Strong long-lived anticyclonic mesoscale eddies in the Balearic Sea: formation and intensification mechanisms

Anticyclonic mesoscale eddies are often formed in the Balearic Sea towards the end of summer and autumn. In some years, these eddies become strong and persistent, modifying the ocean currents and water mass properties in the area. The generation and intensification mechanisms of two long-lived events observed in 2010 and 2017 were studied by means of the energy conversion terms associated with eddy-mean flow interactions and through complementary model sensitivity tests.Results show that these eddies were formed through mixed barotropic and baroclinic instabilities. The former was associated with weak meandering of the shelf current near the coast produced by northwesterly wind events, and the latter with the existence of the northward intrusions of relatively warm waters through the intense Pyrenees thermal front. The intensification mechanism varied between the two events. While in 2010 it was driven by intense salinity gradients in the Balearic Sea, in 2017 it resulted from an extra barotropic energy term fed by northwesterly winds.These eddies lasted more than two months with a radius varying between 30km and 90km and a vertical structure that reached 1500 m depth. Their presence resulted in a 3&#186;C anomaly between the warm core waters and the outer parts of the eddies.

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Spatiotemporal Variability of Mesoscale Eddies in the Indonesian Seas

Remote Sensing ◽

10.3390/rs13051017 ◽

2021 ◽

Vol 13 (5) ◽

pp. 1017

Author(s):

Zhanjiu Hao ◽

Zhenhua Xu ◽

Ming Feng ◽

Qun Li ◽

Baoshu Yin

Keyword(s):

World Ocean ◽

Mesoscale Eddies ◽

Spatial Inhomogeneity ◽

Spatiotemporal Variability ◽

Identification Algorithm ◽

Mean Flow ◽

Sulu Sea ◽

Indonesian Seas ◽

Highly Nonlinear ◽

Eddy Generation

Mesoscale eddies are ubiquitous in the world ocean and well researched both globally and regionally, while their properties and distributions across the whole Indonesian Seas are not yet fully understood. This study investigates for the first time the spatiotemporal variations and generation mechanisms of mesoscale eddies across the whole Indonesian Seas. Eddies are detected from altimetry sea level anomalies by an automatic identification algorithm. The Sulu Sea, Sulawesi Sea, Maluku Sea and Banda Sea are the main eddy generation regions. More than 80% of eddies are short-lived with a lifetime below 30 days. The properties of eddies exhibit high spatial inhomogeneity, with the typical amplitudes and radiuses of 2–6 cm and 50–160 km, respectively. The most energetic eddies are observed in the Sulawesi Sea and Seram Sea. Eddies feature different seasonal cycles between anticyclonic and cyclonic eddies in each basin, especially given that the average latitude of the eddy centroid has inverse seasonal variations. About 48% of eddies in the Sulawesi Sea are highly nonlinear, which is the case for less than 30% in the Sulu Sea and Banda Sea. Instability analysis is performed using high-resolution model outputs from Bluelink Reanalysis to assess mechanisms of eddy generation. Barotropic instability of the mean flow dominates eddy generation in the Sulu Sea and Sulawesi Sea, while baroclinic instability is slightly more in the Maluku Sea and Banda Sea.

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Eddy-mean flow interactions and vertical eddy energy redistribution associated with the standing meander in the Antarctic Circumpolar Current

10.1002/essoar.10506510.1 ◽

2021 ◽

Author(s):

Takuro Matsuta ◽

Yukio Masumoto

Keyword(s):

Antarctic Circumpolar Current ◽

Mean Flow ◽

Energy Redistribution ◽

Flow Interactions ◽

Circumpolar Current ◽

The Antarctic ◽

Vertical Eddy

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Wave-mean flow interactions in the upper atmosphere

Boundary-Layer Meteorology ◽

10.1007/bf02265242 ◽

1973 ◽

Vol 4 (1-4) ◽

pp. 327-343 ◽

Cited By ~ 48

Author(s):

Richard S. Lindzen

Keyword(s):

Upper Atmosphere ◽

Mean Flow ◽

Flow Interactions

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Advancing the simulation of mesoscale eddies: Backscatter schemes in eddy-permitting ocean simulations

10.5194/egusphere-egu21-12418 ◽

2021 ◽

Author(s):

Stephan Juricke ◽

Sergey Danilov ◽

Marcel Oliver ◽

Nikolay Koldunov ◽

Dmitry Sidorenko ◽

...

Keyword(s):

Kinetic Energy ◽

Large Scale ◽

Mesoscale Eddy ◽

Ocean Model ◽

Mean Flow ◽

Ocean Coupling ◽

Climate Simulations ◽

Flow Interactions ◽

To Come ◽

Eddy Dynamics

Capturing mesoscale eddy dynamics is crucial for accurate simulations of the large-scale ocean currents as well as oceanic and climate variability. Eddy-mean flow interactions affect the position, strength and variations of mean currents and eddies are important drivers of oceanic heat transport and atmosphere-ocean-coupling. However, simulations at eddy-permitting resolutions are substantially underestimating eddy variability and eddy kinetic energy many times over. Such eddy-permitting simulations will be in use for years to come, both in coupled and uncoupled climate simulations. We present a set of kinetic energy backscatter schemes with different complexity as alternative momentum closures that can alleviate some eddy related biases such as biases in the mean currents, in sea surface height variability and in temperature and salinity. The complexity of the schemes reflects in their computational costs, the related simulation improvements and their adaptability to different resolutions. However, all schemes outperform classical viscous closures and are computationally less expensive than a related necessary resolution increase to achieve similar results. While the backscatter schemes are implemented in the ocean model FESOM2, the concepts can be adjusted to any ocean model including NEMO.

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Wave-Mean-Flow Interactions

The Stratosphere and Its Role in the Climate System ◽

10.1007/978-3-662-03327-2_5 ◽

1997 ◽

pp. 47-57

Author(s):

James R. Holton

Keyword(s):

Mean Flow ◽

Flow Interactions

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On the Role of Asymmetric Convective Bursts to the Problem of Hurricane Intensification: Radiation of Vortex Rossby Waves and Wave–Mean Flow Interactions

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-0343.1 ◽

2014 ◽

Vol 71 (6) ◽

pp. 2057-2077 ◽

Cited By ~ 9

Author(s):

Konstantinos Menelaou ◽

M. K. Yau

Keyword(s):

Kinetic Energy ◽

Thermal Anomaly ◽

Eddy Kinetic Energy ◽

Intensity Change ◽

Mean Flow ◽

Symmetric Flow ◽

Thermal Forcing ◽

Sensitivity Experiments ◽

Flow Interactions

Abstract The role of asymmetric convection to the intensity change of a weak vortex is investigated with the aid of a “dry” thermally forced model. Numerical experiments are conducted, starting with a weak vortex forced by a localized thermal anomaly. The concept of wave activity, the Eliassen–Palm flux, and eddy kinetic energy are then applied to identify the nature of the dominant generated waves and to diagnose their kinematics, structure, and impact on the primary vortex. The physical reasons for which disagreements with previous studies exist are also investigated utilizing the governing equation for potential vorticity (PV) perturbations and a number of sensitivity experiments. From the control experiment, it is found that the response of the vortex is dominated by the radiation of a damped sheared vortex Rossby wave (VRW) that acts to accelerate the symmetric flow through the transport of angular momentum. An increase of the kinetic energy of the symmetric flow by the VRW is shown also from the eddy kinetic energy budget. Additional tests performed on the structure and the magnitude of the initial thermal forcing confirm the robustness of the results and emphasize the significance of the wave–mean flow interaction to the intensification process. From the sensitivity experiments, it is found that for a localized thermal anomaly, regardless of the baroclinicity of the vortex and the radial and vertical gradients of the thermal forcing, the resultant PV perturbation follows a damping behavior, thus suggesting that deceleration of the vortex should not be expected.

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Observed Storm Track Dynamics in Drake Passage

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0150.1 ◽

2019 ◽

Vol 49 (3) ◽

pp. 867-884 ◽

Cited By ~ 1

Author(s):

Annie Foppert

Keyword(s):

Mean Field ◽

Storm Track ◽

Drake Passage ◽

Polar Front ◽

Mean Flow ◽

Track Dynamics ◽

Flow Interactions ◽

Circumpolar Current ◽

Eddy Potential Energy ◽

Shackleton Fracture Zone

AbstractThe dynamics of an oceanic storm track—where energy and enstrophy transfer between the mean flow and eddies—are investigated using observations from an eddy-rich region of the Antarctic Circumpolar Current downstream of the Shackleton Fracture Zone (SFZ) in Drake Passage. Four years of measurements by an array of current- and pressure-recording inverted echo sounders deployed between November 2007 and November 2011 are used to diagnose eddy–mean flow interactions and provide insight into physical mechanisms for these transfers. Averaged within the upper to mid-water column (400–1000-m depth) and over the 4-yr-record mean field, eddy potential energy is highest in the western part of the storm track and maximum eddy kinetic energy occurs farther away from the SFZ, shifting the proportion of eddy energies from to about 1 along the storm track. There are enhanced mean 3D wave activity fluxes immediately downstream of SFZ with strong horizontal flux vectors emanating northeast from this region. Similar patterns across composites of Polar Front and Subantarctic Front meander intrusions suggest the dynamics are set more so by the presence of the SFZ than by the eddy’s sign. A case study showing the evolution of a single eddy event, from 15 to 23 July 2010, highlights the storm-track dynamics in a series of snapshots. Consistently, explaining the eddy energetics pattern requires both horizontal and vertical components of W, implying the importance of barotropic and baroclinic processes and instabilities in controlling storm-track dynamics in Drake Passage.

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Nonlinear Saturation of Vertically Propagating Rossby Waves

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2978.1 ◽

2009 ◽

Vol 66 (4) ◽

pp. 915-934 ◽

Cited By ~ 2

Author(s):

Constantine Giannitsis ◽

Richard S. Lindzen

Keyword(s):

Wave Propagation ◽

Channel Model ◽

Plane Channel ◽

Nonlinear Flow ◽

Computational Domain ◽

Mean Flow ◽

Wave Interactions ◽

Linear Solution ◽

Wave Growth ◽

Flow Interactions

Abstract The interaction between vertical Rossby wave propagation and wave breaking is studied in the idealized context of a beta-plane channel model. Considering the problem of propagation through a uniform zonal flow in an exponentially stratified fluid, where linear theory predicts exponential wave growth with height, the question is how wave growth is limited in the nonlinear flow. Using a numerical model, the authors examine the behavior of the flow as the bottom forcing increases through values bound to lead to a breakdown of the linear solution within the computational domain. Focusing on the equilibrium flow obtained for each value of the bottom forcing, an attempt is made to identify the mechanisms involved in limiting wave growth and examine in particular the importance of wave–wave interactions. The authors also examine the case in which forcing is continuously increasing with time so as to enhance effects peculiar to transiency; it does not significantly alter the main results. Wave–mean flow interactions are found to dominate the dynamics even for strong bottom forcing values. Ultimately, it is the modification of the mean flow that is found to limit the vertical penetration of the forced wave, through either increased wave absorption or downward reflection. Linear propagation theory is found to capture the wave structure surprisingly well, even when the total flow is highly deformed. Overall, the numerical results seem to suggest that wave–wave interactions do not have a strong direct effect on the propagating disturbance. Wave–mean flow interactions limit wave growth sufficiently that a strong additional nonlinear enstrophy sink, through downscale cascade, is not necessary. Quantitatively, however, wave–wave interactions, primarily among the lowest wavenumbers, prove important so as to sufficiently accurately determine the basic state and its influence on wave propagation.

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