Estimates of Internal Tide Energetics in the Western Bay of Bengal

Mohanty, Sachiko; Rao, A. D.; Pradhan, Himansu Kesari

doi:10.1109/joe.2017.2765978

Cited by 5 publications

(5 citation statements)

References 30 publications

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“…It can be seen that internal tides are also generated off the coast of Myanmar, but the energy conversion rate is very less compared to other generation sites of the Andaman Sea. Here it is found that the maximum conversion rate is about 8 W/m 2 in the Andaman Sea that is very high compared to that of over the Western BoB, where the conversion rate is about 1 W/m 2 (Mohanty et al, ). The domain‐integrated barotropic‐to‐baroclinic semidiurnal energy conversion rate is about 23 GW, which corresponds to about 3% of the global conversion rate estimated by Niwa and Hibiya () and about 1% of the power required to maintain the global thermohaline circulation (Munk & Wunsch, ).…”

Section: Resultsmentioning

confidence: 86%

Energetics of Semidiurnal Internal Tides in the Andaman Sea

2018

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A detailed energetic estimate of the barotropic and baroclinic semidiurnal internal tides over the Andaman Sea is performed by using the three-dimensional Massachusetts Institute of Technology general circulation model. Model-simulated currents and density fields are validated using in situ observations with high temporal resolution from a buoy located at 10.5°N, 94°E. The generation and dissipation regions of internal tides and their propagation in the domain are identified by quantifying the distribution of total tidal energy among generation, radiation, and dissipation. The model simulation suggests that the internal tides are mainly generated in the north of Sumatra coast, in the Sombrero channel, south of the Car Nicobar Island, and north of the Andaman Island. From these generation sites, a portion of the energy propagates into the Andaman Sea and the remainder propagates toward the southern Bay of Bengal. The depth-integrated baroclinic energy fluxes are found to be a maximum of~30 kW/m at the major generation sites in the domain. The model-estimated energy dissipation rates suggest that the maximum amount of energy dissipates near the generation sites themselves. In the region north of the Sumatra coast, almost 87% of the barotropic energy is converted into baroclinic energy and 23% (0.91 GW) of the converted baroclinic energy is ultimately radiated out from the generation sites. The barotropic-to-baroclinic conversion rate over the whole domain is estimated to be~23 GW, out of which, a major part~18 GW (80%) dissipates near the generation sites. This reveals that the local dissipation of baroclinic energy dominates in the Andaman Sea.Plain Language Summary Internal waves (IWs) in the oceans are ubiquitous phenomena, and they play an important role for a wide range of oceanic processes such as transfer of energy and momentum in the interior of global oceans, sound wave propagation, vertical transport of nutrients, and regional ecosystems. Andaman Sea is known to be an active region in the world's ocean where IWs of exceptionally high amplitudes are observed, but it still remains as one of the least explored regions. In this present study, spatial distribution of generation, propagation, and dissipation of IWs of tidal frequency, that is, internal tides are examined using a numerical model. The detailed energy budget analysis is carried out for this region. The simulated results show that, from the total barotropic-to-baroclinic conversion rate, 80% (~18 GW) of internal tide energy dissipates near the generation sites in the Andaman Sea.

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Section: Resultsmentioning

confidence: 86%

Energetics of Semidiurnal Internal Tides in the Andaman Sea

2018

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“…Between 10 and 80 km, the GM continuum levels are well below the measurements, and other processes must be at play. Given their abundance, it is likely that near-inertial oscillations (Johnston et al 2016) and internal tides (Murty and Henry 1983;Mohanty et al 2018), neither of which is well represented by the GM spectrum, may account for a fair portion of the divergent component in the Bay. Indeed, there are locations in the Bay where the tidal displacement signal is larger than the inertia-gravity GM spectrum (Wijesekera et al 2016).…”

Section: A Spectramentioning

confidence: 99%

Near-Surface Ocean Kinetic Energy Spectra and Small-Scale Intermittency from Ship-Based ADCP Data in the Bay of Bengal

Sukhatme

Chaudhuri

MacKinnon

et al. 2020

Journal of Physical Oceanography

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Abstract Horizontal currents in the Bay of Bengal were measured on eight cruises covering a total of 8600 km using a 300-kHz acoustic Doppler current profiler (ADCP). The cruises are distributed over multiple seasons and regions of the Bay. Horizontal wavenumber spectra of these currents over depths of 12–54 m and wavelengths from 2 to 400 km were decomposed into rotational and divergent components assuming isotropy. An average of across- and along-track spectra over all cruises shows that the spectral slope of horizontal kinetic energy for wavelengths of 10–80-km scales with an exponent of −1.7 ± 0.05, which transitions to a steeper slope for wavelengths above 80 km. The rotational component is significantly larger than the divergent component at scales greater than 80 km, while the ratio of the two is nearly constant with a mean of 1.16 ± 0.4 between 10 and 80 km. The measurements show a fair amount of variability and spectral levels vary between cruises by about a factor of 5 over 10–100 km. Velocity differences over 10–80 km show probability density functions and structure functions with stretched exponential behavior and anomalous scaling. Comparisons with the Garrett–Munk internal wave spectrum indicate that inertia–gravity waves account for only a modest fraction of the kinetic energy between 10 and 80 km. These constraints suggest that the near-surface flow in the Bay is primarily balanced and follows a forward enstrophy transfer quasigeostrophic regime for wavelengths greater than approximately 80 km, with a larger role for unbalanced rotating stratified turbulence and internal waves at smaller scales.

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“…Earlier studies on semidiurnal internal tides in the western BoB were mainly based on short records (a few days) of currents and temperature as well as simulations using numerical models (Joshi et al, ; Mohanty et al, ; Pradhan et al, ; Pradhan et al, ; Rao et al, ; Rao et al, ). 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, ).…”

Section: Introductionmentioning

confidence: 99%

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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Estimates of Internal Tide Energetics in the Western Bay of Bengal

Cited by 5 publications

References 30 publications

Energetics of Semidiurnal Internal Tides in the Andaman Sea

Energetics of Semidiurnal Internal Tides in the Andaman Sea

Near-Surface Ocean Kinetic Energy Spectra and Small-Scale Intermittency from Ship-Based ADCP Data in the Bay of Bengal

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

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