scholarly journals Stability Analysis of Geostrophic Adjustment on Hexagonal Grids for Regions with Variable Depth

2005 ◽  
Vol 133 (11) ◽  
pp. 3335-3344 ◽  
Author(s):  
Tomas Torsvik ◽  
Øyvind Thiem ◽  
Jarle Berntsen
Keyword(s):  
Ocean Circulation ◽  
Numerical Solutions ◽  
Ocean Basin ◽  
Paper Analysis ◽  
Variable Depth ◽  
Atmospheric Models ◽  
Numerical Studies ◽  
Energy Conserving ◽  
Hexagonal Grids ◽  
Ocean Models

Abstract Hexagonal grids have been used in a number of numerical studies, and especially in relation to atmospheric models. Recent studies have suggested that ocean circulation models may also benefit from the use of hexagonal grids. These grids tend to induce less systematic errors and have better horizontal isotropy properties than traditional square grid schemes. If hexagonal grids are to be applied in ocean models, a number of features that are characteristic of ocean circulation problems need to be attended to. The topography of the ocean basin is an important feature in most ocean models. Ocean modelers can experience instabilities due to depth variations. In the present paper, analysis of the propagation matrix for the spatially discretized system is used to explain unphysical growth of the numerical solutions of the linear shallow water equations when using hexagonal grids over domains with variable depth. It is shown that a suitable weighting of the Coriolis terms may give an energy-conserving and stable numerical scheme.

scholarly journals Kinetic energy-conserving hyperdiffusion can improve low resolution atmospheric models

2015 ◽  
Vol 7 (3) ◽  
pp. 1117-1135 ◽  
Author(s):  
Pablo Zurita-Gotor ◽  
Isaac M. Held ◽  
Malte F. Jansen
Keyword(s):  
Kinetic Energy ◽  
Atmospheric Models ◽  
Low Resolution ◽  
Energy Conserving

scholarly journals Gravity currents and internal waves in a stratified fluid

2008 ◽  
Vol 616 ◽  
pp. 327-356 ◽  
Author(s):  
BRIAN L. WHITE ◽  
KARL R. HELFRICH
Keyword(s):  
Internal Waves ◽  
Wave Speed ◽  
Numerical Solutions ◽  
Gravity Current ◽  
Gravity Currents ◽  
Stratified Fluid ◽  
Front Speed ◽  
Long Wave ◽  
Conjugate State ◽  
Energy Conserving

A steady theory is presented for gravity currents propagating with constant speed into a stratified fluid with a general density profile. Solution curves for front speed versus height have an energy-conserving upper bound (the conjugate state) and a lower bound marked by the onset of upstream influence. The conjugate state is the largest-amplitude nonlinear internal wave supported by the ambient stratification, and in the limit of weak stratification approaches Benjamin's energy-conserving gravity current solution. When the front speed becomes critical with respect to linear long waves generated above the current, steady solutions cannot be calculated, implying upstream influence. For non-uniform stratification, the critical long-wave speed exceeds the ambient long-wave speed, and the critical-Froude-number condition appropriate for uniform stratification must be generalized. The theoretical results demonstrate a clear connection between internal waves and gravity currents. The steady theory is also compared with non-hydrostatic numerical solutions of the full lock release initial-value problem. Some solutions resemble classic gravity currents with no upstream disturbance, but others show long internal waves propagating ahead of the gravity current. Wave generation generally occurs when the stratification and current speed are such that the steady gravity current theory fails. Thus the steady theory is consistent with the occurrence of either wave-generating or steady gravity solutions to the dam-break problem. When the available potential energy of the dam is large enough, the numerical simulations approach the energy-conserving conjugate state. Existing laboratory experiments for intrusions and gravity currents produced by full-depth lock exchange flows over a range of stratification profiles show excellent agreement with the conjugate state solutions.

The geography of numerical mixing in a suite of global ocean models

2021 ◽  
Author(s):  
Ryan Holmes ◽  
Jan Zika ◽  
Stephen Griffies ◽  
Andrew Hogg ◽  
Andrew Kiss ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Horizontal Resolution ◽  
Global Ocean ◽  
Vertical Diffusivity ◽  
Mixing Parameters ◽  
Ocean Models ◽  
Numerical Mixing ◽  
Comparable Magnitude ◽  
Ice Model

<p>Numerical mixing, the physically spurious diffusion of tracers due to the numerical discretization of advection, is known to contribute to biases in ocean circulation models. However, quantifying numerical mixing is non-trivial, with most studies utilizing specifically targeted experiments in idealized settings. Here, we present a precise method based on water-mass transformation for quantifying numerical mixing, including its spatial structure, that can be applied to any conserved variable in global general circulation ocean models. The method is applied to a suite of global MOM5 ocean-sea ice model simulations with differing grid spacings and sub-grid scale parameterizations. In all configurations numerical mixing drives across-isotherm heat transport of comparable magnitude to that associated with explicitly-parameterized mixing. Numerical mixing is prominent at warm temperatures in the tropical thermocline, where it is sensitive to the vertical diffusivity and resolution. At colder temperatures, numerical mixing is sensitive to the presence of explicit neutral diffusion, suggesting that much of the numerical mixing in these regions acts as a proxy for neutral diffusion when it is explicitly absent. Comparison of equivalent (with respect to vertical resolution and explicit mixing parameters) 1/4-degree and 1/10-degree horizontal resolution configurations shows only a modest enhancement in numerical mixing at the eddy-permitting 1/4-degree resolution. Our results provide a detailed view of numerical mixing in ocean models and pave the way for future improvements in numerical methods.</p>

scholarly journals Assymmetric eddy populations in adjacent basins – a high resolution numerical study of the Tyrrhenian and Ligurian Seas

2012 ◽  
Vol 9 (6) ◽  
pp. 3521-3566 ◽  
Author(s):  
R. M. A. Caldeira ◽  
X. Couvelard ◽  
E. Casella ◽  
A. Vetrano
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Mesoscale Eddy ◽  
Leeward Side ◽  
Boundary Current ◽  
High Concentration ◽  
Eddy Activity ◽  
Tyrrhenian Basin

Abstract. A high-resolution ocean circulation modelling system forced with a high-resolution numerical wind product was used to study the mesoscale and sub-mesoscale eddy population of the North-Western Mediterranean Sea, contrasting eddy-activity between the Tyrrhenian and Ligurian sub-basins. Numerical solutions reproduced some of the known regional dynamics, namely the occurrence and oceanic implications of Mistral events, the convective cell leeward of the Gulf of Lion, as well as the Balearic frontal system. Calculated transport across the Corsica Channel followed a similar trend, when compared to the transport computed from a moored current meter. The analysis of the results showed that surface eddy activity is mostly confined to the boundary-currents, whereas in the deeper layers most eddies are concentrated on the central-deeper part of the basins. The Liguro-Provençal basin shows a much higher concentration of intermediate and deep-water eddies, when compared to the Tyrrhenian basin. Sub-mesoscale surface eddies tend to merge and migrate vertically onto intermediate waters. Intense eddy activity in the boundary-current surrounding the Liguro-Provençal Gyre, concentrate high-productivity, manifested by higher concentrations of mean sea surface chlorophyll, in the central part of the gyre, defined herein as the Ligurian Productive Pool (LPP). On average, the Tyrrhenian was mostly oligotrophic except for a small productive vortice in the south-eastern (leeward) side of Corsica. The transport in the Tyrrhenian Gyre, and across the basin is one order of magnitude higher than the transport calculated for the Liguro-Provençal basin. A high concentration of eddies in the passage between the Balearic Archipelago and Sardinia suggests retention and longer residence times of nutrient rich water in the "Ligurian pool", compared to a "fast draining" Tyrrhenian basin. Previous studies support the cyclonic gyre circulation generated in the Liguro-Provençal basin but more studies are needed to address the surface and deep mesoscale activity of the Tyrrhenian basin.

Representation of basal melting in idealised coupled ice sheet ocean models

2021 ◽  
Author(s):  
Chen Zhao ◽  
Rupert Gladstone ◽  
Ben Galton-Fenzi ◽  
David Gwyther
Keyword(s):  
Ocean Circulation ◽  
Critical Role ◽  
Ice Sheet ◽  
Ocean Model ◽  
Periodic Pattern ◽  
Regional Ocean Modeling System ◽  
Ice Shelf ◽  
Grounding Line ◽  
Ocean Models ◽  
Basal Melting

<p>The ocean-driven basal melting has important implications for the stability of ice shelves in Antarctic, which largely affects the ice sheet mass balance, ocean circulation, and subsequently global sea level rise. Due to the limited observations in the ice shelf cavities, the couple ice sheet ocean models have been playing a critical role in examining the processes governing basal melting. In this study we use the Framework for Ice Sheet-Ocean Coupling (FISOC) to couple the Elmer/Ice full-stokes ice sheet model and the Regional Ocean Modeling System (ROMS) ocean model to model ice shelf/ocean interactions for an idealised three-dimensional domain. Experiments followed the coupled ice sheet–ocean experiments under the first phase of the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP1). A periodic pattern in the simulated mean basal melting rates is found to be highly consistent with the maximum barotropic stream function and also the grounding line retreat row by row,  which is likely to be related with the gyre break down near the grounding line caused by some non-physical instability events from the ocean bottom. Sensitivity tests are carried out, showing that this periodic pattern is not sensitive to the choice of couple time intervals and horizontal eddy viscosities but sensitive to vertical resolution in the ocean model, the chosen critical water column thickness in the wet-dry scheme, and the tracer properties for the nudging dry cells at the ice-ocean interface boundary. Further simulations are necessary to better explain the mechanism involved in the couple ice-ocean system, which is very significant for its application on the realistic ice-ocean systems in polar regions.</p>

scholarly journals The Response of an Idealized Ocean Basin to Variable Buoyancy Forcing

2005 ◽  
Vol 35 (5) ◽  
pp. 601-615 ◽  
Author(s):  
M. A. Lucas ◽  
J. J. Hirschi ◽  
J. D. Stark ◽  
J. Marotzke
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean Basin ◽  
Meridional Overturning Circulation ◽  
Quasi Equilibrium ◽  
Vertical Diffusion ◽  
Strong Response ◽  
Buoyancy Forcing

Abstract The response of an idealized ocean basin to variable buoyancy forcing is examined. A general circulation model that employs a Gent–McWilliams mixing parameterization is forced by a zonally constant restoring surface temperature profile, which varies with latitude and time over a period P. In each experiment, 17 different values of P are studied, ranging from 6 months to 32 000 yr. The model's meridional overturning circulation (MOC) exhibits a very strong response on all time scales greater than 15 yr, up to and including the longest forcing time scales examined. The peak-to-peak values of the MOC oscillations reach up to 125% of the steady-state maximum MOC and exhibit resonance-like behavior, with a maximum at centennial to millennial forcing periods (depending on the vertical diffusivity). This resonance-like behavior stems from the existence of two adjustment time scales, one of which is set by the vertical diffusion and the other of which is set by the basin width. Furthermore, the linearity of the response as well as its lag with the forcing varies with the forcing period. The considerable deviation from the quasi-equilibrium response at all time scales above 15 yr is surprising and suggests a potentially important role of the ocean circulation for climate, even at Milankovich time scales.

scholarly journals The Deep Equatorial Ocean Circulation in Wind-Forced Numerical Solutions

2015 ◽  
Vol 45 (6) ◽  
pp. 1709-1734 ◽  
Author(s):  
François Ascani ◽  
Eric Firing ◽  
Julian P. McCreary ◽  
Peter Brandt ◽  
Richard J. Greatbatch
Keyword(s):  
Ocean Circulation ◽  
Numerical Solutions ◽  
Intraseasonal Variability ◽  
Low Frequency ◽  
Wind Forcing ◽  
Equatorial Atlantic ◽  
Vertical Scale ◽  
Equatorial Atlantic Ocean ◽  
High Vertical Resolution ◽  
Equatorial Ocean

AbstractWe perform eddy-resolving and high vertical resolution numerical simulations of the circulation in an idealized equatorial Atlantic Ocean in order to explore the formation of the deep equatorial circulation (DEC) in this basin. Unlike in previous studies, the deep equatorial intraseasonal variability (DEIV) that is believed to be the source of the DEC is generated internally by instabilities of the upper-ocean currents. Two main simulations are discussed: solution 1, configured with a rectangular basin and with wind forcing that is zonally and temporally uniform, and solution 2, with realistic coastlines and an annual cycle of wind forcing varying zonally. Somewhat surprisingly, solution 1 produces the more realistic DEC; the large, vertical-scale currents [equatorial intermediate currents (EICs)] are found over a large zonal portion of the basin, and the small, vertical-scale equatorial currents [equatorial deep jets (EDJs)] form low-frequency, quasi-resonant, baroclinic equatorial basin modes with phase propagating mostly downward, consistent with observations. This study demonstrates that both types of currents arise from the rectification of DEIV, consistent with previous theories. The authors also find that the EDJs contribute to maintaining the EICs, suggesting that the nonlinear energy transfer is more complex than previously thought. In solution 2, the DEC is unrealistically weak and less spatially coherent than in the first simulation probably because of its weaker DEIV. Using intermediate solutions, this study finds that the main reason for this weaker DEIV is the use of realistic coastlines in solution 2. It remains to be determined what needs to be modified or included to obtain a realistic DEC in the more realistic configuration.

scholarly journals Decadal predictability without ocean dynamics

2017 ◽  
Vol 114 (9) ◽  
pp. 2177-2182 ◽  
Author(s):  
Abhishekh Srivastava ◽  
Timothy DelSole
Keyword(s):  
Ocean Circulation ◽  
Climate Models ◽  
Internal Variability ◽  
Ocean Dynamics ◽  
Ocean Mixed Layer ◽  
Coupled Models ◽  
Linear Dynamics ◽  
Ocean Models ◽  
Slab Ocean ◽  
Decadal Predictability

This paper shows that the most predictable components of internal variability in coupled atmosphere–ocean models are remarkably similar to the most predictable components of climate models without interactive ocean dynamics (i.e., models whose ocean is represented by a 50-m-deep slab ocean mixed layer with no interactive currents). Furthermore, a linear regression model derived solely from dynamical model output can skillfully predict observed anomalies in these components at least a year or two in advance, indicating that these model-derived components and associated linear dynamics are realistic. These results suggest that interactive ocean circulation is not essential for the existence of multiyear predictability previously identified in coupled models and observations.

scholarly journals Mixing Inferred from an Ocean Climatology and Surface Fluxes

2017 ◽  
Vol 47 (3) ◽  
pp. 667-687 ◽  
Author(s):  
Sjoerd Groeskamp ◽  
Bernadette M. Sloyan ◽  
Jan D. Zika ◽  
Trevor J. McDougall
Keyword(s):  
Ocean Circulation ◽  
Climate Models ◽  
Eddy Diffusion ◽  
Surface Fluxes ◽  
Small Scale ◽  
Vertical Variation ◽  
Mixing Coefficient ◽  
Order Of Magnitude ◽  
Ocean Models ◽  
Isopycnal Mixing

AbstractThis study provides observation-based estimates, determined by inverse methods, of horizontal and isopycnal eddy diffusion coefficients KH and KI, respectively, the small-scale mixing coefficient D, and the diathermohaline streamfunction Ψ. The inverse solution of Ψ represents the ocean circulation in Absolute Salinity SA and Conservative Temperature Θ coordinates. The authors suggest that the observation-based estimate of Ψ will be useful for comparison with equivalent diagnostics from numerical climate models. The estimates of KH and KI represent horizontal eddy mixing in the mixed layer and isopycnal eddy mixing in the ocean interior, respectively. This study finds that the solution for D and KH are comparable to existing estimates. The solution for KI is one of the first observation-based global and full-depth constrained estimates of isopycnal mixing and indicates that KI is an order of magnitude smaller than KH. This suggests that there is a large vertical variation in the eddy mixing coefficient, which is generally not included in ocean models. With ocean models being very sensitive to the choice of isopycnal mixing, this result suggests that further investigation of the spatial structure of isopycnal eddy mixing from observations is required.

Numerical and Experimental Study on Welded and Bolted Steel Beam–Column Connections Subjected to Cyclic Loading

2017 ◽  
Vol 11 (04) ◽  
pp. 1750014
Author(s):  
Jinwon Shin ◽  
Jinkyu Kim
Keyword(s):  
Numerical Solutions ◽  
Steel Structures ◽  
Bolted Joints ◽  
Dissipated Energy ◽  
Steel Beam ◽  
Stress And Strain ◽  
Bolted Joint ◽  
Cyclic Tests ◽  
Local Responses ◽  
Numerical Studies

This paper presents experimental and numerical studies for predicting the seismic responses of welded and bolted steel beam–column connections, namely, welded unreinforced flange and bolted web connection, and welded unreinforced flange and welded web connection. Cyclic tests of these connections composed of members applied widely to steel structures are conducted to examine their seismic performance. Numerical simulations with a focus on the bolted joint are conducted using a nonlinear finite element code. Two different strategies of modeling bolted parts are provided to improve the computational efficiency of numerical analysis: solid contact elements and more simply using shell connector elements. Numerical solutions obtained for full connection models are experimentally validated. The rotational capacity and dissipated energy of the welded and bolted connections are discussed. The local responses for stress and strain in the vicinity of welded and bolted joints are also investigated.

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