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Journal articles on the topic 'Ageostrophic flow'

Author: Grafiati

Published: 4 June 2021

Last updated: 15 February 2022

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1

Brüggemann, Nils, and Carsten Eden. "Routes to Dissipation under Different Dynamical Conditions." Journal of Physical Oceanography 45, no. 8 (2015): 2149–68. http://dx.doi.org/10.1175/jpo-d-14-0205.1.

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AbstractIn this study, it is investigated how ageostrophic dynamics generate an energy flux toward smaller scales. Numerical simulations of baroclinic instability are used with varying dynamical conditions ranging from quasigeostrophic balance to ageostrophic flows. It turns out that dissipation at smaller scales by viscous friction is much more efficient if the flow is dominated by ageostrophic dynamics than in quasigeostrophic conditions. In the presence of ageostrophic dynamics, an energy flux toward smaller scales is observed while energy is transferred toward larger scales for quasigeostr

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2

Pallàs-Sanz, Enric, and Álvaro Viúdez. "Three-Dimensional Ageostrophic Motion in Mesoscale Vortex Dipoles." Journal of Physical Oceanography 37, no. 1 (2007): 84–105. http://dx.doi.org/10.1175/jpo2978.1.

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Abstract The three-dimensional motion of mesoscale baroclinic dipoles is simulated using a nonhydrostatic Boussinesq numerical model. The initial conditions are two ellipsoidal vortices of positive and negative potential vorticity anomalies. The flow is moderately ageostrophic with a maximum absolute Rossby number equal to 0.71. The trajectory of the dipole is related to the maximum potential vorticity anomaly and size of the vortices. Three cases are considered depending on the curvature of the dipole trajectory: negative, close to zero, and positive. The ageostrophic flow strongly depends on

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3

Ménesguen, Claire, J. C. McWilliams, and M. J. Molemaker. "Ageostrophic instability in a rotating stratified interior jet." Journal of Fluid Mechanics 711 (September 28, 2012): 599–619. http://dx.doi.org/10.1017/jfm.2012.412.

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AbstractOceanic large- and meso-scale flows are nearly balanced in forces between Earth’s rotation and density stratification effects (i.e. geostrophic, hydrostatic balance associated with small Rossby and Froude numbers). In this regime advective cross-scale interactions mostly drive energy toward larger scales (i.e. inverse cascade). However, viscous energy dissipation occurs at small scales. So how does the energy reservoir at larger scales leak toward small-scale dissipation to arrive at climate equilibrium? Here we solve the linear instability problem of a balanced flow in a rotating and

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4

VIÚDEZ, ÁLVARO. "The origin of the stationary frontal wave packet spontaneously generated in rotating stratified vortex dipoles." Journal of Fluid Mechanics 593 (November 23, 2007): 359–83. http://dx.doi.org/10.1017/s0022112007008816.

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The origin of the stationary frontal wave packet spontaneously generated in rotating and stably stratified vortex dipoles is investigated through high-resolution three-dimensional numerical simulations of non-hydrostatic volume-preserving flow under the f-plane and Boussinesq approximations. The wave packet is rendered better at mid-depths using ageostrophic quantities like the vertical velocity or the vertical shear of the ageostrophic vertical vorticity. The analysis of the origin of vertical velocity anomalies in shallow layers using the generalized omega-equation reveals that these anomali

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5

Wang, Peng, James C. McWilliams, and Ziv Kizner. "Ageostrophic instability in rotating shallow water." Journal of Fluid Mechanics 712 (September 28, 2012): 327–53. http://dx.doi.org/10.1017/jfm.2012.422.

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AbstractLinear instabilities, both momentum-balanced and unbalanced, in several different $ \overline{u} (y)$ shear profiles are investigated in the rotating shallow water equations. The unbalanced instabilities are strongly ageostrophic and involve inertia–gravity wave motions, occurring only for finite Rossby ($\mathit{Ro}$) and Froude ($\mathit{Fr}$) numbers. They serve as a possible route for the breakdown of balance in a rotating shallow water system, which leads the energy to cascade towards small scales. Unlike previous work, this paper focuses on general shear flows with non-uniform po

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6

Egger, Joseph, and Thomas Spengler. "Nonuniqueness of Attribution in Piecewise Potential Vorticity Inversion." Journal of the Atmospheric Sciences 75, no. 3 (2018): 875–83. http://dx.doi.org/10.1175/jas-d-17-0039.1.

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Abstract Piecewise potential vorticity inversion (PPVI) seeks to determine the impact of observed potential vorticity (PV) anomalies on the surrounding flow. This widely used technique is based on dividing a flow domain D into subdomains D1 and D2 = D − D1. The influence of PV in D1 on the flow in D2 is assessed by removing all PV anomalies in D2 and then inverting the modified PV in D. The resulting flow with streamfunction ψ1 is attributed to the PV anomalies in D1. The relation of PV in D1 to ψ1 in D2 is not unique, because there are many PV distributions in D1 that induce the same ψ1. Ther

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7

Thomas, Leif N. "On the effects of frontogenetic strain on symmetric instability and inertia–gravity waves." Journal of Fluid Mechanics 711 (September 20, 2012): 620–40. http://dx.doi.org/10.1017/jfm.2012.416.

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AbstractThe dynamics of symmetric instability and two-dimensional inertia–gravity waves in a baroclinic geostrophic flow undergoing frontogenesis is analysed. A frontogenetic strain associated with a balanced deformation field drives an ageostrophic circulation and temporal variations in the basic state that significantly affect the properties of perturbations to the background flow. For stable stratification, perturbations to the basic state result in symmetric instability or inertia–gravity waves, depending on the sign of the Ertel potential vorticity and the magnitude of the Richardson numb

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8

Kafiabad, Hossein A., and Peter Bartello. "Balance dynamics in rotating stratified turbulence." Journal of Fluid Mechanics 795 (April 22, 2016): 914–49. http://dx.doi.org/10.1017/jfm.2016.164.

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If classical quasigeostrophic (QG) flow breaks down at smaller scales, it gives rise to questions of whether higher-order nonlinear balance can be maintained, to what scale and for how long. These are naturally followed by asking how this is affected by stratification and rotation. To address these questions, we perform non-hydrostatic Boussinesq simulations where the initial data is balanced using the Baer–Tribbia nonlinear normal mode initialization scheme (NNMI), which is accurate to second order in the Rossby number, as the next-order improvement to first-order QG theory. The NNMI procedur

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9

Cai, Ming, and Bohua Huang. "A Dissection of Energetics of the Geostrophic Flow: Reconciliation of Rossby Wave Energy Flux and Group Velocity." Journal of the Atmospheric Sciences 70, no. 7 (2013): 2179–96. http://dx.doi.org/10.1175/jas-d-12-0249.1.

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Abstract It is shown in this paper that there is no ambiguity in the final form of the governing equations of a quasigeostrophic (QG) model after partitioning the total flow into the geostrophic, balanced ageostrophic, and unbalanced ageostrophic components. The uniqueness of the QG model formulation ensures that the energetics of a QG model is the same as that derived from the QG potential vorticity equation. Particularly, the well-known but somewhat mysterious “missing term” in the energetics of Rossby waves, identified in the literature as the difference between the pressure work and the en

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10

McWilliams, James C., and M. Jeroen Molemaker. "Baroclinic Frontal Arrest: A Sequel to Unstable Frontogenesis." Journal of Physical Oceanography 41, no. 3 (2011): 601–19. http://dx.doi.org/10.1175/2010jpo4493.1.

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Abstract In a large-scale deformation flow, lateral and vertical buoyancy gradients sharpen through baroclinic frontogenesis near the surface boundary. A “thermally direct” ageostrophic secondary circulation cell arises during frontogenesis to maintain geostrophic, hydrostatic (thermal wind) momentum balance for the alongfront flow. Unstable three-dimensional fluctuations can grow during frontogenesis by baroclinic instability of the alongfront shear flow that converts frontal potential energy to fluctuation energy. At finite amplitude, the fluctuations provide alongfront-averaged eddy momentu

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11

Ngan, K., P. Bartello, and D. N. Straub. "Dissipation of Synoptic-Scale Flow by Small-Scale Turbulence." Journal of the Atmospheric Sciences 65, no. 3 (2008): 766–91. http://dx.doi.org/10.1175/2007jas2265.1.

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Abstract Although it is now accepted that imbalance in the atmosphere and ocean is generic, the feedback of the unbalanced motion on the balanced flow has not received much attention. In this work the parameterization problem is examined in the context of rotating stratified turbulence, that is, with a nonhydrostatic Boussinesq model. Using the normal modes as a first approximation to the balanced and unbalanced flow, the growth of ageostrophic perturbations to the quasigeostrophic flow and the associated feedback are studied. For weak stratification, there are analogies with the three-dimensi

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12

Cronin, Meghan F., and William S. Kessler. "Near-Surface Shear Flow in the Tropical Pacific Cold Tongue Front*." Journal of Physical Oceanography 39, no. 5 (2009): 1200–1215. http://dx.doi.org/10.1175/2008jpo4064.1.

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Abstract Near-surface shear in the Pacific cold tongue front at 2°N, 140°W was measured using a set of five moored current meters between 5 and 25 m for nine months during 2004–05. Mean near-surface currents were strongly westward and only weakly northward (∼3 cm s−1). Mean near-surface shear was primarily westward and, thus, oriented to the left of the southeasterly trades. When the southwestward geostrophic shear was subtracted from the observed shear, the residual ageostrophic currents relative to 25 m were northward and had an Ekman-like spiral, in qualitative agreement with an Ekman model

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13

GULA, J., R. PLOUGONVEN, and V. ZEITLIN. "Ageostrophic instabilities of fronts in a channel in a stratified rotating fluid." Journal of Fluid Mechanics 627 (May 25, 2009): 485–507. http://dx.doi.org/10.1017/s0022112009006508.

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It is known that for finite Rossby numbers geostrophically balanced flows develop specific ageostrophic instabilities. We undertake a detailed study of the Rossby–Kelvin (RK) instability, previously studied by Sakai (J. Fluid Mech., vol. 202, 1989, pp. 149–176) in a two-layer rotating shallow-water model. First, we benchmark our method by reproducing the linear stability results obtained by Sakai (1989) and extend them to more general configurations. Second, in order to determine the relevance of RK instability in more realistic flows, simulations of the evolution of a front in a continuously

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14

SUTYRIN, GEORGI G. "Ageostrophic instabilities in a horizontally uniform baroclinic flow along a slope." Journal of Fluid Mechanics 588 (September 24, 2007): 463–73. http://dx.doi.org/10.1017/s0022112007006829.

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The normal modes of a horizontally uniform, vertically sheared flow over a sloping bottom are considered in two active layers underneath a deep motionless third layer. The variations of the layer thickness are assumed to be small to analyse the sixth-order eigenvalue problem for finite-Froude-number typical for oceanic currents. The dispersion curves for the Rossby waves and the Poincaré modes of inertia–gravity waves (IGW) are investigated to identify the different types of instabilities that occur if there is a pair of wave components which have almost the same Doppler-shifted frequency rela

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15

De Gregorio, S., and G. A. Dalu. "Ageostrophic (two-dimensional) flow of a rotating stratified fluid orographically perturbed." Il Nuovo Cimento C 10, no. 6 (1987): 609–30. http://dx.doi.org/10.1007/bf02507903.

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16

Sakai, Satoshi. "Rossby-Kelvin instability: a new type of ageostrophic instability caused by a resonance between Rossby waves and gravity waves." Journal of Fluid Mechanics 202 (May 1989): 149–76. http://dx.doi.org/10.1017/s0022112089001138.

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An ageostrophic version of Phillips’ model is studied. All instabilities found are systematically interpreted in terms of resonance of wave components. The instability occurs if there is a pair of wave components which propagate in the opposite direction to the basic flow and these wave components have almost the same Doppler-shifted frequency. A new instability, identified as a resonance between the Kelvin wave and the Rossby waves, is found at Froude number F ≈ 0.7. The Rossby waves are almost completely in geostrophic balance while the ageostrophic Kelvin wave is the same as in a one-layer

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17

McWilliams, James C. "Submesoscale surface fronts and filaments: secondary circulation, buoyancy flux, and frontogenesis." Journal of Fluid Mechanics 823 (June 20, 2017): 391–432. http://dx.doi.org/10.1017/jfm.2017.294.

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Problems are posed and solved for upper-ocean submesoscale density fronts and filaments in the presence of surface wind stress and the associated boundary-layer turbulent mixing, their associated geostrophic and secondary circulations and their instantaneous buoyancy fluxes and frontogenetic evolutionary tendencies in both velocity and buoyancy gradients. The analysis is diagnostic rather than prognostic, and it is based on a momentum-balanced approximation that assumes the ageostrophic acceleration is negligible, although the Rossby number is finite and ageostrophic advection is included, jus

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18

Wang, Peng, James C. McWilliams, and Claire Ménesguen. "Ageostrophic instability in rotating, stratified interior vertical shear flows." Journal of Fluid Mechanics 755 (August 19, 2014): 397–428. http://dx.doi.org/10.1017/jfm.2014.426.

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AbstractThe linear instability of several rotating, stably stratified, interior vertical shear flows $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\overline{U}(z)$ is calculated in Boussinesq equations. Two types of baroclinic, ageostrophic instability, AI1 and AI2, are found in odd-symmetric $\overline{U}(z)$ for intermediate Rossby number ($\mathit{Ro}$). AI1 has zero frequency; it appears in a continuous transformation of the

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19

Marcotte, Florence, Emmanuel Dormy, and Andrew Soward. "On the equatorial Ekman layer." Journal of Fluid Mechanics 803 (August 30, 2016): 395–435. http://dx.doi.org/10.1017/jfm.2016.493.

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The steady incompressible viscous flow in the wide gap between spheres rotating rapidly about a common axis at slightly different rates (small Rossby number) has a long and celebrated history. The problem is relevant to the dynamics of geophysical and planetary core flows, for which, in the case of electrically conducting fluids, the possible operation of a dynamo is of considerable interest. A comprehensive asymptotic study, in the small Ekman number limit $E\ll 1$, was undertaken by Stewartson (J. Fluid Mech., vol. 26, 1966, pp. 131–144). The mainstream flow, exterior to the $E^{1/2}$ Ekman

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20

Aoki, Kunihiro, Atsushi Kubokawa, Ryo Furue, and Hideharu Sasaki. "Influence of Eddy Momentum Fluxes on the Mean Flow of the Kuroshio Extension in a 1/10° Ocean General Circulation Model." Journal of Physical Oceanography 46, no. 9 (2016): 2769–84. http://dx.doi.org/10.1175/jpo-d-16-0021.1.

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AbstractThis study explores the role of the momentum flux divergence due to mesoscale eddies for the maintenance of the Kuroshio Extension (KE) jet. For that purpose, the zonal momentum budget in a high-resolution ocean general circulation model is examined on the basis of the temporal residual mean framework. The momentum budget analysis is performed for two control volumes: the upstream region of the KE jet flanked by the robust recirculations (33°–38°N and 142.2°–149.4°E) and the downstream region to the east (33°–38°N and 149.4°–160.0°E), both fully covering the meridional width of the KE

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21

Tanimoto, Youichi, Tomohisa Kanenari, Hiroki Tokinaga, and Shang-Ping Xie. "Sea Level Pressure Minimum along the Kuroshio and Its Extension*." Journal of Climate 24, no. 16 (2011): 4419–34. http://dx.doi.org/10.1175/2011jcli4062.1.

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Abstract Atmospheric effects of sea surface temperature (SST) fronts along the Kuroshio and Kuroshio Extension (K-KE) are investigated by examining spatial characteristics of the climatological sea level pressure (SLP), surface winds and surface heat flux (Q) fields based on an in situ observation dataset. A hydrostatic effect of the SST front is observed during the northwesterly monsoon characterized by a westward-extending low-SLP wedge (trough) slightly south of the peak in Q along the K-KE. Ageostrophic surface westerlies crossing SLP isobars toward a trough center are found north of the l

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22

SUTYRIN, GEORGI G. "Lack of balance in continuously stratified rotating flows." Journal of Fluid Mechanics 615 (November 25, 2008): 93–100. http://dx.doi.org/10.1017/s0022112008004059.

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Periodic linear waves in a vertically sheared flow are considered in a continuously stratified layer of rotating fluid between homogeneous layers along a sloping bottom. This generalized Phillips' configuration has cyclonic horizontal shear and supports the Rossby modes related to the thickness variations of the homogeneous layers and inertia–gravity waves (IGW). While long Rossby modes with streamwise wavenumber κ < f/V (f is the Coriolis parameter, V is the maximum velocity) can be approximated by a neutral balanced solution, short waves with κ > f/V are found to have an inertial criti

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23

Beron-Vera, F. J., A. Hadjighasem, Q. Xia, M. J. Olascoaga, and G. Haller. "Coherent Lagrangian swirls among submesoscale motions." Proceedings of the National Academy of Sciences 116, no. 37 (2018): 18251–56. http://dx.doi.org/10.1073/pnas.1701392115.

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The emergence of coherent Lagrangian swirls (CLSs) among submesoscale motions in the ocean is illustrated. This is done by applying recent nonlinear dynamics tools for Lagrangian coherence detection on a surface flow realization produced by a data-assimilative submesoscale-permitting ocean general circulation model simulation of the Gulf of Mexico. Both mesoscale and submesoscale CLSs are extracted. These extractions prove the relevance of coherent Lagrangian eddies detected in satellite-altimetry–based geostrophic flow data for the arguably more realistic ageostrophic multiscale flow.

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24

Chavanne, Cédric, Pierre Flament, and Klaus-Werner Gurgel. "Interactions between a Submesoscale Anticyclonic Vortex and a Front*." Journal of Physical Oceanography 40, no. 8 (2010): 1802–18. http://dx.doi.org/10.1175/2010jpo4055.1.

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Abstract The evolution of a submesoscale anticyclonic vortex was observed by high-frequency Doppler radio current meters and satellite radiometers. The vortex formed between two large cyclones to the southwest of Oahu, Hawaii. The radius of the core was ∼15 km; the azimuthal velocity reached 35 cm s−1; and the surface vorticity remained below −f for 9 days, reaching an extremum of −1.7f. The flow was ageostrophic near the center and around the periphery of the vortex. The initial growth may have been driven by negative wind stress curl in the lee of Oahu. The vortex was prone to inertial, symm

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25

McWilliams, James C., Jonathan Gula, and M. Jeroen Molemaker. "The Gulf Stream North Wall: Ageostrophic Circulation and Frontogenesis." Journal of Physical Oceanography 49, no. 4 (2019): 893–916. http://dx.doi.org/10.1175/jpo-d-18-0203.1.

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AbstractEastward zonal jets are common in the ocean and atmosphere, for example, the Gulf Stream and jet stream. They are characterized by atypically strong horizontal velocity, baroclinic vertical structure with an upward flow intensification, large change in the density stratification meridionally across the jet, large-scale meanders around a central latitude, narrow troughs and broad crests, and a sharp and vertically sloping northern (poleward) “wall” defined by horizontal maxima in the lateral gradients of both velocity and density. Measurements and realistic oceanic simulations show thes

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26

Boss, E., N. Paldor, and L. Thompson. "Stability of a potential vorticity front: from quasi-geostrophy to shallow water." Journal of Fluid Mechanics 315 (May 25, 1996): 65–84. http://dx.doi.org/10.1017/s0022112096002339.

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The linear stability of a simple two-layer shear flow with an upper-layer potential vorticity front overlying a quiescent lower layer is investigated as a function of Rossby number and layer depths. This flow configuration is a generalization of previously studied flows whose results we reinterpret by considering the possible resonant interaction between waves. We find that instabilities previously referred to as ‘ageostrophic’ are a direct extension of quasi-geostrophic instabilities.Two types of instability are discussed: the classic long-wave quasi-geostrophic baroclinic instability arising

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27

Chouksey, Manita, Carsten Eden, and Nils Brüggemann. "Internal Gravity Wave Emission in Different Dynamical Regimes." Journal of Physical Oceanography 48, no. 8 (2018): 1709–30. http://dx.doi.org/10.1175/jpo-d-17-0158.1.

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AbstractWe aim to diagnose internal gravity waves emitted from balanced flow and investigate their role in the downscale transfer of energy. We use an idealized numerical model to simulate a range of baroclinically unstable flows to mimic dynamical regimes ranging from ageostrophic to quasigeostrophic flows. Wavelike signals present in the simulated flows, seen for instance in the vertical velocity, can be related to gravity wave activity identified by frequency and frequency–wavenumber spectra. To explicitly assign the energy contributions to the balanced and unbalanced (gravity) modes, we pe

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28

Dong, Li, and Stephen J. Colucci. "The Role of Nonquasigeostrophic Forcing in Southern Hemisphere Blocking Onsets." Monthly Weather Review 143, no. 4 (2015): 1455–71. http://dx.doi.org/10.1175/mwr-d-14-00356.1.

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Abstract A generalized frictionless, adiabatic geostrophic zonal wind tendency equation is derived to diagnose the nonquasigeostrophic forcings to blocking onset in the Southern Hemisphere through case study and composite analysis. In general, the quasigeostrophic model is capable of representing the key physical processes associated with blocking onset in the troposphere reasonably well in most blocking cases. The consideration of nonquasigeostrophic forcings moderately improves the quasigeostrophic representation in a majority of the blocking events selected for this study, but not all event

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29

Estrada-Allis, S. N., B. Barceló-Llull, E. Pallàs-Sanz, et al. "Vertical Velocity Dynamics and Mixing in an Anticyclone near the Canary Islands." Journal of Physical Oceanography 49, no. 2 (2019): 431–51. http://dx.doi.org/10.1175/jpo-d-17-0156.1.

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AbstractThe complex structure of the vertical velocity field inside an anticyclonic eddy located just south of the Canary Islands is analyzed through a high-resolution ocean model. Based on the flow divergence, vertical velocity is decomposed into various forcing components. The analysis reveals that advection and stretching of vorticity are the most important forcing contributions to the vertical velocity within the eddy. In the mixed layer, a small-scale multipolar vertical velocity pattern dominates. This is the result of vertical mixing effects that enhance the surface vertical velocity by

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Klein, Patrice, Bach Lien Hua, Guillaume Lapeyre, Xavier Capet, Sylvie Le Gentil, and Hideharu Sasaki. "Upper Ocean Turbulence from High-Resolution 3D Simulations." Journal of Physical Oceanography 38, no. 8 (2008): 1748–63. http://dx.doi.org/10.1175/2007jpo3773.1.

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Abstract The authors examine the turbulent properties of a baroclinically unstable oceanic flow using primitive equation (PE) simulations with high resolution (in both horizontal and vertical directions). Resulting dynamics in the surface layers involve large Rossby numbers and significant vortical asymmetries. Furthermore, the ageostrophic divergent motions associated with small-scale surface frontogenesis are shown to significantly alter the nonlinear transfers of kinetic energy and consequently the time evolution of the surface dynamics. Such impact of the ageostrophic motions explains the

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Lahaye, Noé, and Vladimir Zeitlin. "Centrifugal, barotropic and baroclinic instabilities of isolated ageostrophic anticyclones in the two-layer rotating shallow water model and their nonlinear saturation." Journal of Fluid Mechanics 762 (November 27, 2014): 5–34. http://dx.doi.org/10.1017/jfm.2014.631.

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AbstractInstabilities of isolated anticyclonic vortices in the two-layer rotating shallow water model are studied at Rossby numbers up to two, with the main goal to understand the interplay between the classical centrifugal instability and other ageostrophic instabilities. We find that different types of instabilities with low azimuthal wavenumbers exist, and may compete. In a wide range of parameters, an asymmetric version of the standard centrifugal instability has larger growth rate than the latter. The dependence of the instabilities on the parameters of the flow, i.e. Rossby and Burger nu

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Davies-Jones, Robert. "The Frontogenetical Forcing of Secondary Circulations. Part II: Properties of Q Vectors in Exact Linear Solutions." Journal of the Atmospheric Sciences 66, no. 2 (2009): 244–60. http://dx.doi.org/10.1175/2008jas2803.1.

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Abstract An exact solution of the primitive equations (PEs) and the corresponding exact solutions of the alternative balance (AB), geostrophic momentum (GM), and quasigeostrophic (QG) equations are presented. The PE solution illustrates how the temperature and horizontal vorticity fields evolve in a linear horizontal flow with constant deformation and vertical vorticity when the initial temperature field is also linear, as well as how ageostrophic circulations are produced. The other exact solutions show the errors produced by the various approximations and confirm that the AB solution is more

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33

Nagai, Takeyoshi, Amit Tandon, Nicolas Gruber, and James C. McWilliams. "Biological and physical impacts of ageostrophic frontal circulations driven by confluent flow and vertical mixing." Dynamics of Atmospheres and Oceans 45, no. 3-4 (2008): 229–51. http://dx.doi.org/10.1016/j.dynatmoce.2007.12.001.

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Benilov, E. S. "On the stability of large-amplitude geostrophic flows in a two-layer fluid: the case of ‘strong’ beta-effect." Journal of Fluid Mechanics 284 (February 10, 1995): 137–58. http://dx.doi.org/10.1017/s0022112095000292.

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This paper examines the stability of two-layer geostrophic flows with large displacement of the interface and strong β-effect. Attention is focused on flows with non-monotonic interface profiles which are not covered by the Rayleigh-style stability theorems proved by Benilov (1992a, b) and Benilov & Cushman-Roisin (1994). For such flows the coefficient of the highest derivative in the corresponding boundary-value problem vanishes at the point where the depth profile has an extremum. Although this singularity is similar to a critical level, it cannot be regularized by the simplistic introdu

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Hart, John E. "Sidewall Instability and Eddy Generation in a Rotating Fluid Subject to Periodic Forcing." Applied Mechanics Reviews 47, no. 6S (1994): S118—S122. http://dx.doi.org/10.1115/1.3124385.

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Laboratory experiments concerned with the generation of waves and vortices by sidewall instability in a rotating cylinder containing a homogeneous liquid are described. Motions are driven by modulating the basic rotation rate Ω of the cylinder sinusoidally in time at amplitude δ and frequency γ. In addition, a rotating lid, revolving differentially at rate ω provides a steady bias to the motion. The basic state consists of an axisymmetric flow composed of solid body rotation, sloshing periodically in time, with a Stokes-Stewartson boundary layer at the cylinder’s vertical wall. This oscillator

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Chakraborty, Rishiraj, Aaron Coutino, and Marek Stastna. "Particle clustering and subclustering as a proxy for mixing in geophysical flows." Nonlinear Processes in Geophysics 26, no. 3 (2019): 307–24. http://dx.doi.org/10.5194/npg-26-307-2019.

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Abstract. The Eulerian point of view is the traditional theoretical and numerical tool to describe fluid mechanics. Some modern computational fluid dynamics codes allow for the efficient simulation of particles, in turn facilitating a Lagrangian description of the flow. The existence and persistence of Lagrangian coherent structures in fluid flow has been a topic of considerable study. Here we focus on the ability of Lagrangian methods to characterize mixing in geophysical flows. We study the instability of a strongly non-linear double-jet flow, initially in geostrophic balance, which forms qu

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HUA, BACH LIEN, JAMES C. McWILLIAMS, and PATRICE KLEIN. "Lagrangian accelerations in geostrophic turbulence." Journal of Fluid Mechanics 366 (July 10, 1998): 87–108. http://dx.doi.org/10.1017/s0022112098001001.

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A distinctive property of Lagrangian accelerations in geostrophic turbulence is that they are governed by the large and intermediate scales of the flow, both in time and space, so that the inertial part of the dynamics plays a much larger role than in three-dimensional turbulence where viscous effects are stronger. For the case of geostrophic turbulence on a β-plane, three terms contribute to the Lagrangian accelerations: the ageostrophic pressure gradient which often is the largest term, a meridional acceleration due to the β-effect, and an acceleration due to horizontally divergent ageostrop

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Cessi, Paola, and Christopher L. Wolfe. "Eddy-Driven Buoyancy Gradients on Eastern Boundaries and Their Role in the Thermocline." Journal of Physical Oceanography 39, no. 7 (2009): 1595–614. http://dx.doi.org/10.1175/2009jpo4063.1.

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Abstract It is demonstrated that eddy fluxes of buoyancy at the eastern and western boundaries maintain alongshore buoyancy gradients along the coast. Eddy fluxes arise near the eastern and western boundaries because on both coasts buoyancy gradients normal to the boundary are strong. The eddy fluxes are accompanied by mean vertical flows that take place in narrow boundary layers next to the coast where the geostrophic constraint is broken. These ageostrophic cells have a velocity component normal to the coast that balances the geostrophic mean velocity. It is shown that the dynamics in these

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Yin-Mao Wang, Mark, George Tai-Jen Chen, Chung-Chieh Wang, and Ying-Hwa Kuo. "A Case Study of the Cutoff Process and Latent Heating Effect in an Upper-Level Cold-Core Low during the Mei-Yu Season in East Asia." Monthly Weather Review 140, no. 6 (2012): 1725–47. http://dx.doi.org/10.1175/mwr-d-11-00306.1.

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Abstract Using observational data and model sensitivity test, the present study diagnosed the evolution of an upper-level trough over 2–7 May 1998 during the mei-yu season in East Asia, with a focus on the role of latent heating downstream from the trough on the cutoff process and the formation of the cold-core low (CCL). Compared with conceptual models based on dry dynamics, the formation process of this cutoff low (COL) was inconsistent with the model of migratory jet streak–trough interaction, but the evolution of the upper-level trough (including its narrowing and rotation of axis) and the

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Egger, Joseph. "Baroclinic Instability in the Eady Model: Interpretations." Journal of the Atmospheric Sciences 66, no. 6 (2009): 1856–59. http://dx.doi.org/10.1175/2008jas3014.1.

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Abstract The mechanism of baroclinic instability in the Eady model is interpreted by explicitly calculating the ageostrophic circulations related to the model’s hyperbolic basic functions. It is advantageous to perform the analysis at the midlevel where the model’s “barotropic” mode provides the streamfunction and the “baroclinic” mode represents the temperature. These modes interact and instability occurs if the horizontal advection of background potential temperature by the barotropic mode dominates over the vertical one because of the same mode at the midlevel. A rather simple picture of th

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Mak, Mankin, Yi Lu, and Yi Deng. "Dynamics of Upper-Level Frontogenesis in Baroclinic Waves." Journal of the Atmospheric Sciences 73, no. 7 (2016): 2699–714. http://dx.doi.org/10.1175/jas-d-15-0250.1.

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Abstract This paper reports a diagnosis of the structure and dynamics of upper-level fronts (ULFs) simulated with a high-resolution Weather Research and Forecasting Model with diabatic heating versus one without diabatic heating. The ULFs of both simulations develop in about 6 days as integral parts of intensifying baroclinic waves. Each has a curvilinear structure along the southern edge of a relatively narrow long tongue of high potential vorticity in which stratospheric air is subducted to different tropospheric levels by synoptic-scale subsidence. It resembles a veil in the sky of varying

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Skyllingstad, Eric D., Jenessa Duncombe, and Roger M. Samelson. "Baroclinic Frontal Instabilities and Turbulent Mixing in the Surface Boundary Layer. Part II: Forced Simulations." Journal of Physical Oceanography 47, no. 10 (2017): 2429–54. http://dx.doi.org/10.1175/jpo-d-16-0179.1.

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AbstractGeneration of ocean surface boundary layer turbulence and coherent roll structures is examined in the context of wind-driven and geostrophic shear associated with horizontal density gradients using a large-eddy simulation model. Numerical experiments over a range of surface wind forcing and horizontal density gradient strengths, combined with linear stability analysis, indicate that the dominant instability mechanism supporting coherent roll development in these simulations is a mixed instability combining shear instability of the ageostrophic, wind-driven flow with symmetric instabili

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Sanz, Enric Pallàs, and Álvaro Viúdez. "Diagnosing Mesoscale Vertical Motion from Horizontal Velocity and Density Data." Journal of Physical Oceanography 35, no. 10 (2005): 1744–62. http://dx.doi.org/10.1175/jpo2784.1.

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Abstract The mesoscale vertical velocity is obtained by solving a generalized omega equation (ω equation) using density and horizontal velocity data from three consecutive quasi-synoptic high-resolution surveys in the Alboran Sea. The Atlantic Jet (AJ) and the northern part of the Western Alboran Gyre (WAG) were observed as a large density anticyclonic front extending down to 200–230 m. The horizontal velocity uh in the AJ reached maxima of 1.2 m s−1 for the three surveys, with extreme Rossby numbers of ζ/f ≈ −0.9 in the WAG and +0.9 in the AJ (where ζ is the vertical vorticity and f is the Co

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Panayotova, Iordanka N. "A New Surface Model for β-Plane Turbulence". Journal of the Atmospheric Sciences 64, № 7 (2007): 2717–25. http://dx.doi.org/10.1175/jas3970.1.

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Abstract This paper introduces a new numerical model for studying wave–turbulence interactions in a continuously stratified rotating flow, having a uniform potential vorticity and a rigid boundary. The meridional variation in the Coriolis parameter (β effect), a channel geometry, and the first-order nonlinear terms in a small Rossby number expansion are included into the surface quasigeostrophic dynamics. The model contains important dynamical characteristics of three-dimensional flows such as advection by ageostrophic winds, and stretching and tilting of relative vorticity. Nevertheless, it h

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Mak, Mankin, Yi Lu, and Yi Deng. "Two Issues Concerning Surface Frontogenesis." Journal of the Atmospheric Sciences 74, no. 9 (2017): 2967–87. http://dx.doi.org/10.1175/jas-d-16-0171.1.

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Abstract With the Weather Research and Forecasting (WRF) Model specifically configured to simulate the intensification and evolution of an extratropical baroclinic wave, this study first investigates why cold fronts are characteristically longer, narrower, and more intense than warm fronts in the extratropical atmosphere. It is found that the differential thermal advection by the geostrophic and ageostrophic wind components in the two frontal regions results in a greater thermal contrast across the cold front. The length of the cold front is essentially the length scale of the intensifying bar

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Du, Yu, Yi-Leng Chen, and Qinghong Zhang. "Numerical Simulations of the Boundary Layer Jet off the Southeastern Coast of China." Monthly Weather Review 143, no. 4 (2015): 1212–31. http://dx.doi.org/10.1175/mwr-d-14-00348.1.

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Abstract A strong coastal boundary layer jet (CBLJ) (~8 m s−1) off the southeastern coast of China (around 28°N, 122°E) is found from the July 2006–11 hourly model data simulated by the Advanced Research Weather Research and Forecasting Model (WRF-ARW) with a 9-km horizontal grid. The southerly CBLJ has a jet core at the 925-hPa level, located along the western periphery of the west Pacific subtropical high (WPSH). The CBLJ is mainly contributed by large-scale enhancement by diurnal forcing and orographic effects by the coastal terrain along the southeastern China coast and the terrain of Taiw

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McWilliams, James C., and Baylor Fox-Kemper. "Oceanic wave-balanced surface fronts and filaments." Journal of Fluid Mechanics 730 (August 1, 2013): 464–90. http://dx.doi.org/10.1017/jfm.2013.348.

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AbstractA geostrophic, hydrostatic, frontal or filamentary flow adjusts conservatively to accommodate a surface gravity wave field with wave-averaged, Stokes-drift vortex and Coriolis forces in an altered balanced state. In this altered state, the wave-balanced perturbations have an opposite cross-front symmetry to the original geostrophic state; e.g. the along-front flow perturbation is odd-symmetric about the frontal centre while the geostrophic flow is even-symmetric. The adjustment tends to make the flow scale closer to the deformation radius, and it induces a cross-front shape displacemen

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Jones, D. A., A. Mahalov, and B. Nicolaenko. "A Numerical Study of an Operator Splitting Method for Rotating Flows with Large Ageostrophic Initial Data." Theoretical and Computational Fluid Dynamics 13, no. 2 (1999): 143. http://dx.doi.org/10.1007/s001620050009.

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Jones, D. A., A. Mahalov, and B. Nicolaenko. "A Numerical Study of an Operator Splitting Method for Rotating Flows with Large Ageostrophic Initial Data." Theoretical and Computational Fluid Dynamics 13, no. 2 (1999): 143–59. http://dx.doi.org/10.1007/s001620050012.

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CENEDESE, C., and P. F. LINDEN. "Cyclone and anticyclone formation in a rotating stratified fluid over a sloping bottom." Journal of Fluid Mechanics 381 (February 25, 1999): 199–223. http://dx.doi.org/10.1017/s0022112098003644.

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We discuss laboratory experiments with a continuous source or sink of fluid in a two-layer rotating environment which produces anticyclonic and cyclonic vortices, respectively. Experiments were carried out with a sloping bottom in order to simulate the β-effect and they were conducted for different values for the source/sink flow rate Q and the Coriolis parameter f. The Rossby number Ro of these vortices was small but finite and the flow was expected to be quasi-geostrophic. The qualitative behaviour of the anticyclonic and cyclonic vortices was generally similar, but it depended on the flow r

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