Advances in Geophysical Fluid Dynamics
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Editors
Dr. Jean Reinaud
Dr. Jean Reinaud
E-Mail
Collection Editor
School of Mathematics and Statistics, University of St. Andrews, North Haugh, St. Andrews KY169SS, UK
Interests: geophysical fluid dynamics; vortex equilibria; vortex stability and interactions
Special Issues, Collections and Topics in MDPI journals
Topical Collection Information
Dear Colleagues,
Geophysical Fluid Dynamics (GFD) is a relatively young, but rapidly growing, branch of fluid mechanics that deals with a great variety of the complex multiscale flow patterns and material properties of planetary atmospheres and oceans. These flow patterns are typically controlled by planetary rotation, various boundary conditions, and ubiquitous fluid density gradients. They interact with each other and combine on a large scale to establish the climate. GFD employs mathematical analysis, computational modeling, as well as laboratory experiments to deal with the fundamental aspects, analyses and, ultimately, interpretations of the observed phenomena. To a large degree, the observed complexity of geophysical motions is due to the nonlinearity of fluid dynamics, which connects GFD research with the other branches of fluid mechanics. This Topical Collection, “Advances in Geophysical Fluid Dynamics”, welcomes new research contributions to the field.
Dr. Jean Reinaud
Prof. Dr. Pavel S. Berloff
Collection Editors
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Keywords
- nonlinear dynamics
- general circulation of atmospheres and oceans
- geophysical turbulence, vortices and waves
- parameterizations of small-scale processes
- material transport and mixing
- hydrodynamic instabilities
- buoyancy driven processes
- boundary layer processes
Published Papers (3 papers)
2024
Open AccessArticle
Influence of a Background Shear Flow on Cyclone–Anticyclone Asymmetry in Ageostrophic Balanced Flows
by
William Joseph McKiver
Viewed by 569
Abstract
In this paper, we study how cyclonic and anticyclonic vortices adapt their shape and orientation to a background shear flow in an effort to understand geophysical vortices. Here we use a balanced model that incorporates the effects of rotation and density stratification to
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In this paper, we study how cyclonic and anticyclonic vortices adapt their shape and orientation to a background shear flow in an effort to understand geophysical vortices. Here we use a balanced model that incorporates the effects of rotation and density stratification to model the case of an isolated vortex of uniform potential vorticity subjected to a background shear flow that mimics the effect of surrounding vortices. We find equilibrium states and analyze their linear stability to determine the vortex characteristics at the margin of stability. Differences are found between the cyclonic and anticyclonic equilibria depending on the background flow parameters. When there is only horizontal strain, the vertical aspect ratio of the vortex does not change, whereas increasing the imposed background strain rate causes a change in the horizontal cross section, with cyclones being more deformed than anticyclones for a given value of strain. Vertical shear not only causes changes in the vertical axis but also causes the vortex to tilt away from it upright position. Overall, anticyclonic equilibria tend to have a more circular horizontal cross section, a longer vertical axis, and a larger tilt angle with respect to cyclonic equilibria. The strongest asymmetry between the horizontal cross section of cyclonic and anticyclonic vortices occurs for low values of vertical shear, while the strongest asymmetry in the vertical axes and tilt angle occurs for large vertical shear. Finally, by expanding the vortex shape and orientation in terms of the strain rate, we derive simple formulas that provide insights into how the vortex equilibria depend on the background flow.
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Open AccessArticle
The Effect of Domain Length and Initialization Noise on Direct Numerical Simulation of Shear Stratified Turbulence
by
Vashkar Palma, Daniel MacDonald and Mehdi Raessi
Viewed by 646
Abstract
Direct numerical simulation (DNS) has been employed with success in a variety of oceanographic applications, particularly for investigating the internal dynamics of Kelvin–Helmholtz (
KH) billows. However, it is difficult to relate these results directly with observations of ocean turbulence due to
[...] Read more.
Direct numerical simulation (DNS) has been employed with success in a variety of oceanographic applications, particularly for investigating the internal dynamics of Kelvin–Helmholtz (
KH) billows. However, it is difficult to relate these results directly with observations of ocean turbulence due to the significant scale differences involved (ocean shear layers are typically on the order of tens to hundreds of meters in thickness, compared to DNS studies, with layers on the order of one to tens of centimeters). As efforts continue to inform our understanding of geophysical-scale turbulence by extrapolating DNS results, it is important to understand the impact of model setup and initial conditions on the resulting turbulent quantities. Given that geophysical-scale measurements, whether through microstructures or other techniques, can only provide estimates of averaged TKE quantities (e.g., TKE dissipation or buoyancy flux), it may be necessary to compare mean turbulent quantities derived from DNS (i.e., across one or more complete billow evolutions) with ocean measurements. In this study, we analyze the effect of domain length and initial velocity noise on resulting turbulent quantities. Domain length is important, as dimensions that are not integer multiples of the natural
KH billow wavelength may compress or stretch the billows and impact their energetics. The addition of random noise in the initial velocity field is often used to trigger turbulence and suppress secondary instabilities; however, the impact of noise on the resulting turbulent energetics is largely unknown. In this study, we conclude that domain lengths on the order of 1.5 times the natural wavelength or less can affect the resulting turbulent energetics by a factor of two or more. We also conclude that increasing the amplitude of random initial velocity noise decreases the resulting turbulent energetics, but that different realizations of the random noise field may have an even greater impact than amplitude. These results should be considered when designing a DNS experiment.
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Open AccessArticle
N-Symmetric Interaction of N Hetons, II: Analysis of the Case of Arbitrary N
by
Konstantin V. Koshel, Mikhail A. Sokolovskiy, David G. Dritschel and Jean N. Reinaud
Viewed by 1052
Abstract
This paper seeks and examines
N-symmetric vortical solutions of the two-layer geostrophic model for the special case when the vortices (or eddies) have vanishing summed strength (circulation anomaly). This study is an extension [Sokolovskiy et al.
Phys. Fluids 2020, 32, 09660], where
[...] Read more.
This paper seeks and examines
N-symmetric vortical solutions of the two-layer geostrophic model for the special case when the vortices (or eddies) have vanishing summed strength (circulation anomaly). This study is an extension [Sokolovskiy et al.
Phys. Fluids 2020, 32, 09660], where the general formulation for arbitrary
N was given, but the analysis was only carried out for
. Here, families of stationary solutions are obtained and their properties, including asymptotic ones, are investigated in detail. From the point of view of geophysical applications, the results may help interpret the propagation of thermal anomalies in the oceans.
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