Circulation and water masses of the Arabian Sea
ABSTRACT The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related
annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted
for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface
regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing
due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent
studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating
along the west coast of India.
The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary
current. Local wind-driving is also important to the coastal circulation off western India during the southwest monsoon but
not during the northeast monsoon when a strong (approximately 7 × 106m3/sec) current moves poleward against weak winds. This current is driven by a pressure gradient which forms along this coast
during the northeast monsoon due to either thermohaline-forcing or due to the arrival of Kelvin waves from the Bay of Bengal.
The present speculation about flow of bottom water (deeper than about 3500 m) in the Arabian Sea is that it moves northward
and upwells into the layer of North Indian Deep Water (approximately 1500–3500m). It is further speculated that the flow in
this layer consists of a poleward western boundary current and a weak equatorward flow in the interior. It is not known if
there is an annual cycle associated with the deep and the bottom water circulation.
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ABSTRACT: Sea Surface Height (SSH) variability in the Indian Ocean during 1993-1995 is studied using TOPEX/POSEIDON (T/P) altimetry data. Strong interannual variability is seen in the surface circulation of the western Arabian Sea, especially in the Somali eddy structure. During the Southwest (SW) monsoon, a weak monsoon year is characterized by a single eddy system off Somalia, a strong or normal monsoon year by several energetic eddies. The Laccadive High (LH) and Laccadive Low (LL) systems off southwest India are observed in the altimetric SSH record. The variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal, is also detected. Evidence is found for the propagation of Kelvin and Rossby waves across the northern Indian Ocean; these are examined in the context of energy transfer to the western boundary currents, and associated eddies. A simple wind-driven isopycnal model having three active layers is implemented to simulate the seasonal changes of surface and subsurface circulation in the North Indian Ocean and to examine the response to different wind forcing. The wind forcing is derived from the ERS-1 scatterometer wind stress for the same period as the T/P altimeter data, enabling the model response in different (active/weak) monsoon conditions to be tested. The model output is derived in 10-day snapshots to match the time period of the T/P altimeter cycles. Complex Principal Component Analysis (CPCA) is applied to both altimetric and model SSH data. This confirms that long Rossby waves are excited by the remotely forced Kelvin waves off the southwest coast of India and contribute substantially to the variability of the seasonal circulation in the Arabian Sea.Marine Geodesy 01/2000; 23(3). DOI:10.1080/01490410050128609 · 1.12 Impact Factor
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ABSTRACT: We use data from six Acoustic Doppler Current Profiler (ADCP) moorings deployed during March-September 2008 on the continental shelf and slope off Bhatkal, Goa, and Jaigarh on the central west coast of India to present evidence for poleward propagation of shelf or coastal-trapped waves (CTWs). Wave propagation is seen on the shelf in the 20-40-day, 10-14-day, and 3-5-day-period bands. The lag from south to north indicates that remote forcing is important even at periods as short as 4 days. Using QuikSCAT wind data, we show that the contribution of remote forcing to the shelf West Indian Coastal Current (WICC) is significant even when the local alongshore wind is strong, as during the summer-monsoon onset during May-June, and forces a strong local response that masks the effect of remote forcing. Forced wave calculations using CTW theory show that remote forcing of the WICC is present at all times, but is most striking when the local winds are weak, as during March-April. The CTW calculations show that the source region for the remote forcing may extend beyond the west coast into the Gulf of Mannar between India and Sri Lanka. On the slope, propagation is seen only at the 4-day period. At higher periods, the slope WICC decorrelates rapidly along the coast, but upward phase propagation, implying downward propagation of energy associated with poleward propagation, is evident even at these higher periods.05/2012; 117(C5):5017-. DOI:10.1029/2011JC007606
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ABSTRACT: Monthly coastal sampling and ship-cruise-measured in situ datasets of nitrate, sea surface temperature (SST), and chlorophyll in the SW Bay of Bengal covering Tamilnadu and Andhra Pradesh coasts of India were used to develop nitrate algorithm. A total of 15 datasets prepared during 2009–11 covered cruise data and all monthly datasets, nine datasets followed with better results with paraboloid function, and others followed linear, Gaussian, and Lorentzian function regression fits. Data collection through cruises (397 points), monthly (482 points) coastal sampling, total monthly and cruise (879 points) covering four seasons were used, and the three-dimensional (3D)-paraboloid function showed better results during the seasonal scale study with the R2 values 0.670, 0.635, 0.465, and 0.693 for the postmonsoon, summer, premonsoon, and monsoon seasons respectively. In the current study, there has been considerable improvement in R2 (0.670 with 236 points) than the earlier study using postmonsoon data (0.560 with 105 data points). Through this algorithm, a nitrate map was generated for 11 March 2011 using Oceansat-2 Ocean Color Monitor (OCM) and MODIS-aqua-derived chlorophyll and SST data, respectively. The retrieved nitrate map has been validated with in situ dataset of the same date with an R2 value of 0.718, which suggests that the developed nitrate algorithm was statistically significant with mean normalized bias (MNB) ¼ 0.078, root mean square error (RMSE) ¼ 0.412, and standard error of estimate (SEE)¼60.4032, and the algorithm was observed to be working satisfactorily over the SW Bay of Bengal region.Journal of Coastal Research 01/2015; 31(2):398-406. DOI:10.2112/JCOASTRES-D-12-00270.1 · 0.76 Impact Factor