scholarly journals Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 185-205 ◽  
Author(s):  
C. Q. C. Akuetevi ◽  
B. Barnier ◽  
J. Verron ◽  
J.-M. Molines ◽  
A. Lecointre
Keyword(s):  
Ocean Circulation ◽  
Numerical Study ◽  
Current System ◽  
Subsequent Development ◽  
Southwest Monsoon ◽  
Global Ocean ◽  
Socotra Island ◽  
Eddy Structures ◽  
Somali Current ◽  
Global Ocean Circulation

Abstract. Three hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Donohue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations.

scholarly journals Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

2015 ◽  
Vol 12 (3) ◽  
pp. 735-767 ◽  
Author(s):  
C. Q. C. Akuetevi ◽  
B. Barnier ◽  
J. Verron ◽  
J.-M. Molines ◽  
A. Lecointre
Keyword(s):  
Ocean Circulation ◽  
Numerical Study ◽  
Current System ◽  
Subsequent Development ◽  
Southwest Monsoon ◽  
Global Ocean ◽  
Socotra Island ◽  
Eddy Structures ◽  
Somali Current ◽  
Global Ocean Circulation

Abstract. Three hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parameterization or atmospheric forcing are used to study the fast interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Donohue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as major actors in mixing water masses within the large eddies and offshore the coast of Somali. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounter the GW. The interaction between the SG and the GW is a collision without merging, collision during which the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for the Socotra Eddy. During this process, the GW gives up its place to the SG which in turn becomes a new Great Whirl. This process is robust throughout the three simulations.

scholarly journals Double-diffusive mixing makes a small contribution to the global ocean circulation

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Carine G. van der Boog ◽  
Henk A. Dijkstra ◽  
Julie D. Pietrzak ◽  
Caroline A. Katsman
Keyword(s):  
Ocean Circulation ◽  
Mechanical Energy ◽  
Global Ocean ◽  
Small Contribution ◽  
Global Ocean Circulation ◽  
Diffusive Fluxes ◽  
Diffusive Mixing ◽  
Diffusive Processes ◽  
Flowing Waters ◽  
Double Diffusive

AbstractDouble-diffusive processes enhance diapycnal mixing of heat and salt in the open ocean. However, observationally based evidence of the effects of double-diffusive mixing on the global ocean circulation is lacking. Here we analyze the occurrence of double-diffusive thermohaline staircases in a dataset containing over 480,000 temperature and salinity profiles from Argo floats and Ice-Tethered Profilers. We show that about 14% of all profiles contains thermohaline staircases that appear clustered in specific regions, with one hitherto unknown cluster overlying the westward flowing waters of the Tasman Leakage. We estimate the combined contribution of double-diffusive fluxes in all thermohaline staircases to the global ocean’s mechanical energy budget as 7.5 GW [0.1 GW; 32.8 GW]. This is small compared to the estimated energy required to maintain the observed ocean stratification of roughly 2 TW. Nevertheless, we suggest that the regional effects, for example near Australia, could be pronounced.

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

scholarly journals Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution

2006 ◽  
Vol 56 (5-6) ◽  
pp. 543-567 ◽  
Author(s):  
Barnier Bernard ◽  
Gurvan Madec ◽  
Thierry Penduff ◽  
Jean-Marc Molines ◽  
Anne-Marie Treguier ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Ocean Circulation Model ◽  
Advection Schemes ◽  
Global Ocean Circulation

scholarly journals Viscosity and elasticity: a model intercomparison of ice-shelf bending in an Antarctic grounding zone

2017 ◽  
Vol 63 (240) ◽  
pp. 573-580 ◽  
Author(s):  
CHRISTIAN T. WILD ◽  
OLIVER J. MARSH ◽  
WOLFGANG RACK
Keyword(s):  
Young’S Modulus ◽  
Ocean Circulation ◽  
Young's Modulus ◽  
Viscoelastic Model ◽  
Ice Sheet ◽  
Global Ocean ◽  
Elastic Model ◽  
Ice Shelf ◽  
Bending Stresses ◽  
Global Ocean Circulation

ABSTRACTGrounding zones are vital to ice-sheet mass balance and its coupling to the global ocean circulation. Processes here determine the mass discharge from the grounded ice sheet, to the floating ice shelves. The response of this transition zone to tidal forcing has been described by both elastic and viscoelastic models. Here we examine the validity of these models for grounding zone flexure over tidal timescales using field data from the Southern McMurdo Ice Shelf (78° 15′S, 167° 7′E). Observations of tidal movement were carried out by simultaneous tiltmeter and GPS measurements along a profile across the grounding zone. Finite-element simulations covering a 64 d period reveal that the viscoelastic model fits best the observations using a Young's modulus of 1.6 GPa and a viscosity of 1013.7 Pa s (≈ 50.1 TPa s). We conclude that the elastic model is only well-constrained for tidal displacements >35% of the spring-tidal amplitude using a Young's modulus of 1.62 ± 0.69 GPa, but that a viscoelastic model is necessary to adequately capture tidal bending at amplitudes below this threshold. In grounding zones where bending stresses are greater than at the Southern McMurdo Ice Shelf or ice viscosity is lower, the threshold would be even higher.

Electromagnetic fields generated by a three dimensional global ocean circulation

1997 ◽  
Vol 102 (C3) ◽  
pp. 5531-5551 ◽  
Author(s):  
Robert H. Tyler ◽  
Lawrence A. Mysak ◽  
Josef M. Oberhuber
Keyword(s):  
Electromagnetic Fields ◽  
Ocean Circulation ◽  
Three Dimensional ◽  
Global Ocean ◽  
Global Ocean Circulation

Eddy formation by dense flows on slopes in a rotating fluid

1998 ◽  
Vol 363 ◽  
pp. 229-252 ◽  
Author(s):  
GREGORY F. LANE-SERFF ◽  
PETER G. BAINES
Keyword(s):  
Ocean Circulation ◽  
Laboratory Experiments ◽  
Lower Layer ◽  
Ekman Layer ◽  
Global Ocean ◽  
Circulation System ◽  
Geostrophic Adjustment ◽  
Viscous Effects ◽  
Dense Fluid ◽  
Global Ocean Circulation

Properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments. The dense fluid may initially flow down the slope but it turns (under the influence of rotation) to flow along the slope, and initial geostrophic adjustment gives it an anticyclonic velocity profile. Some of the dense fluid drains downslope in a viscous Ekman layer, which may become unstable to growing waves. Provided that the viscous draining is not too strong, cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes. Three processes may contribute to the formation of these eddies. First, initial downslope flow of the dense current may stretch columns of ambient fluid by the ‘Taylor column’ process (which we term ‘capture’). Secondly, the initial geostrophic adjustment implies lower-layer collapse which may stretch the fluid column, and thirdly, viscous drainage will progressively stretch and spin up a captured water column. Overall this last process may be the most significant, but viscous drainage has contradictory effects, in that it progressively removes dense lower-layer fluid which terminates the process when the layer thickness approaches that of the Ekman layer. The eddies produced propagate along the slope owing to the combined effects of buoyancy–Coriolis balance and ‘beta-gyres’. This removes fluid from the vicinity of the source and causes the cycle to repeat. The vorticity of the upper-layer cyclones increases linearly with Γ=Lα/D (where L is the Rossby deformation radius, α the bottom slope and D the total depth), reaching approximately 2f in the experiments presented here. The frequency at which the eddy/dome structures are produced also increases with Γ, while the speed at which the structures propagate along the slope is reduced by viscous effects. The flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed.

scholarly journals Sustaining observations in the polar oceans

2014 ◽  
Vol 372 (2025) ◽  
pp. 20130337 ◽  
Author(s):  
E. P. Abrahamsen
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Ice Cover ◽  
Global Ocean ◽  
Shelf Seas ◽  
Polar Oceans ◽  
Global Ocean Circulation ◽  
Coordination And Collaboration ◽  
Temperature Depth

Polar oceans present a unique set of challenges to sustained observations. Sea ice cover restricts navigation for ships and autonomous measurement platforms alike, and icebergs present a hazard to instruments deployed in the upper ocean and in shelf seas. However, the important role of the poles in the global ocean circulation provides ample justification for sustained observations in these regions, both to monitor the rapid changes taking place, and to better understand climate processes in these traditionally poorly sampled areas. In the past, the vast majority of polar measurements took place in the summer. In recent years, novel techniques such as miniature CTD (conductivity–temperature–depth) tags carried by seals have provided an explosion in year-round measurements in areas largely inaccessible to ships, and, as ice avoidance is added to autonomous profiling floats and gliders, these promise to provide further enhancements to observing systems. In addition, remote sensing provides vital information about changes taking place in sea ice cover at both poles. To make these observations sustainable into the future, improved international coordination and collaboration is necessary to gain optimum utilization of observing networks.

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