Thermocline climatology of the Arabian Sea  -  a review

The monthly evolution of the thermocline characteristics for the Arabian Sea based on temperature profiles averaged over 2° × 2° grid cells is presented. During the pre-monsoon period, the entire Arabian Sea is characterized by a shallow thermocline (30–40 m) due to strong surface heating. Upwelling in the coastal regions and downwelling in the central Arabian Sea result in large variations in the thermocline topography during the south-west monsoon. This pattern reverses during winter when the surface currents reverse direction. The thermocline gradient is between 0.04°C m-1 and 0.14°C m-1 . An interesting result is the large variability in thermocline gradient (from 0.04°C m-1 near the coasts to 0.12°C m-1 in the central Arabian Sea) during July–September throughout the Arabian Sea. Weak gradients noticed in the northern Arabian Sea are due to the interaction of two different warm-water masses (the Arabian Sea and Persian Gulf water masses). The decrease in gradient in the equatorial Arabian Sea from January to June is attributed to the equatorial undercurrent which causes spreading of isotherms in the thermocline.

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Microseisms associated with disturbed weather in the Indian seas

Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character ◽

10.1098/rsta.1930.0008 ◽

1930 ◽

Vol 229 (670-680) ◽

pp. 287-328 ◽

Cited By ~ 18

Keyword(s):

North Atlantic ◽

Arabian Sea ◽

The State ◽

The South ◽

Monsoon Period ◽

The North ◽

Steady Vibrations ◽

South West Monsoon ◽

Seismic Records ◽

West Monsoon

Seismologists have often noted the appearance of pronounced microseisms in seismic records when the weather has been disturbed over a neighbouring sea. For instance, the late Dr. KLOTZ suggested a relationship between disturbed weather in the north Atlantic and the largest microseismic movements at Ottawa. Dr. HARRISON, writing in ' Nature,’ November 1, 1924, in continuation of a note* by the present writer, pointed out that well-marked microseisms in the Omori charts at Calcutta invariably confirmed other evidence in the case of the early stages of dangerous cyclones, and were sometimes noticed when the storm centre was so much as 1000 miles south of Calcutta. He did not, however, recall any instance in which microseisms were associated with ordinary rough weather or with an advance of the monsoon. On the other hand, “ investigation at Eskdalemuir of the possible connection between microseismical amplitude and the state of the sea at different points of the British coasts have yielded results of an inconclusive kind. For example, the correlation between the state of the sea and the Microseismic movements of a type, which were quite characteristic of the south-west monsoon period, made their first appearance in the seismograms generally in May with the advance of the monsoon in the south-east Arabian Sea, becoming more and more pronounced as the monsoon currents approached Bombay. They became less marked or disappeared during a temporary break in the monsoon and reappeared with the strengthening of the currents. They were more or less steady vibrations having periods ranging from 4 to 10 seconds.

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

Ocean Science ◽

10.5194/os-11-667-2015 ◽

2015 ◽

Vol 11 (5) ◽

pp. 667-693 ◽

Cited By ~ 21

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.

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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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