Intensification of Loop Current Frontal Eddies and their Interactions with the Loop Current and Surrounding Flow

2021 ◽  
Author(s):  
◽  
Luna Hiron
Keyword(s):  
Pressure Gradient ◽  
Nonlinear Term ◽  
Deepwater Horizon ◽  
Loop Current ◽  
Local Circulation ◽  
Geostrophic Velocity ◽  
Momentum Budget ◽  
Gradient Forces ◽  
Horizontal Density Gradient ◽  
Cold Core

Loop Current Frontal Eddies (LCFEs) are cold-core vortices located in the vicinity of the Loop Current (LC) and are known to intensify and play an essential role in the LC shedding. The amplification of the LCFEs also affects the local circulation. During the 2010 Deepwater Horizon oil spill, part of the oil was entrained around and inside an intensified LCFE. The goal of this research is to characterize the LCFE intensification and understand its effects on the LC and surrounding flow. Firstly, the LC-LCFE interaction was investigated using altimetry and a mooring array. The intensification of the observed LCFEs shows similar characteristics over time, independent of their location: a steep increase in kinetic energy, a corresponding decrease in SSH, and an increase in size. LCFE intensification is dependent on the distance from the LC front. As the LCFE grows, the flow at the interface with the LC becomes stronger and deeper, and the horizontal density gradient between the features increases. Further intensification of the LC front and the LCFEs is suggested to be driven by the advection (nonlinear) term and the pressure-gradient (linear) term in the momentum budget. Secondly, the ageostrophy of the LC meanders during LCFE intensification is assessed using HYCOM velocity and geostrophic velocity from altimetry. The results indicate that during strong meandering, especially before and during LC shedding and in the presence of frontal eddies, the centrifugal force becomes as important as the Coriolis and the pressure-gradient forces, i.e., the LC meanders are in gradient-wind balance. Finally, the ability of LCFEs to transport particles without exchange with the exterior (i.e., material coherence) is investigated. The results show that the frontal eddies can remain coherent for up to 20 days at the surface and up to 25 days at deeper layers. Particles inside the frontal eddies were tracked backward in time and showed that the material coherence of the eddies builds up from Gulf water and can drive cross-shelf exchange of particles, water properties, and nutrients.

Force balance in rapidly rotating Rayleigh–Bénard convection

2021 ◽  
Vol 928 ◽  
Author(s):  
Andrés J. Aguirre Guzmán ◽  
Matteo Madonia ◽  
Jonathan S. Cheng ◽  
Rodolfo Ostilla-Mónico ◽  
Herman J.H. Clercx ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Large Scale ◽  
Force Balance ◽  
Bénard Convection ◽  
Benard Convection ◽  
Buoyancy Forces ◽  
Kinetic Boundary Layers ◽  
Gradient Forces ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

The force balance of rotating Rayleigh–Bénard convection regimes is investigated using direct numerical simulation on a laterally periodic domain, vertically bounded by no-slip walls. We provide a comprehensive view of the interplay between governing forces both in the bulk and near the walls. We observe, as in other prior studies, regimes of cells, convective Taylor columns, plumes, large-scale vortices (LSVs) and rotation-affected convection. Regimes of rapidly rotating convection are dominated by geostrophy, the balance between Coriolis and pressure-gradient forces. The higher-order interplay between inertial, viscous and buoyancy forces defines a subdominant balance that distinguishes the geostrophic states. It consists of viscous and buoyancy forces for cells and columns, inertial, viscous and buoyancy forces for plumes, and inertial forces for LSVs. In rotation-affected convection, inertial and pressure-gradient forces constitute the dominant balance; Coriolis, viscous and buoyancy forces form the subdominant balance. Near the walls, in geostrophic regimes, force magnitudes are larger than in the bulk; buoyancy contributes little to the subdominant balance of cells, columns and plumes. Increased force magnitudes denote increased ageostrophy near the walls. Nonetheless, the flow is geostrophic as the bulk. Inertia becomes increasingly more important compared with the bulk, and enters the subdominant balance of columns. As the bulk, the near-wall flow loses rotational constraint in rotation-affected convection. Consequently, kinetic boundary layers deviate from the expected behaviour from linear Ekman boundary layer theory. Our findings elucidate the dynamical balances of rotating thermal convection under realistic top/bottom boundary conditions, relevant to laboratory settings and large-scale natural flows.

scholarly journals Buoyancy of Convective Vertical Motions in the Inner Core of Intense Hurricanes. Part I: General Statistics

2005 ◽  
Vol 133 (1) ◽  
pp. 188-208 ◽  
Author(s):  
Matthew D. Eastin ◽  
William M. Gray ◽  
Peter G. Black
Keyword(s):  
Pressure Gradient ◽  
Vertical Velocity ◽  
Potential Temperature ◽  
Vertical Acceleration ◽  
Water Loading ◽  
Mesoscale Structure ◽  
Convective Scale ◽  
The Mean ◽  
Gradient Forces ◽  
Perturbation Pressure

Abstract The buoyancy of hurricane convective vertical motions is studied using aircraft data from 175 radial legs collected in 14 intense hurricanes at four altitudes ranging from 1.5 to 5.5 km. The data of each leg are initially filtered to separate convective-scale features from background mesoscale structure. Convective vertical motion events, called cores, are identified using the criteria that the convective-scale vertical velocity must exceed 1.0 m s−1 for at least 0.5 km. A total of 620 updraft cores and 570 downdraft cores are included in the dataset. Total buoyancy is calculated from convective-scale virtual potential temperature, pressure, and liquid water content using the mesoscale structure as the reference state. Core properties are summarized for the eyewall and rainband regions at each altitude. Characteristics of core average convective vertical velocity, maximum convective vertical velocity, and diameter are consistent with previous studies of hurricane convection. Most cores are superimposed upon relatively weak mesoscale ascent. The mean eyewall (rainband) updraft core exhibits small, but statistically significant, positive total buoyancy below 4 km (between 2 and 5 km) and a modest increase in vertical velocity with altitude. The mean downdraft core not superimposed upon stronger mesoscale ascent also exhibits positive total buoyancy and a slight decrease in downward vertical velocity with decreasing altitude. Buoyant updraft cores cover less than 5% of the total area in each region but accomplish ∼40% of the total upward transport. A one-dimensional updraft model is used to elucidate the relative roles played by buoyancy, vertical perturbation pressure gradient forces, water loading, and entrainment in the vertical acceleration of ordinary updraft cores. Small positive total buoyancy values are found to be more than adequate to explain the vertical accelerations observed in updraft core strength, which implies that ordinary vertical perturbation pressure gradient forces are directed downward, opposing the positive buoyancy forces. Entrainment and water loading are also found to limit updraft magnitudes. The observations support some aspects of both the hot tower hypothesis and symmetric moist neutral ascent, but neither concept appears dominant. Buoyant convective updrafts, however, are integral components of the hurricane’s transverse circulation.

scholarly journals Lateral Circulation in Well-Mixed and Stratified Estuarine Flows with Curvature

2009 ◽  
Vol 39 (4) ◽  
pp. 831-851 ◽  
Author(s):  
Nicholas J. Nidzieko ◽  
James L. Hench ◽  
Stephen G. Monismith
Keyword(s):  
Pressure Gradient ◽  
Tidal Flow ◽  
Centrifugal Acceleration ◽  
Residual Currents ◽  
Momentum Budget ◽  
Current Profiler ◽  
Lateral Circulation ◽  
Layer Flow ◽  
Forcing Mechanisms ◽  
Temperature Depth

Abstract A field experiment was conducted to examine stratified and unstratified curvature-generated lateral circulation and momentum balances in an estuarine tidal channel. Conductivity, temperature, depth, and current profiler data were collected vertically and laterally across the channel at a sharp bend over a fortnightly period to measure the terms of the lateral momentum budget. Well-mixed conditions allow the development of classic two-layer helical flow around a bend. Stratification strengthens curvature-induced lateral circulation, but the development of a lateral baroclinic pressure gradient opposes the resultant motions. The spatial and temporal response of this baroclinic pressure gradient is different than centrifugal acceleration, producing a three-layer profile. As the baroclinic term becomes stronger (or as centrifugal acceleration disappears as the flow exits the bend), two-layer flow with the opposite direction from curvature occurs. In both stratified and well-mixed conditions, downstream adjustment of lateral circulation (nonlinear advective acceleration) is of leading order in the lateral momentum budget; the depth-averaged term adjusts the streamline direction, while vertical deviations from the depth average account for changes in lateral circulation. The asymmetry of forcing mechanisms on flood and ebb, because of variations in stratification and strength of tidal flow, can strongly affect net lateral transport and generation of residual currents in regions of curvature.

Study of ageostrophy during strong, nonlinear eddy-front interaction in the Gulf of Mexico

2020 ◽  
Author(s):  
Luna Hiron ◽  
David S. Nolan ◽  
Lynn K. Shay
Keyword(s):  
Centrifugal Force ◽  
Nonlinear Term ◽  
Flow Speed ◽  
Radius Of Curvature ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Loop Current ◽  
Geostrophic Balance ◽  
Gradient Wind ◽  
Geostrophic Velocities

AbstractThe Loop Current (LC) system has long been assumed to be close to geostrophic balance despite its strong flow and the development of large meanders and strong frontal eddies during unstable phases. The region between the LC meanders and its frontal eddies was shown to have high Rossby numbers indicating nonlinearity; however, the effect of the nonlinear term on the flow has not been studied so far. In this study, the ageostrophy of the LC meanders is assessed using a high-resolution numerical model and geostrophic velocities from altimetry. A formula to compute the radius of curvature of the flow from the velocity field is also presented. The results indicate that during strong meandering, especially before and during LC shedding and in the presence of frontal eddies, the centrifugal force becomes as important as the Coriolis force and the pressure-gradient force: LC meanders are in gradient-wind balance. The centrifugal force modulates the balance and modifies the flow speed, resulting in a subgeostrophic flow in the LC meander trough around the LCFE and supergeostrophic flow in the LC meander crest. The same pattern is found when correcting the geostrophic velocities from altimetry to account for the centrifugal force. The ageostrophic percentage in the cyclonic and anticyclonic meanders is 47% ± 1% and 78% ± 8% in the model and 31% ± 3% and 78% ± 29% in the altimetry dataset, respectively. Thus, the ageostrophic velocity is an important component of the LC flow and cannot be neglected when studying the LC system.

Mesoscale meteorological conditions in Dronning Maud Land, Antarctica, during summer: the momentum budget of the boundary layer

2000 ◽  
Vol 12 (2) ◽  
pp. 229-242 ◽  
Author(s):  
Richard Bintanja
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Time Of Day ◽  
Meteorological Conditions ◽  
Forced Flow ◽  
Research Station ◽  
General Description ◽  
Momentum Budget ◽  
Synoptic Conditions ◽  
Dronning Maud Land

The momentum budget of the boundary layer flew near the Swedish research station Svea in the mountainous region of western Dronning Maud Land, Antarctica, is evaluated using detailed concurrent observations of surface meteorological variables, high-resolution boundary layer profiles and upper-air profiles taken during the summer of 1997–98. Despite the fact that the irregular topographical situation prohibits easy interpretation of the data, interesting features can still be identified. All terms in the momentum budget (katabatic forcing, synoptic pressure gradient, Coriolis force and friction) can be of the same order of magnitude, which indicates that the influence of each term depends largely on the prevailing conditions. More precisely, the relative importance of the various momentum terms varies strongly with altitude, location, time of day and prevailing synoptic conditions. For example, at the undisturbed snow slopes there is a very regular daily variation of katabatically forced flow during the night and a flow dominated by the synoptic pressure gradient during the day, causing a persistent diurnal cycle in surface wind direction. The interpretation of the flow characteristics in terms of the momentum budget agrees favourably with the conclusions drawn on the basis of a general description of the prevailing meteorological conditions, and can therefore be considered consistent.

Dynamics of revolving wings for various aspect ratios

2014 ◽  
Vol 748 ◽  
pp. 932-956 ◽  
Author(s):  
D. J. Garmann ◽  
M. R. Visbal
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Pressure Gradient ◽  
Centrifugal Force ◽  
Vortex Breakdown ◽  
Delta Wing ◽  
Strong Dependence ◽  
Tip Vortex ◽  
Aspect Ratios ◽  
Gradient Forces

AbstractHigh-fidelity, direct numerical simulations (DNSs) are conducted to examine the vortex structure and aerodynamic loading of unidirectionally revolving wings in quiescent fluid. Wings with aspect ratios $({\mathit{AR}}) = 1$, 2 and 4 are considered at a fixed root-based Reynolds number of 1000. Each wing is shown to generate a coherent leading-edge vortex (LEV) that remains in close proximity to the surface and provides persistent suction throughout the motion. Towards the tip, the LEV lifts off as an arch-like structure and reorients itself along the chord through its connection with the tip vortex. The substantial and sustained aerodynamic loads achieved during the motion saturate with aspect ratio resulting from the chordwise growth of the LEV along the span eventually becoming geometrically constrained by the trailing edge. Further, for ${\mathit{AR}}=4$, substructures develop in the feeding sheet of the LEV, which appear to directly correlate with the local, span-based Reynolds number achieved during rotation. The lower-aspect-ratio wings do not have sufficient spans for these transitional elements to manifest. In contrast, vortex breakdown, which occurs around midspan for each aspect ratio, shows a strong dependence on the spanwise pressure gradient established between the root and tip of the wing and not local Reynolds number. This independent development of shear-layer substructures and vortex breakdown parallels very closely with what has been observed in delta wing flow. Next, the centrifugal, Coriolis and pressure gradient forces are also analysed at several spanwise locations across each wing, and the centrifugal and pressure gradient forces are shown to be responsible for the spanwise flow above the wing. The Coriolis force is directed away from the surface at the base of the LEV, indicating that it is not a contributor to LEV attachment, which is contrary to previous hypotheses. Finally, as a means of emphasizing the importance of the centrifugal force on LEV attachment, the ${\mathit{AR}}=2$ wing is simulated with the addition of a source term in the governing equations to oppose and eliminate the centrifugal force near the surface. The initial formation and development of the LEV is unhindered by the absence of this force; however, later in the motion, the outboard lift-off of the LEV moves inboard. Without the opposing outboard-directed centrifugal force to keep the separation past midspan, the entire vortex eventually separates and moves away from the surface.

scholarly journals The Role of Mesoscale Dynamics over Northwestern Cuba in the Loop Current Evolution in 2010, during the Deepwater Horizon Incident

2021 ◽  
Vol 9 (2) ◽  
pp. 188
Author(s):  
Yannis Androulidakis ◽  
Vassiliki Kourafalou ◽  
Matthieu Le Hénaff ◽  
HeeSook Kang ◽  
Nektaria Ntaganou
Keyword(s):  
Oil Spill ◽  
Deepwater Horizon ◽  
Main Body ◽  
Florida Current ◽  
Loop Current ◽  
Straits Of Florida ◽  
Eddy Activity ◽  
Mesoscale Dynamics ◽  
Resolution Model ◽  
Yucatan Channel

The Loop Current (LC) system controls the connectivity between the northern Gulf of Mexico (GoM) region and the Straits of Florida. The evolution of the LC and the shedding sequence of the LC anticyclonic ring (Eddy Franklin) were crucial for the fate of the hydrocarbons released during the Deepwater Horizon (DwH) oil spill in 2010. In a previous study, we identified LC-related anticyclonic eddies in the southern GoM, named “Cuba anticyclones” (“CubANs”). Here, we investigate the relation between these eddies and LC evolution in 2010, focusing on the DwH period. We use high-resolution model results in tandem with observational data to describe the connection between the LC system evolution within the GoM (LC extensions, Eddy Franklin and LC Frontal Eddies—LCFEs) and the mesoscale dynamics within the Straits of Florida where CubANs propagate. Five periods of CubAN eddy activity were identified during the oil spill period, featuring different formation processes under a combination of local and regional conditions. Most of these cases are related to the retracted LC phases, when the major LC anticyclone (Eddy Franklin in 2010) is detached from the main body and CubAN eddy activity is most likely. However, two cases of CubAN eddy presence during elongated LC were detected, which led to the attenuation of the eastward flows of warm waters through the Straits (Florida Current; outflow), allowing the stronger supply of Caribbean waters through the Yucatan Channel into the Gulf (inflow), which contributed to short-term LC northward extensions. Oceanographic (LCFEs) and meteorological (wind-induced upwelling) conditions contributed to the release of CubANs from the main LC body, which, in tandem with other processes, contributed to the LC evolution during the DwH oil spill incident.

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