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

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.

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

Ocean Science Discussions ◽

10.5194/osd-12-493-2015 ◽

2015 ◽

Vol 12 (2) ◽

pp. 493-550 ◽

Cited By ~ 1

Author(s):

P. L'Hégaret ◽

R. Duarte ◽

X. Carton ◽

C. Vic ◽

D. Ciani ◽

...

Keyword(s):

Persian Gulf ◽

Seasonal Variability ◽

Arabian Sea ◽

Meteorological Data ◽

Mesoscale Eddies ◽

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 the monsoon forcing, reveal a strong seasonal variability and intense mesoscale features. We describe and analyse this variability and these features, using both meteorological data (from ECMWF reanalyses), in-situ observations (from the ARGO float program and the GDEM climatology), satellite altimetry (from AVISO) and a regional simulation with a primitive equation model (HYCOM). The EOFs of the seasonal variability of the water masses quantify their main changes in thermohaline characteristics and in position. The model and observations display comparable variability, and the model is then used to analyse the three-dimensional structure of eddies and water masses with a higher resolution. 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. This water mass is also captured inside the eddies via several mechanisms, keeping high thermohaline characteristics in the Arabian Sea. These characteristics are validated on the GOGP99 cruise data.

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Mesoscale eddies and submesoscale structures of Persian Gulf Water off the Omani coast in spring 2011

Ocean Science ◽

10.5194/os-12-687-2016 ◽

2016 ◽

Vol 12 (3) ◽

pp. 687-701 ◽

Cited By ~ 18

Author(s):

Pierre L'Hégaret ◽

Xavier Carton ◽

Stephanie Louazel ◽

Guillaume Boutin

Keyword(s):

Persian Gulf ◽

Arabian Sea ◽

Cold Water ◽

Mesoscale Eddies ◽

High Salinity Water ◽

Strait Of Hormuz ◽

Persian Gulf Water ◽

Salinity Water ◽

The Persian Gulf ◽

Sea Of Oman

Abstract. The Persian Gulf produces high-salinity water (Persian Gulf Water, PGW hereafter), which flows into the Sea of Oman via the Strait of Hormuz. Beyond the Strait of Hormuz, the PGW cascades down the continental slope and spreads in the Sea of Oman under the influence of the energetic mesoscale eddies. The PGW outflow has different thermohaline characteristics and pathways, depending on the season. In spring 2011, the Phys-Indien experiment was carried out in the Arabian Sea and in the Sea of Oman. The Phys-Indien 2011 measurements, as well as satellite observations, are used here to characterize the circulation induced by the eddy field and its impact on the PGW pathway and evolution. During the spring intermonsoon, an anticyclonic eddy is often observed at the mouth of the Sea of Oman. It creates a front between the eastern and western parts of the basin. This structure was observed in 2011 during the Phys-Indien experiment. Two energetic eddies were also present along the southern Omani coast in the Arabian Sea. At their peripheries, ribbons of freshwater and cold water were found due to the stirring created by the eddies. The PGW characteristics are strongly influenced by these eddies. In the western Sea of Oman, in 2011, the PGW was fragmented into filaments and submesoscale eddies. It also recirculated locally, thus creating salty layers with different densities. In the Arabian Sea, a highly saline submesoscale lens was recorded offshore. Its characteristics are analyzed here and possible origins are proposed. The recurrence of such lenses in the Arabian Sea is also briefly examined.

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Mesoscale eddies and submesoscale structures of Persian Gulf Water off the Omani coast in Spring 2011

Ocean Science Discussions ◽

10.5194/osd-12-2743-2015 ◽

2015 ◽

Vol 12 (6) ◽

pp. 2743-2782

Author(s):

P. L'Hégaret ◽

X. Carton ◽

S. Louazel ◽

G. Boutin

Keyword(s):

Persian Gulf ◽

Arabian Sea ◽

High Salinity ◽

Cold Water ◽

Mesoscale Eddies ◽

High Salinity Water ◽

Persian Gulf Water ◽

Salinity Water ◽

The Persian Gulf ◽

Sea Of Oman

Abstract. The Persian Gulf produces a high salinity water (Persian Gulf Water, PGW hereafter) flowing into the Sea of Oman, in the northwestern Indian Ocean. Past the Strait of Hormuz, the PGW cascades down the continental slope and spreads in the Sea of Oman under the influence of the energetic mesoscale eddies with different thermohaline signatures and pathways depending of the season. In spring 2011, the Phys-Indien experiment was carried out in the Arabian Sea an in the Sea of Oman. This study uses the results from the measurements to characterize the water masses, their thermohaline and dynamical signatures. During the spring intermonsoon, an anticyclonic eddy is often observed at the mouth of the Sea of Oman. This structure was present in 2011 and created a front between the eastern and western part of the basin. As well two energetic gyres were present along the Omani coast in the Arabian Sea. At their peripheries, injections of fresh and cold water are found in relation with the stirring of the eddies. The PGW observed below or between these eddies have a different dilution depending of the position and formation periods of the gyres. Furthermore, in the western Sea of Oman, the PGW is fragmented in filaments and submesoscale eddies. As well, recirculation of the PGW is observed, thus having the presence of salty nearby patches with two densities. Offshore, in the Arabian Sea, a submesoscale lens was recorded. The different mechanisms leading to its formation and presence are assessed here.

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The life cycle of submesoscale eddies generated by topographic interactions

10.5194/os-2019-3 ◽

2019 ◽

Author(s):

Mathieu Morvan ◽

Pierre L'Hégaret ◽

Xavier Carton ◽

Jonathan Gula ◽

Clément Vic ◽

...

Keyword(s):

Life Cycle ◽

Red Sea ◽

Persian Gulf ◽

Sea Water ◽

Mesoscale Eddies ◽

Shear Instability ◽

Gulf Of Oman ◽

Coherent Vortices ◽

Persian Gulf Water ◽

The Persian Gulf

Abstract. The Persian Gulf Water and Red Sea Water are salty and dense waters recirculating at subsurface in the Gulf of Oman and the Gulf of Aden respectively, under the influence of mesoscale eddies which dominate the surface flow in both semi-enclosed basins. In situ measurements combined with altimetry indicate that the Persian Gulf Water is driven by mesoscale eddies in the form of filaments and submesoscale structures. In this paper, we study the formation and the life cycle of intense submesoscale vortices and their impact on the spread of Persian Gulf Water and Red Sea Water. We use a three-dimensional hydrostatic model with submesoscale-resolving resolution to study the evolution of submesoscale vortices. Our configuration is an idealized version of the Gulf of Oman and Aden: a zonal row of mesoscale vortices interacting with north and south topographic slopes. Intense submesoscale vortices are generated in the simulations along the continental slopes due to two different mechanisms. The first mechanism is due to frictional generation of vorticity in the bottom boundary layer, which detaches from the topography, forms an unstable vorticity filament, and undergoes horizontal shear instability that leads to the formation of submesoscale coherent vortices. The second mechanism is inviscid and implies arrested topographic Rossby waves breaking and forming submesoscale coherent vortices where a mesoscale anticyclone interacts with the topographic slope. Submesoscale vortices subsequently drift away, merge and form larger vortices. They can also pair with opposite signed vortices and travel across the domain. They can weaken or disappear via several mechanisms, in particular fusion into the larger eddies or erosion on the topography. Particle patches are advected and sheared by vortices and are entrained into filaments. Their size first grows as the square root of time, a signature of the merging processes, then it increases linearly with time, corresponding to their ballistic advection by submesoscale eddies. On the contrary, witout intense submesoscale eddies, particles are mainly advected by mesoscale eddies; this implies a weaker dispersion of particles than in the previous case. This shows the important role of submesoscale eddies in spreading Persian Gulf Water and Red Sea Water.

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Mesoscale variability of water masses in the Arabian Sea as revealed by ARGO floats

Ocean Science ◽

10.5194/os-8-227-2012 ◽

2012 ◽

Vol 8 (2) ◽

pp. 227-248 ◽

Cited By ~ 17

Author(s):

X. Carton ◽

P. L'Hegaret ◽

R. Baraille

Keyword(s):

Arabian Sea ◽

Regional Scale ◽

Water Masses ◽

Gulf Of Aden ◽

Mesoscale Variability ◽

Energy Distributions ◽

Sea Level Anomaly ◽

Persian Gulf Water ◽

The Persian Gulf ◽

Anomalous Water

Abstract. By analysing ARGO float data over the last four years, a few aspects of the mesoscale variability of water masses in the Arabian Sea are described. The Red Sea Outflow Water (RSOW) is concentrated in the Southwestern Gulf of Aden, in particular when a cyclonic gyre predominates in this region. Salinities of 36.5 and temperatures of 16 °C are found in this area at depths between 600 and 1000 m. RSOW is more dilute in the eastern part of the Gulf, where intense and relatively barotropic gyres mix it with Indian ocean Central Water. RSOW is also detected along the northeastern coast of Socotra, and fragments of RSOW are found between one and three degrees of latitude north of this island. In the whole Gulf of Aden, the correlation between the deep motions of the floats and the sea-level anomaly measured by altimetry is strong, at regional scale. The finer scale details of the float trajectories are not sampled by altimetry and are often related to the anomalous water masses that the floats encounter. The Persian Gulf Water (PGW) is found in the float profiles near Ras ash Sharbatat (near 57° E, 18° N), again with 36.5 in salinity and about 18–19 °C in temperature. These observations were achieved in winter when the southwestward monsoon currents can advect PGW along the South Arabian coast. Fragments of PGW were also observed in the Arabian Sea between 18 and 20° N and 63 and 65° E in summer, showing that this water mass can escape the Gulf of Oman southeastward, during that season. Kinetic energy distributions of floats with respect to distance or angle share common features between the two regions (Gulf of Aden and Arabian Sea), in particular peaks at 30, 50 and 150 km scales and along the axis of monsoon currents. Hydrological measurements by floats are also influenced by the seasonal variations of PGW and RSOW in these regions.

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NUMERICAL SIMULATION OF TROPICAL CYCLONES AND STORM SURGES IN THE ARABIAN SEA

Coastal Engineering Proceedings ◽

10.9753/icce.v36.papers.11 ◽

2018 ◽

pp. 11

Author(s):

Mohsen Soltanpour ◽

Zahra Ranji ◽

Tomoyo Shibayama ◽

Sarmad Ghader ◽

Shinsaku Nishizaki

Keyword(s):

Tropical Cyclones ◽

Persian Gulf ◽

Arabian Sea ◽

Storm Surges ◽

Ocean Model ◽

Gulf Of Oman ◽

The Persian Gulf ◽

The Impact ◽

Landfall Location ◽

Good Agreement

Winds, waves and storm surges of Gonu and Ashobaa, as two recent cyclones in the Arabian Sea and Gulf of Oman, are simulated by a system of WRF-FVCOM-SWAN. The employed models are separately calibrated using the available data. Surges are found to be highly dependent on coastal geometry and landfall location, rather than the storm intensity. Comparisons at different stations reveal that the results of models are in a good agreement with measured parameters. Negative surges are also observed in the enclosed basins of the Persian Gulf and Red Sea. The calibrated atmosphere-wave-ocean model can be utilized for the prediction of extreme events, expected to increase in future due to the impact of the climate change.

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A Modeling Study of Circulation and Eddies in the Persian Gulf

Journal of Physical Oceanography ◽

10.1175/2010jpo4227.1 ◽

2010 ◽

Vol 40 (9) ◽

pp. 2122-2134 ◽

Cited By ~ 48

Author(s):

Prasad G. Thoppil ◽

Patrick J. Hogan

Keyword(s):

Persian Gulf ◽

Spatial Scales ◽

Baroclinic Instability ◽

Mesoscale Eddies ◽

Ocean Model ◽

Coastal Current ◽

Basin Scale ◽

Strait Of Hormuz ◽

Moderate Resolution Imaging Spectroradiometer ◽

The Persian Gulf

Abstract The circulation and mesoscale eddies in the Persian Gulf are investigated using results from a high-resolution (∼1 km) Hybrid Coordinate Ocean Model (HYCOM). The circulation in the Persian Gulf is composed of two spatial scales: basin scale and mesoscale. The progression of a cyclonic circulation cell dominates the basin-scale circulation in the eastern half of the gulf (52°–55°E) during March–July. This is primarily the consequence of density-driven outflow–inflow through the Strait of Hormuz and strong stratification. A northwestward-flowing Iranian Coastal Current (ICC; 30–40 cm s−1) between the Strait of Hormuz and north of Qatar (∼52°E) forms the northern flank of the cell. Between July and August the ICC becomes unstable because of the baroclinic instability mechanism by releasing the potential energy stored in the cross-shelf density gradient. As a result, the meanders in the ICC evolve into a series of mesoscale eddies, which is denoted as the Iranian coastal eddies (ICE). The ICE have a diameter of about 115–130 km and extend vertically over most of the water column. Three cyclonic eddies produced by the model during August–September 2005 compared quite well with the Moderate Resolution Imaging Spectroradiometer (MODIS) SST and chlorophyll-a observations. The remnants of ICE are seen until November, after which they dissipate as the winter cooling causes the thermocline to collapse.

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Ventilation dynamics of the Oxygen Minimum Zone in the Arabian Sea

10.5194/bg-2019-168 ◽

2019 ◽

Author(s):

Henrike Schmidt ◽

Rena Czeschel ◽

Martin Visbeck

Keyword(s):

Summer Monsoon ◽

Persian Gulf ◽

Arabian Sea ◽

Sea Water ◽

Ocean Model ◽

Western Basin ◽

Eastern Basin ◽

Persian Gulf Water ◽

Core Thickness ◽

Oxygen Minimum

Abstract. Oxygen minimum zones (OMZs) in the open ocean occur below the surface in regions of weak ventilation and high biological productivity. Very low levels of dissolved oxygen affect marine life and alter biogeochemical cycles. One of the most intense but least understood OMZs in the world is located in the Arabian Sea in a depth range between 300 to 1000 m. Within the last decades observations suggest a decreasing oxygen trend. Thus, an improved understanding of the crucial processes is necessary for a reliable assessment of the future development of the Arabian Sea OMZ. This study uses a combination of observational data as well as reanalysis velocity fields from the ocean model Hycom (Hybrid Coordinate Ocean Model) to explore the ventilation dynamics of the Arabian Sea OMZ. Our results show that the OMZ features a strong seasonal cycle with regional differences that is correlated with the monsoon system: In the eastern basin, the OMZ is strongest during the winter monsoon with a core thickness of 1000 m depth and oxygen values of less than 5 µmol/kg. Ventilation during that phase is dominated by Persian Gulf water, that clockwise circles the perimeter of the basin and enters the OMZ from the north. During the summer monsoon ventilation from the southeast leads to higher oxygen values indicating a reverse flow along the Indian coast in the intermediate layer compared to the southeastward surface currents. The seasonal cycle in the western basin has the same seasonality as the one in the eastern basin with a core thickness of 900 m during the winter monsoon. The oxygen supply during the summer monsoon is weaker compared to the eastern basin and correlates with the ventilation of Persian Gulf (Red Sea) water during the summer monsoon (autumn inter-monsoon) phase. As the interior exchange between the eastern and western basin is weak, the more pronounced OMZ in the eastern basin is explained by prolonged ventilation time scales. For the eastern (western) basin Persian Gulf water needs 2–3 (1–2) years and Red Sea water 7–8 (3–4) years to ventilate the OMZ.

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