Adrift Upon a Salinity-Stratified Sea: A View of Upper-Ocean Processes in the Bay of Bengal During the Southwest Monsoon

Lucas, Andrew J.; Nash, Jonathan D.; Pinkel, Robert; MacKinnon, Jennifer A.; Tandon, Amit; Mahadevan, Amala; Omand, Melissa M.; Freilich, Mara; Sengupta, Debasis; Ravichandran, M.; Boyer, Arnaud Le

doi:10.5670/oceanog.2016.46

Cited by 48 publications

(37 citation statements)

References 34 publications

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“…One such question is what suppresses diurnal wind variability in the northeast side of the bay (Figures b and ); the Doppler‐shifting mechanism proposed by Li and Carbone () was shown here to be incapable of suppressing diurnal variability in the northeast side of the bay. Another question is what role does diurnal ocean variability (Lucas et al, ; Shroyer et al, ) play in the western bay, where mixed layers are shallow (Lucas et al, ; Shroyer et al, ). Further wind observations and process studies hold promise to improve the representation of this important atmosphere‐ocean‐land surface interaction in climate models.…”

Section: Discussionmentioning

confidence: 99%

Diurnal Convection‐Wind Coupling in the Bay of Bengal

2017

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Satellite observations of infrared brightness temperature and rainfall have shown offshore propagation of diurnal rainfall signals in some coastal areas of the tropics, suggesting that diurnal rainfall is coupled to land‐sea breeze circulations. Here we utilize satellite observations of surface winds and rainfall to show the offshore copropagation of land breeze and diurnal rainfall signals for 300–400 km from the east coast of India into the Bay of Bengal. The wind observations are from the 2003 Quick Scatterometer (QuikSCAT)‐SeaWinds “tandem mission” and from 17 years of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI); the rainfall observations are from the TRMM 3B42 product and from TMI. The surface wind convergence maximum leads the rainfall maximum by 1–2 h in the western part of the bay, implying that the land breeze forces the diurnal cycle of rainfall. The phase speed of the offshore propagation is approximately 18 m s−1, consistent with a deep hydrostatic gravity wave forced by diurnal heating over India. Comparisons with a cloud system‐resolving atmospheric model and the ERA‐Interim reanalysis indicate that the models realistically simulate the surface land breeze but greatly underestimate the amplitude of the rainfall diurnal cycle. The satellite observations presented in this study therefore provide a benchmark for model representation of this important atmosphere‐ocean‐land surface interaction.

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Section: Discussionmentioning

confidence: 99%

Diurnal Convection‐Wind Coupling in the Bay of Bengal

2017

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“…An analysis of observed intraseasonal variability of salinity at the 15°N Research Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction (RAMA) mooring in the BoB also indicates that the variability is mainly due to lateral advection (Rao et al, ). Apart from lateral advection, vertical advection and mixing could also influence subseasonal salinity variability, although this subject began to receive attention only recently (Jinadasa et al, ; Lucas et al, ; Shroyer et al, ). The depth of the low‐salinity layer in the north BoB away from the western boundary is generally less than 30 m in June and July; the depth shallows to 5–15 m in August–September, once water from the GBM River arrives in the interior.…”

Section: Introductionmentioning

confidence: 99%

Subseasonal Dispersal of Freshwater in the Northern Bay of Bengal in the 2013 Summer Monsoon Season

et al. 2018

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Near-surface salinity in the north Bay of Bengal (BoB) is very low for nearly three seasons (July-January), due to freshwater input from summer monsoon rainfall and seasonal discharge from several major rivers, including the Ganga-Brahmaputra-Meghna and the Irrawady. The low-salinity surface layer leads to a very shallow density mixed layer, profoundly influencing air-sea interaction on diurnal to seasonal time scales. We use mooring and satellite observations to study the mechanisms responsible for lateral dispersal of river water in the north BoB on subseasonal time scales (days to weeks) during the summer monsoon season of 2013. A new ocean current data set, the BoB near-surface current and advection estimation (BoBcat), is developed to account for the influence of near-surface stratification on directly wind-forced currents. A salt balance based on Aquarius sea surface salinity, BoBcat currents and moored observations shows that subseasonal sea surface salinity variability is mainly due to lateral advection. A shallow Ekman current, forced by enhanced wind stress during an active spell of the monsoon in mid-August, plays a dominant role in moving freshwater from the western boundary to the interior. During subseasonal spells of weak monsoon winds, stirring by mesoscale eddies is the main mechanism of dispersal of low-salinity water. The dispersal of river water in the BoB is very sensitive to surface wind stress. SREE LEKHA ET AL. 6330

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“…A freely drifting ocean wave-powered Wirewalker profiler (Pinkel et al, 2011;Lucas et al, 2016) was deployed during survey A off the east coast and profiled as it drifted rapidly westward. The Wirewalker was equipped with GPS in the surface buoy, an RBR Concerto CTD, and a Nortek Signature 1 MHz Aquadopp current meter.…”

Section: Surveysmentioning

confidence: 99%