Space borne SAR observations of oceanic internal waves in North Bay of Bengal

Prasad, K. Venkatesh; Rajasekhar, M.

doi:10.1007/s11069-010-9630-6

Cited by 19 publications

(7 citation statements)

References 9 publications

(12 reference statements)

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“…Some of these studies reported that internal tides in this region are mainly generated at the shelf breaks and on the continental slopes (Rao et al, ). Surface manifestations of shoreward propagating short period internal waves in the western BoB, particularly in the northern part of the coast (18–19°N), were also reported based on Synthetic Aperture Radar (SAR) imageries (Joshi et al, ; Prasad & Rajasekhar, ). Some previous studies noted strong internal tide generation near the head Bay and temporal variability in internal tide activity due to changes in stratification (Pradhan et al, ; Rao et al, ).…”

Section: Introductionmentioning

confidence: 70%

Modeling of Internal Tides in the Western Bay of Bengal: Characteristics and Energetics

et al. 2019

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Generation and propagation of internal tides in the western Bay of Bengal (BoB) are investigated using observations from Acoustic Doppler Current Profilers and simulations from a very high resolution numerical ocean model. Observations show that semidiurnal internal tides in the southern and northern parts of the western BoB are more energetic during neap phase of the local barotropic tide than those during spring phase. Numerical simulations indicate that internal tides generated over the Andaman-Nicobar Ridge propagate westward for about 1,000-1,450 km across the BoB and finally impinge on the continental slopes off the east coast of India after 5-7 days. Energetic internal tides observed during the neap phase of the barotropic tides in the western BoB are mainly due to the arrival of remotely generated internal tides. We show that the variation in the onshore transmission of these remotely generated internal tides due to the topographic slope in the western BoB controls the strength of internal tide activity along the shelf. Superposition of reflected internal tides from continental slope, which are very steep in some regions and onshore propagating-waves generate partly standing waves. Numerical experiments suggest that internal tides coming from remote sources account for more than 80% of the total internal tide energy observed in the western BoB. Internal tide energy dissipation on the continental margins of the western BoB is about 3 to 4 times larger than the local generation, indicating that this region is a sink for remotely generated internal tide energy.

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Section: Introductionmentioning

confidence: 70%

Modeling of Internal Tides in the Western Bay of Bengal: Characteristics and Energetics

et al. 2019

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“…Although sole marks and the lower part of the classical tempestite beds can be easily explained with the unidirectional currents induced by breaking IWs (swash and backwash), the periclinalic dip orientation of laminae (bumped structure in the isotropic HCS) requires additional considerations. A relatively simple explanation would be to consider some interference such as reflection‐refraction between distinct trains of solitons or with sea‐bottom irregularities along the shelf such as canyons, banks, or islands (Prasad and Rajasekhar, 2011). Interference mechanism, or secondary internal waves (Vlasenko and Alpers, 2005) created by IWs approaching an obstacle on the sea floor, may also easily explain the tridimensional shape of isotropic HCS.…”

Section: Discussionmentioning

confidence: 99%

Internal waves vs. surface storm waves: a review on the origin of hummocky cross‐stratification

Morsilli

Pomar

2012

Terra Nova

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Terra Nova, 24, 273–282, 2012 Abstract Hummocky cross‐stratification (HCS) is considered a diagnostic structure of surface storm activity at the shoreface–offshore transition. However, the origin of HCS is still debated. Laboratory experiments have not yet reproduced it and direct observations on the continental shelves do not exist. Most hydrodynamic interpretations invoke pure oscillatory flows, unidirectional‐dominated combined flows and oscillatory‐dominated flows, but they all share the assumption of HCS to reflect the combined action of surface storm waves and related currents. Within this context of uncertainties, internal waves (gravity waves propagating along the pycnocline) provide an alternative mechanism to explain the origin of HCS. Internal waves breaking on the shelf create episodic high‐turbulence events and induce upslope‐ and downslope currents as well as oscillatory flows at the depth where the pycnocline intersects the sea floor. In this scenario, both the oscillatory‐ and the unidirectional components needed for HCS to form are not necessarily linked to surface storm waves, but can occur at various depth as far and near there is a pycnocline where internal waves can form.

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“…In the sharp density interface ( z = 29 m), the energy of zonal fluctuations averaged over a high‐frequency band (periods from ∼2 h to 9 min) is more than twice the energy of meridional fluctuations; the difference quickly ceased with depth, becoming 1 at z = 75 m, generally following the decrease of the total energy

true〈 e_{h f} true〉 true(z true)

shown in the left panel of Figure . Below 75 m, the ratio

true〈 S_{u} / S_{v} true〉

drops to 0.8 at z = 101 m, increasing then above 1.5 at z = 125 m. The

true〈 S_{u} / S_{v} true〉

ratio and quasiperiodic modulation of the internal wave energy suggest that the generation of high‐frequency oscillations in the upper part of the pycnocline may be linked to predominant zonal propagation of internal tide originated near the Andaman Islands [ Wijeratne et al ., ] or at the steep Sri Lankan continental slope [ Prasad and Rajasekhar , ] where the barotropic tides interact with bathymetry.…”

Section: Internal Wavesmentioning

confidence: 99%

“…Although satellite imagery shows the propagation of NLIW across the BoB toward Sri Lanka and their thronging along the continental shelf of India [ Jackson , ], NLIW to the west of Andaman and Nicobar Islands remains largely unexplored. Recently, NLIW observations from SAR images have been reported in the northern BoB [ Rao et al ., ; Prasad and Rajasekhar , ]. These waves propagated toward the Indian coast with wavelengths ∼600–700 m. On the Indian shelf of the northern BoB, semidiurnal tidal internal waves were characterized by amplitudes of ∼7 m, the amplitude of the diurnal internal tide being about half of it [ Sridevi et al ., ].…”

Section: Introductionmentioning

confidence: 99%

A snapshot of internal waves and hydrodynamic instabilities in the southern Bay of Bengal

et al. 2016

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Measurements conducted in the southern Bay of Bengal (BoB) as a part of the ASIRI‐EBoB Program portray the characteristics of high‐frequency internal waves in the upper pycnocline as well as the velocity structure with episodic events of shear instability. A 20 h time series of CTD, ADCP, and acoustic backscatter profiles down to 150 m as well as temporal CTD measurements in the pycnocline at z = 54 m were taken to the east of Sri Lanka. Internal waves of periods ∼10–40 min were recorded at all depths below a shallow (∼20–30 m) surface mixed layer in the background of an 8 m amplitude internal tide. The absolute values of vertical displacements associated with high‐frequency waves followed the Nakagami distribution with a median value of 2.1 m and a 95% quintile 6.5 m. The internal wave amplitudes are normally distributed. The tails of the distribution deviate from normality due to episodic high‐amplitude displacements. The sporadic appearance of internal waves with amplitudes exceeding ∼5 m usually coincided with patches of low Richardson numbers, pointing to local shear instability as a possible mechanism of internal‐wave‐induced turbulence. The probability of shear instability in the summer BoB pycnocline based on an exponential distribution of the inverse Richardson number, however, appears to be relatively low, not exceeding 4% for Ri < 0.25 and about 10% for Ri < 0.36 (K‐H billows). The probability of the generation of asymmetric breaking internal waves and Holmboe instabilities is above ∼25%.

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Space borne SAR observations of oceanic internal waves in North Bay of Bengal

Cited by 19 publications

References 9 publications

Modeling of Internal Tides in the Western Bay of Bengal: Characteristics and Energetics

Modeling of Internal Tides in the Western Bay of Bengal: Characteristics and Energetics

Internal waves vs. surface storm waves: a review on the origin of hummocky cross‐stratification

A snapshot of internal waves and hydrodynamic instabilities in the southern Bay of Bengal

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