‘Thermohaline front’ off the east coast of India and its generating mechanism

Kumar, P. V. Hareesh; Mathew, Basil; Kumar, M. R. Ramesh; Rao, A. Raghunadha; Jagadeesh, P. S. V.; Radhakrishnan, K. G.; Shyni, T. N.

doi:10.1007/s10236-013-0652-y

Cited by 19 publications

(14 citation statements)

References 18 publications

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“…The results above clearly demonstrate the large‐scale remote IOD influence on postmonsoon coastal freshening along the east coast of India. However, Figure also reveals smaller‐scale SSS features in regions of strong gradients, which were previously linked with mesoscale oceanic eddies (e.g., Babu et al, ; Hareesh Kumar et al, ; Murty et al, ). To relate these smaller‐scale SSS features with mesoscale eddy variability, Figures a and b display the SLA anomalies with respect to the mean seasonal cycle in October 2015 and 2016 (Figures and for September and November months, and Figure for a zoom of SSS and currents).…”

Section: Resultssupporting

confidence: 57%

“…Shetye et al () documented such a narrow coastal freshwater plume southwest of the GB mouth based on in situ observations collected during a cruise in December 1991, with an 8 pss drop over 100 km toward offshore at 12°N near the Indian coast. Hareesh Kumar et al () also used in situ measurements to highlight a strong thermohaline front off the east coast of India in December 1997, with an offshore meandering due to mesoscale eddies. Recently, Chaitanya et al () used in situ observations collected by fishermen along the east coast of India to demonstrate that this ∼200 km wide freshwater tongue (referred to as a “river in the sea”) is a seasonally recurring feature, whose expansion is coincidental with the development of the southward‐flowing EICC.…”

Section: Introductionmentioning

confidence: 99%

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Modulation of the Ganges‐Brahmaputra River Plume by the Indian Ocean Dipole and Eddies Inferred From Satellite Observations

Fournier

Vialard

Lengaigne³

et al. 2017

JGR Oceans

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The Bay of Bengal receives large amounts of freshwater from the Ganga‐Brahmaputra (GB) river during the summer monsoon. The resulting upper‐ocean freshening influences seasonal rainfall, cyclones, and biological productivity. Sparse in situ observations and previous modeling studies suggest that the East India Coastal Current (EICC) transports these freshwaters southward after the monsoon as an approximately 200 km wide, 2,000 km long “river in the sea” along the East Indian coast. Sea surface salinity (SSS) from the Soil Moisture Active Passive (SMAP) satellite provides unprecedented views of this peculiar feature from intraseasonal to interannual timescales. SMAP SSS has a 0.83 correlation and 0.49 rms‐difference to 0–5 m in situ measurements. SMAP and in stu data both indicate a SSS standard deviation of ∼0.7 to 1 away from the coast, that rises to 2 pss within 100 km of the coast, providing a very favorable signal‐to‐noise ratio in coastal areas. SMAP also captures the strong northern BoB, postmonsoon cross‐shore SSS contrasts (∼10 pss) measured along ship transects. SMAP data are also consistent with previous modeling results that suggested a modulation of the EICC/GB plume southward extent by the Indian Ocean Dipole (IOD). Remote forcing associated with the negative Indian Ocean Dipole in the fall of 2016 indeed caused a stronger EICC and “river in the sea” that extended by approximately 800 km further south than that in 2015 (positive IOD year). The combination of SMAP and altimeter data shows eddies stirring the freshwater plume away from the coast.

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Section: Resultssupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Modulation of the Ganges‐Brahmaputra River Plume by the Indian Ocean Dipole and Eddies Inferred From Satellite Observations

Fournier

Vialard

Lengaigne³

et al. 2017

JGR Oceans

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“…The western rim of the BoB is an area of intense eddy activity [ Durand et al ., 2009]. Our model is eddy‐permitting, but not really eddy‐resolving, and does not permit assessing the effect of the oceanic mesoscale circulation on the coastal freshwater strip, which is probably strong [e.g., Hareesh Kumar et al ., ]. Refining the model resolution may therefore also be a way to further improve the realism of our simulation.…”

Section: Discussionmentioning

confidence: 99%

“…; Akhil et al ., ; Benshila et al ., ]. Recent observations [ Chaitanya et al ., ; Hareesh Kumar et al ., ] and historical cruise data [ Shetye et al ., ] indicate that the seasonal freshening along the East Indian coast occurs in a narrow (∼100 km wide) band with coastal waters up to 10 pss fresher than those offshore, a feature that has been dubbed “the river in the sea” [ Chaitanya et al . ].…”

Section: Introductionmentioning

confidence: 99%

“…The southward expansion of fresh water along the east coast of India in fall has been further attributed to horizontal advection of fresh waters from the northern BoB by the southward-flowing EICC Akhil et al, 2014;Benshila et al, 2014]. Recent observations Hareesh Kumar et al, 2013] and historical cruise data indicate that the seasonal freshening along the East Indian coast occurs in a narrow (100 km wide) band with coastal waters up to 10 pss fresher than those offshore, a feature that has been dubbed ''the river in the sea'' . While the southward expansion of this ''river in the sea'' is attributed to horizontal advection by the EICC, its erosion occurs prominently through vertical exchanges of salt at the bottom of the mixed layer [Akhil et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

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A modeling study of processes controlling the Bay of Bengal sea surface salinity interannual variability

Akhil

Lengaigne

Vialard

et al. 2016

J. Geophys. Res. Oceans

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Recent observational studies provided preliminary insights on the interannual variability of Bay of Bengal (BoB) Sea Surface Salinity (SSS), but are limited by the poor data coverage. Here, we describe the BoB interannual SSS variability and its driving processes from a regional eddy‐permitting ocean general circulation model forced by interannually varying air‐sea fluxes and altimeter‐derived discharges of major rivers over the past two decades. Simulated interannual SSS variations compare favorably with both in situ and satellite data and are largest in boreal fall in three regions: the northern BoB, the coastal region off east India, and the Andaman Sea. In the northern BoB, these variations are independent from those in other regions and mostly driven by summer‐fall Ganga‐Brahmaputra runoff interannual variations. In fall, remote forcing from the Indian Ocean Dipole results in anticlockwise anomalous horizontal currents that drive interannual SSS variations of opposite polarity along the east coast of India and in the Southern Andaman Sea. From winter onward, these anomalies are damped by vertical mixing in the northern BoB and along the east coast of India and by horizontal advection in the Southern Andaman Sea. While river runoff fluctuations locally play a strong role near the Ganga‐Brahmaputra river mouth, wind‐driven interannual current anomalies are responsible for a large fraction of SSS interannual variability in most of the basin.

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A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal

et al. 2014

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In response to the Indian Monsoon freshwater forcing, the Bay of Bengal exhibits a very strong seasonal cycle in sea surface salinity (SSS), especially near the mouths of the Ganges-Brahmaputra and along the east coast of India. In this paper, we use an eddy-permitting (25 km resolution) regional ocean general circulation model simulation to quantify the processes responsible for this SSS seasonal cycle. Despite the absence of relaxation toward observations, the model reproduces the main features of the observed SSS seasonal cycle, with freshest water in the northeastern Bay, particularly during and after the monsoon. The model also displays an intense and shallow freshening signal in a narrow (100 km wide) strip that hugs the east coast of India, from September to January, in good agreement with high-resolution measurements along two ships of opportunity lines. The mixed layer salt budget confirms that the strong freshening in the northern Bay during the monsoon results from the Ganges-Brahmaputra river discharge and from precipitation over the ocean. From September onward, the East India Coastal Current transports this freshwater southward along the east coast of India, reaching the southern tip of India in November. The surface freshening results in an enhanced vertical salinity gradient that increases salinity of the surface layer by vertical processes. Our results reveal that the erosion of the freshwater tongue along the east coast of India is not driven by northward horizontal advection, but by vertical processes that eventually overcome the freshening by southward advection and restore SSS to its premonsoon values. The salinity-stratified barrier layer hence only acts as a ''barrier'' for vertical heat fluxes, but is associated with intense vertical salt fluxes in the Bay of Bengal.

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‘Thermohaline front’ off the east coast of India and its generating mechanism

Cited by 19 publications

References 18 publications

Modulation of the Ganges‐Brahmaputra River Plume by the Indian Ocean Dipole and Eddies Inferred From Satellite Observations

Modulation of the Ganges‐Brahmaputra River Plume by the Indian Ocean Dipole and Eddies Inferred From Satellite Observations

A modeling study of processes controlling the Bay of Bengal sea surface salinity interannual variability

A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal

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