scholarly journals Structure and Dynamics of the Ras al Hadd Oceanic Dipole in the Arabian Sea

Oceans ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 105-125
Author(s):  
Adam Ayouche ◽  
Charly De Marez ◽  
Mathieu Morvan ◽  
Pierre L’Hegaret ◽  
Xavier Carton ◽  
...  
Keyword(s):  
Process Model ◽  
Model Simulation ◽  
Ocean Model ◽  
Tracking Algorithm ◽  
Detection And Tracking ◽  
Hybrid Coordinate Ocean Model ◽  
Persian Gulf Water ◽  
The Persian Gulf ◽  
Water Outflow ◽  
Eddy Detection

The Ras al Hadd oceanic dipole is a recurrent association of a cyclone (to the northeast) and of an anticyclone (to the southwest), which forms in summer and breaks up at the end of autumn. It lies near the Ras al Hadd cape, southeast of the Arabian peninsula. Its size is on the order of 100 km. Along the axis of this dipole flows an intense jet, the Ras al Had jet. Using altimetric data and an eddy detection and tracking algorithm (AMEDA: Angular Momentum Eddy Detection and tracking Algorithm), we describe the life cycle of this oceanic dipole over a year (2014–2015). We also use the results of a numerical model (HYCOM, the HYbrid Coordinate Ocean Model) simulation, and hydrological data from ARGO profilers, to characterize the vertical structure of the two eddies composing the dipole, and their variability over a 15 year period. We show that (1) before the dipole is formed, the two eddies that will compose it, come from different locations to join near Ras al Hadd, (2) the dipole remains near Ras al Hadd during summer and fall while the wind stress (due to the summer monsoon wind) intensifies the cyclone, (3) both the anticyclone and the cyclone reach the depth of the Persian Gulf Water outflow, and (4) their horizontal radial velocity profile is often close to Gaussian but it can vary as the dipole interacts with neighboring eddies. As a conclusion, further work with a process model is recommended to quantify the interaction of this dipole with surrounding eddies and with the atmosphere.

On the Mechanisms of Episodic Salinity Outflow Events in the Strait of Hormuz

2009 ◽  
Vol 39 (6) ◽  
pp. 1340-1360 ◽  
Author(s):  
Prasad G. Thoppil ◽  
Patrick J. Hogan
Keyword(s):  
Wind Stress ◽  
Ocean Model ◽  
Barotropic Instability ◽  
Translation Speed ◽  
Velocity Fluctuations ◽  
Continuous Formation ◽  
Hybrid Coordinate Ocean Model ◽  
Strait Of Hormuz ◽  
Persian Gulf Water ◽  
Lateral Mixing

Abstract Observations in the Strait of Hormuz (26.26°N, 56.08°E) during 1997–98 showed substantial velocity fluctuations, accompanied by episodic changes in the salinity outflow events with amplitude varying between 1 and 2 psu on time scales of several days to a few weeks. These events are characterized by a rapid increase in salinity followed by an abrupt decline. The mechanisms behind these strong pulses of salinity events are investigated with a high-resolution (∼1 km) Hybrid Coordinate Ocean Model (HYCOM) with particular reference to the year 2005. In accordance with the observations, the simulated salinity events are characterized by strong coherence between the enhanced flows in zonal and meridional directions. It is inferred that most of the simulated and observed outflow variability is associated with the continuous formation of strong mesoscale cyclonic eddies, whose origin can be traced upstream to around 26°N, 55.5°E. These cyclonic eddies have a diameter of about 63 km and have a remnant of Persian Gulf water (PGW) in their cores, which is eroded by lateral mixing as the eddies propagate downstream at a translation speed of 4.1 cm s−1. The primary process that acts to generate mesoscale cyclones results from the barotropic instability of the exchange circulation through the Strait of Hormuz induced by fluctuations in the wind stress forcing. The lack of salinity events and cyclogenesis in a model experiment with no wind stress forcing further confirms the essential ingredients required for the development of strong cyclones and the associated outflow variability.

scholarly journals Mesoscale variability in the Arabian Sea from HYCOM model results and observations: impact on the Persian Gulf Water path

Ocean Science ◽  
2015 ◽  
Vol 11 (5) ◽  
pp. 667-693 ◽  
Author(s):  
P. L'Hégaret ◽  
R. Duarte ◽  
X. Carton ◽  
C. Vic ◽  
D. Ciani ◽  
...  
Keyword(s):  
Persian Gulf ◽  
Arabian Sea ◽  
Meteorological Data ◽  
Mesoscale Eddies ◽  
Ocean Model ◽  
Water Masses ◽  
Dimensional Structure ◽  
Persian Gulf Water ◽  
The Persian Gulf ◽  
Sea Of Oman

Abstract. The Arabian Sea and Sea of Oman circulation and water masses, subject to monsoon forcing, reveal a strong seasonal variability and intense mesoscale features. We describe and analyze this variability and these features, using both meteorological data (from ECMWF reanalyses), in situ observations (from the ARGO float program and the GDEM – Generalized Digital Environmental mode – climatology), satellite altimetry (from AVISO) and a regional simulation with a primitive equation model (HYCOM – the Hybrid Coordinate Ocean Model). The model and observations display comparable variability, and the model is then used to analyze the three-dimensional structure of eddies and water masses with higher temporal and spatial resolutions than the available observations. The mesoscale features are highly seasonal, with the formation of coastal currents, destabilizing into eddies, or the radiation of Rossby waves from the Indian coast. The mesoscale eddies have a deep dynamical influence and strongly drive the water masses at depth. In particular, in the Sea of Oman, the Persian Gulf Water presents several offshore ejection sites and a complex recirculation, depending on the mesoscale eddies. The associated mechanisms range from coastal ejection via dipoles, alongshore pulses due to a cyclonic eddy, to the formation of lee eddies downstream of Ra's Al Hamra. This water mass is also captured inside the eddies via several mechanisms, keeping high thermohaline characteristics in the Arabian Sea. The variations of the outflow characteristics near the Strait of Hormuz are compared with variations downstream.

scholarly journals Evaluating two numerical advection schemes in HYCOM for eddy-resolving modelling of the Agulhas Current

Ocean Science ◽  
2009 ◽  
Vol 5 (2) ◽  
pp. 173-190 ◽  
Author(s):  
B. C. Backeberg ◽  
L. Bertino ◽  
J. A. Johannessen
Keyword(s):  
Vertical Structure ◽  
Model Simulation ◽  
Current System ◽  
Ocean Model ◽  
Sea Surface ◽  
Agulhas Current ◽  
Implementation Model ◽  
Advection Scheme ◽  
Hybrid Coordinate Ocean Model ◽  
Advection Schemes

Abstract. A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions.

scholarly journals Angular Momentum Eddy Detection and Tracking Algorithm (AMEDA) and Its Application to Coastal Eddy Formation

2018 ◽  
Vol 35 (4) ◽  
pp. 739-762 ◽  
Author(s):  
Briac Le Vu ◽  
Alexandre Stegner ◽  
Thomas Arsouze
Keyword(s):  
Angular Momentum ◽  
Velocity Field ◽  
Dynamical Evolution ◽  
Mesoscale Eddies ◽  
Velocity Fields ◽  
Tracking Algorithm ◽  
Fine Tuning ◽  
Surface Velocity ◽  
Detection And Tracking ◽  
Eddy Detection

AbstractAutomated methods are important for the identification of mesoscale eddies in the large volume of oceanic data provided by altimetric measurements and numerical simulations. This paper presents an optimized algorithm for detecting and tracking eddies from two-dimensional velocity fields. This eddy identification uses a hybrid methodology based on physical parameters and geometrical properties of the velocity field, and it can be applied to various fields having different spatial resolutions without a specific fine-tuning of the parameters. The efficiency and the robustness of the angular momentum eddy detection and tracking algorithm (AMEDA) was tested with three different types of input data: the 1/8° Archiving, Validation, and Interpretation of Satellite Oceanographic Data (AVISO) geostrophic velocity fields available for the Mediterranean Sea; the output of the idealized Regional Ocean Modeling System numerical model; and the surface velocity field obtained from particle imagery on a rotating tank experiment. All these datasets describe the dynamical evolution of mesoscale eddies generated by the instability of a coastal current. The main advantages of AMEDA are as follows: the algorithm is robust to the grid resolution, it uses a minimal number of tunable parameters, the dynamical features of the detected eddies are quantified, and the tracking procedure identifies the merging and splitting events. The proposed method provides a complete dynamical evolution of the detected eddies during their lifetime. This allows for identifying precisely the formation areas of long-lived eddies, the region where eddy splitting or merging occurs frequently, and the interaction between eddies and oceanic currents.

scholarly journals Evaluating two numerical advection schemes in HYCOM for eddy-resolving modelling of the Agulhas Current

2009 ◽  
Vol 6 (1) ◽  
pp. 429-475 ◽  
Author(s):  
B. C. Backeberg ◽  
L. Bertino ◽  
J. A. Johannessen
Keyword(s):  
Vertical Structure ◽  
Model Simulation ◽  
Current System ◽  
Ocean Model ◽  
Sea Surface ◽  
Agulhas Current ◽  
Implementation Model ◽  
Advection Scheme ◽  
Hybrid Coordinate Ocean Model ◽  
Advection Schemes

Abstract. A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the Southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and Southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions.

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