Observations of barrier layer formation in the Bay of Bengal during summer monsoon

Vinayachandran, P. N.; Murty, V. S. N.; Babu, V. Ramesh

doi:10.1029/2001jc000831

Cited by 313 publications

(241 citation statements)

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“…High SST in the BoB is conducive to deep convection in the atmosphere and hence precipitation during the SW monsoon season (Gadgil et al 1984;Shenoi et al 2002). Altered atmospheric convection results in variations in air-sea heat flux, which can further influence the convection itself via SST changes (Krishnamurti et al 1988).…”

Section: Introductionmentioning

confidence: 99%

“…The unique summertime and wintertime oceanic conditions associated with the presence of a low-salinity layer lead to marked variations in density stratification and vertical mixing in the BoB both in summer (Vinayachandran et al 2002) and winter (Shetye et al 1996). The strong halocline associated with the surface freshwater cap shoals the density mixed layer (ML), while the isothermal layer depth (ILD) is usually deeper.…”

Section: Introductionmentioning

confidence: 99%

“…That is, the stratified BL retains atmospheric heat and momentum inputs predominantly within the ML while reducing the entrainment of the cooler thermocline water from the bottom (Vialard and Delecluse 1998). A survey of BL thickness (BLT) by Sprintall and Tomczak (1992) using the Levitus (1982) climatology indicates that BLs exist throughout the year in the BoB, with a thickness of 25 m during August-October in the northwestern part of the bay (Vinayachandran et al 2002). Rao and Sivakumar (2003) also discuss the formation mechanism and seasonal cycle of the BL in the northern Indian Ocean.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal Effects of Indian Ocean Freshwater Forcing in a Regional Coupled Model*

et al. 2009

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Effects of freshwater forcing from river discharge into the Indian Ocean on oceanic vertical structure and the Indian monsoons are investigated using a fully coupled, high-resolution, regional climate model. The effect of river discharge is included in the model by restoring sea surface salinity (SSS) toward observations. The simulations with and without this effect in the coupled model reveal a highly seasonal influence of salinity and the barrier layer (BL) on oceanic vertical density stratification, which is in turn linked to changes in sea surface temperature (SST), surface winds, and precipitation.During both boreal summer and winter, SSS relaxation leads to a more realistic spatial distribution of salinity and the BL in the model. In summer, the BL in the Bay of Bengal enhances the upper-ocean stratification and increases the SST near the river mouths where the freshwater forcing is largest. However, the warming is limited to the coastal ocean and the amplitude is not large enough to give a significant impact on monsoon rainfall.The strengthened BL during boreal winter leads to a shallower mixed layer. Atmospheric heat flux forcing acting on a thin mixed layer results in an extensive reduction of SST over the northern Indian Ocean. Relatively suppressed mixing below the mixed layer warms the subsurface layer, leading to a temperature inversion. The cooling of the sea surface induces a large-scale adjustment in the winter atmosphere with amplified northeasterly winds. This impedes atmospheric convection north of the equator while facilitating it in the austral summer intertropical convergence zone, resulting in a hemispheric-asymmetric response pattern. Overall, the results suggest that freshwater forcing from the river discharges plays an important role during the boreal winter by affecting SST and the coupled ocean-atmosphere interaction, with potential impacts on the broadscale regional climate.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Seasonal Effects of Indian Ocean Freshwater Forcing in a Regional Coupled Model*

et al. 2009

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“…The presence of fresh water leads to salt-stratified upper-ocean water column and the formation of a barrier layer (BL), a layer sandwiched between the bottom of the mixed layer (ML) and the top of the thermocline, in the BoB (Lukas and Lindstrom, 1991;Vinayachandran et al, 2002;Thadathil et al, 2007). The BL restricts the entrainment of colder waters from thermocline region into the mixed layer; it thereby maintains a warmer ML and sea surface temperature (SST).…”

Section: Introductionmentioning

confidence: 99%

Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere–ocean–wave model

2018

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Abstract. A coupled atmosphere-ocean-wave model was used to examine mixing in the upper-oceanic layers under the influence of a very severe cyclonic storm Phailin over the Bay of Bengal (BoB) during 10-14 October 2013. The coupled model was found to improve the sea surface temperature over the uncoupled model. Model simulations highlight the prominent role of cyclone-induced near-inertial oscillations in subsurface mixing up to the thermocline depth. The inertial mixing introduced by the cyclone played a central role in the deepening of the thermocline and mixed layer depth by 40 and 15 m, respectively. For the first time over the BoB, a detailed analysis of inertial oscillation kinetic energy generation, propagation, and dissipation was carried out using an atmosphere-ocean-wave coupled model during a cyclone. A quantitative estimate of kinetic energy in the oceanic water column, its propagation, and its dissipation mechanisms were explained using the coupled atmosphere-ocean-wave model. The large shear generated by the inertial oscillations was found to overcome the stratification and initiate mixing at the base of the mixed layer. Greater mixing was found at the depths where the eddy kinetic diffusivity was large. The baroclinic current, holding a larger fraction of kinetic energy than the barotropic current, weakened rapidly after the passage of the cyclone. The shear induced by inertial oscillations was found to decrease rapidly with increasing depth below the thermocline. The dampening of the mixing process below the thermocline was explained through the enhanced dissipation rate of turbulent kinetic energy upon approaching the thermocline layer. The wave-current interaction and nonlinear wave-wave interaction were found to affect the process of downward mixing and cause the dissipation of inertial oscillations.

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“…Two cells of very low density are found off the central east coast of India and northwest of the Andaman Islands, where freshwater discharges from the Krishna and Irrawady Rivers, respectively, enter the Bay [4] . Work has already been done on the entire oceans on geostrophic current using altimetry data and in the Indian Ocean [5][6][7][8] . During the 2004 tsunami, research on a satellite view of internal wave [9] found the effect of tsunami on marine ecosystem [1] .…”

Section: Densitymentioning

confidence: 99%

Effect of the 2004 â€˜Boxing Dayâ€™ Tsunami on Water Properties and Currents in the Bay of Bengal

Reddy¹,

Aung²,

Singh³

2009

American J. of Environmental Sciences

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Problem statement: Variation of temperature, salinity and geostrophic current in the Bay of Bengal due to the 2004 Boxing Day tsunami was investigated in this project using ARGO float and absolute dynamic height topography data. This was done to determine the effect of the tsunami on the water properties in the bay. Approach: The study area was between latitudes 5º N and 25º N and longitudes 75º E and 100º E. Data from November 2004 and January 2005 were analyzed. The drift velocity of the ARGO float (within the study area) at its parking depth was calculated and compared with the geostrophic current at this depth in order to determine the appropriate reference level (level of no motion) for the study area. Results: The geostrophic current, using the Helland-Hansen equation, requires a reference level, which was then used to calculate the surface geostrophic current using the absolute dynamic height obtained from satellite altimetry. The appropriate level of no motion in the Bay of Bengal region was found to be 1500 m. As a result of the tsunami, the variation in sea surface temperature was around 2-3ºC and the variation in salinity was around 2-3 psu in the region. Accordingly, the dynamic height increased to about 20-30 dym cm just after the tsunami and abruptly changed the geostrophic surface currents pattern in Bay of Bengal. A few days after the tsunami, the geostrophic surface currents returned to normal. Conclusions: The variation of temperature and salinity in the Bay are the major causes of changes in the dynamic height, which results in the variation of geostrophic currents.

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Observations of barrier layer formation in the Bay of Bengal during summer monsoon

Cited by 313 publications

References 22 publications

Seasonal Effects of Indian Ocean Freshwater Forcing in a Regional Coupled Model*

Seasonal Effects of Indian Ocean Freshwater Forcing in a Regional Coupled Model*

Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere–ocean–wave model

Effect of the 2004 â€˜Boxing Dayâ€™ Tsunami on Water Properties and Currents in the Bay of Bengal

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