrostatic simulation up to 8000 psig, (e) flow simulation from 0.1 to 1.0 kn using a 100-ft I beam rail, (f) first-order sea-state simulations up to sea state five, and (g) lift and drag with 18 data channels. Data are obtained via hard wire or rf link. The low-frequency cutoff is 200 Hz for pulse measurements and 3 Hz for continuous wave (CW) measurements. Instrumentation is controlled with menu-driven software and data outputs are real time in paper, disk, or tape format. The facility weight limits, in water, are 500 lbs for acoustic data and 100 lbs for mechanical data. The facility has phone and FAX service and a photo copy machine.

Meso-beta scale numerical simulations of terrain drag-induced along-stream circulations. Part II: Concentration of potential vorticity within dryline bulges

Hydrostatic and nonhydrostatic simulation models are employed to study the intensification of a terrain drag-induced dryline. The study develops a multi-stage theory for the evolution of the dryline including the concentration of potential vorticity accompanying meso-gamma scale dryline “bulges”.

Pressure drag and momentum fluxes due to the Alps. II: Representation in large‐scale atmospheric models

AbstractA three‐dimensional numerical model with interactive grid nesting is used to study the pressure drag and associated momentum fluxes due to the Alpine complex (for a specified upstream wind and static stability profile). Four basic questions are addressed which are relevant to the problems of flow description in the vicinity of mountains and the impact of orography in the context of mesoscale numerical weather prediction and general circulation models: What is the dependence of basic quantities such as the pressure drag on the model's horizontal resolution? Is there a need for non‐hydrostatic dynamics to account properly for the flow characteristics near steep mountains? Is there an effective role for enhanced orography such as an envelope formulation? Might a ‘gravity‐wave‐drag’ parametrization scheme be able to represent adequately the highest resolution fluxes and surface drag in a much coarser resolution model? A series of experiments with both hydrostatic and non‐hydrostatic models at resolutions of 80, 40, 20, 10 and 5 km is analysed, and two of these experiments are repeated with an envelope orography.It is concluded that hydrostatic simulations are sufficient to describe the basic dynamics even at 5 km resolution; however, there is a strong dependence of the drag and momentum fluxes on resolution, with the drag at 80 km resolution being almost half that at the highest resolution. It is also shown that the use of an envelope orography at coarser resolutions can compensate significantly for the drag under‐estimation, but is less effective in representing the vertical stress profiles or the direction of the stress vectors, which are systematically in error at the coarsest resolution. The potential role of gravity wave drag is confirmed and possible improvements considered. It is suggested that both envelope orography and gravity wave drag may make a significant contribution until resolutions are as high as 10 to 20 km.

Pressure drag and momentum fluxes due to the Alps. II: Representation in large-scale atmospheric models

A three-dimensional numerical model with interactive grid nesting is used to study the pressure drag and associated momentum fluxes due to the Alpine complex (for a specified upstream wind and static stability profile). Four basic questions are addressed which are relevant to the problems of flow description in the vicinity of mountains and the impact of orography in the context of mesoscale numerical weather prediction and general circulation models: (i) What is the dependence of basic quantities such as the pressure drag on the model's horizontal resolution? (ii) Is there a need for non-hydrostatic dynamics to account properly for the flow characteristics near steep mountains? (iii) Is there an effective role for enhanced orography such as an envelope formulation? (iv) Might a ‘gravity-wave-drag’ parametrization scheme be able to represent adequately the highest resolution fluxes and surface drag in a much coarser resolution model? A series of experiments with both hydrostatic and non-hydrostatic models at resolutions of 80, 40, 20, 10 and 5 km is analysed, and two of these experiments are repeated with an envelope orography. It is concluded that hydrostatic simulations are sufficient to describe the basic dynamics even at 5 km resolution; however, there is a strong dependence of the drag and momentum fluxes on resolution, with the drag at 80 km resolution being almost half that at the highest resolution. It is also shown that the use of an envelope orography at coarser resolutions can compensate significantly for the drag under-estimation, but is less effective in representing the vertical stress profiles or the direction of the stress vectors, which are systematically in error at the coarsest resolution. The potential role of gravity wave drag is confirmed and possible improvements considered. It is suggested that both envelope orography and gravity wave drag may make a significant contribution until resolutions are as high as 10 to 20 km.

A comparison between hydrostatic and nonhydrostatic simulations of gravity currents and their interaction with orography

The implications of the hydrostatic assumption for an anelastic two-dimensional numerical model of a gravity current intruding into a neutrally stratified environment are studied. Particular interest is focused on situations where the gravity current encounters an orographic barrier. Considerable discrepancies between hydrostatic and nonhydrostatic calculations are found in the head region for high Froude numbers, when the resolution is high enough to resolve the head of the current. However, the propagation speed and the depth of the feeder flow are well represented in the hydrostatic model.

Product Temperature Prediction in Hydrostatic Retorts

ABSTRACT A computer model, based on Fourier's law of heat conduction with a time-dependent boundary condition, was developed to predict the time-temperature profile at the center of a canned food processed in a hydrostatic retort. The effects, on product cooling, of various temperature/pressure events characteristic of the exit hydrostatic leg were studied by performing hydrostatic simulations. Water temperatures of 130 F, 160 F, and 190 F (54.4, 71.1 and 87.8 C) were compared in combination with (a) the 15 psig (0.72 kPa) to 0 psig (0 kPa) gradient imposed by a 39 foot (11.9 m) high exit water leg and (b) a static pressure of 15 psig (0.72 kPa). The model closely predicted product temperatures during the initial portion of the hydrostatic leg (gradient pressure) residence but temperature predictions associated with subsequent cooling were less precise. When an artificially constant overriding pressure was maintained, predicted temperatures were consistently in good agreement with those measured experimentally. This evidence suggests that external pressure-related changes in headspace volume induce convection effects that are not accounted for by the conduction model.