Estimation of Vertical Heat Diffusivity at the Base of the Mixed Layer in the Bay of Bengal

2020 ◽  
Vol 125 (5) ◽  
Author(s):  
M. S. Girishkumar ◽  
K. Ashin ◽  
M. J. McPhaden ◽  
B. Balaji ◽  
B. Praveenkumar
Keyword(s):  
Mixed Layer ◽  
Bay Of Bengal ◽  
Heat Diffusivity ◽  
Vertical Heat

scholarly journals On the Nature of Near-Inertial Oscillations in the Uppermost Part of the Ocean and a Possible Route toward HF Radar Probing of Stratification

2015 ◽  
Vol 45 (10) ◽  
pp. 2660-2678 ◽  
Author(s):  
Victor I. Shrira ◽  
Philippe Forget
Keyword(s):  
Mixed Layer ◽  
Vertical Mixing ◽  
Hf Radar ◽  
Momentum Exchange ◽  
Inertial Oscillations ◽  
Weak Density ◽  
Gulf Of Lion ◽  
Vertical Heat ◽  
Northwestern Mediterranean ◽  
Vertical Localization

AbstractInertial band response of the upper ocean to changing wind is studied both theoretically and by analysis of observations in the northwestern Mediterranean. On the nontraditional f plane, because of the horizontal component of the earth’s rotation for waves of inertial band with frequencies slightly below the local inertial frequency f, there is a waveguide in the mixed layer confined from below by the pycnocline. It is argued that when the stratification is shallow these waves are most easily and strongly excited by varying winds as near-inertial oscillations (NIOs). These motions have been overlooked in previous studies because they are absent under the traditional approximation. The observations that employed buoys with thermistors, ADCPs, and two 16.3-MHz Wellen Radar (WERA) HF radars were carried out in the Gulf of Lion in April–June 2006. The observations support the theoretical picture: a pronounced inertial band response occurs only in the presence of shallow stratification and is confined to the mixed layer, and the NIO penetration below the stratified layer is weak. NIO surface magnitude and vertical localization are strongly affected by the presence of even weak density stratification in the upper 10 m. The NIO surface signatures are easily captured by HF radars. Continuous 1.8-yr HF observations near the Porquerolles Island confirm that shallow stratification is indeed the precondition for a strong NIO response. The response sensitivity to stratification provides a foundation for developing HF radar probing of stratification and, indirectly, vertical mixing, including spotting dramatic mixing events and spikes of vertical heat, mass, and momentum exchange.

scholarly journals Impact of ocean mixed‐layer depth initialization on the simulation of tropical cyclones over the Bay of Bengal using the WRF‐ARW model

2019 ◽  
Vol 27 (1) ◽  
Author(s):  
Viswanadhapalli Yesubabu ◽  
Vijaya Kumari Kattamanchi ◽  
Naresh Krishna Vissa ◽  
Hari Prasad Dasari ◽  
Vijaya Bhaskara Rao Sarangam
Keyword(s):  
Tropical Cyclones ◽  
Mixed Layer ◽  
Bay Of Bengal ◽  
Mixed Layer Depth ◽  
Ocean Mixed Layer ◽  
Layer Depth ◽  
Arw Model ◽  
Ocean Mixed Layer Depth

scholarly journals Ocean–Atmosphere Coupling in the Monsoon Intraseasonal Oscillation: A Simple Model Study

2008 ◽  
Vol 21 (20) ◽  
pp. 5254-5270 ◽  
Author(s):  
Gilles Bellon ◽  
Adam H. Sobel ◽  
Jerome Vialard
Keyword(s):  
Mixed Layer ◽  
Bay Of Bengal ◽  
Mixed Layer Depth ◽  
Intraseasonal Oscillation ◽  
Thermal Inertia ◽  
Coupled Model ◽  
Boreal Winter ◽  
Quasi Equilibrium ◽  
Layer Depth ◽  
Ocean Atmosphere

Abstract A simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the effect of ocean–atmosphere coupling on the Asian monsoon intraseasonal oscillation. The model consists of a linear atmospheric model of intermediate complexity based on quasi-equilibrium theory coupled to a simple, linear model of the upper ocean. This model has one unstable eigenmode with a period in the 30–60-day range and a structure similar to the observed northward-propagating intraseasonal oscillation in the Bay of Bengal/west Pacific sector. The ocean–atmosphere coupling is shown to have little impact on either the growth rate or latitudinal structure of the atmospheric oscillation, but it reduces the oscillation’s period by a quarter. At latitudes corresponding to the north of the Indian Ocean, the sea surface temperature (SST) anomalies lead the precipitation anomalies by a quarter of a period, similarly to what has been observed in the Bay of Bengal. The mixed layer depth is in phase opposition to the SST: a monsoon break corresponds to both a warming and a shoaling of the mixed layer. This behavior results from the similarity between the patterns of the predominant processes: wind-induced surface heat flux and wind stirring. The instability of the seasonal monsoon flow is sensitive to the seasonal mixed layer depth: the oscillation is damped when the oceanic mixed layer is thin (about 10 m deep or thinner), as in previous experiments with several models aimed at addressing the boreal winter Madden–Julian oscillation. This suggests that the weak thermal inertia of land might explain the minima of intraseasonal variance observed over the Asian continent.

scholarly journals Vertical distribution of chlorophyll in dynamically distinct regions of the southern Bay of Bengal

2018 ◽  
Author(s):  
Venugopal Thushara ◽  
Puthenveettil Narayana Menon Vinayachandran ◽  
Adrian J. Matthews ◽  
Benjamin G. M. Webber ◽  
Bastien Y. Queste
Keyword(s):  
Sri Lanka ◽  
Vertical Distribution ◽  
Mixed Layer ◽  
Bay Of Bengal ◽  
Dominant Role ◽  
Chlorophyll Concentration ◽  
Ecosystem Model ◽  
Boreal Summer ◽  
South West Monsoon ◽  
The Vertical Distribution

Abstract. The Bay of Bengal (BoB) generally exhibits surface oligotrophy, due to nutrient limitation induced by strong salinity stratification. Nevertheless, there are hot spots of biological activity in the BoB where the monsoonal forcings are strong enough to break the stratification; one such region being the southern BoB, east of Sri Lanka. A recent field program conducted during the summer monsoon of 2016, as a part of the Bay of Bengal Boundary Layer Experiment (BoBBLE), provides a unique high-resolution dataset of the vertical distribution of chlorophyll in the southern BoB using ocean gliders along with shipboard CTD measurements. Observations were carried out for a duration of 12–20 days during a suppressed phase of the Boreal Summer Intraseasonal Oscillation (BSISO), along a longitudinal transect at 8° N, extending from 85.3–89° E, covering the dynamically active regions of the Sri Lanka Dome (SLD) and the South- west Monsoon Current (SMC). Mixing and upwelling induced by the monsoonal wind forcing enhanced chlorophyll concentrations (0.3–0.7 mg m−3) in the surface layers. Observations reveal the presence of prominent deep chlorophyll maxima (DCM; 0.3–1.2 mg m−3) at intermediate depths (20–50 m), generally below the mixed layer and above the thermocline, signifying the contribution of subsurface productivity on the biological carbon cycling in the BoB. The shape of chlorophyll profiles varied in different dynamical regimes indicating that the mechanisms determining the vertical distribution of chlorophyll are intricate; upwelling favoured sharp and intense DCM, whereas mixing resulted in diffuse and weaker DCM. Within the SLD, open ocean Ekman pumping and the doming of thermocline favoured a substantial increase in chlorophyll concentration. Farther east, the thermocline was deeper and moderate surface blooms were triggered by intermittent mixing events. Stabilising surface freshening events and barrier layer formation were often observed to inhibit the surface blooms. The pathway of SMC intrusion was marked by a distinct band of chlorophyll, indicating the advective effect of biologically rich Arabian Sea waters. The region of monsoon current exhibits the strongest DCM as well as the highest column-integrated chlorophyll. Observations suggest that the persistence of DCM in the southern BoB is promoted by surface oligotrophy, which reduces the self-shading effect of phytoplankton and shallow mixed layers, which prevent the vertical redistribution of subsurface phytoplankton. Results from a coupled physical-ecosystem model substantiate the dominant role of mixed layer processes associated with the monsoon in controlling the nutrient distribution and biological productivity in the southern BoB. The present study provides new insights into the vertical distribution of chlorophyll in the BoB, which is not captured in satellite mea- surements, emphasizing the need for extensive in situ sampling and ecosystem model-based efforts for a better understanding of the monsoonal bio-physical interactions and the potential climatic feedbacks.

scholarly journals Mixed layer variability and chlorophyll <i>a</i> biomass in the Bay of Bengal

2013 ◽  
Vol 10 (10) ◽  
pp. 16405-16452 ◽  
Author(s):  
J. Narvekar ◽  
S. Prasanna Kumar
Keyword(s):  
Mixed Layer ◽  
Bay Of Bengal ◽  
Mixed Layer Depth ◽  
Chlorophyll Concentration ◽  
Short Wave ◽  
Wave Radiation ◽  
Layer Depth ◽  
Short Wave Radiation ◽  
Deep Mixed Layer ◽  
Monsoon Winds

Abstract. Mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the chlorophyll concentration. In this paper we examined the seasonal variability of the mixed layer depth in the Bay of Bengal, the factors responsible for it and the coupling of mixed layer processes to the chlorophyll biomass using a suite of in situ as well as remote sensing data. The basin-wide mixed layer depth was the shallowest during spring intermonsoon, which was associated with strong themohaline stratification of the upper water column. The prevailing winds which were the weakest of all the seasons were unable to break the stratification leading to the observed shallow mixed layer. Consistent with the warm oligotrophic upper ocean, the surface chlorophyll concentrations were the least and the vertical profile of chlorophyll was characterized by a subsurface chlorophyll maximum. Similarly, during summer though the monsoon winds were the strongest they were unable to break the upper ocean haline-stratification in the northern Bay brought about by a combination of excess precipitation over evaporation and fresh water influx from rivers adjoining the Bay of Bengal. Consistent with this though the nitrate concentrations were high in the northern part of the Bay, the chlorophyll concentrations were low indicating the light limitation. In contrast, in the south, advection of high salinity waters from the Arabian Sea coupled with the westward propagating Rossby waves of annual periodicity were able to decrease stability of the upper water column and the prevailing monsoon winds were able to initiate deep mixing leading to the observed deep mixed layer. The high chlorophyll concentration observed in the south resulted from the positive wind stress curl which pumped nutrient rich subsurface waters to the euphotic zone. The southward extension of the shallow mixed layer in fall intermonsoon resulted from the advection of low salinity waters from the northern Bay combined with the secondary heating by the incoming short wave radiation. The satellite-derived chlorophyll pigment concentration during fall intermonsoon was similar to that of summer but with reduced values. The basin-wide deep mixed layer during winter resulted from a combination of reduced short wave radiation, increase in salinity and comparatively stronger winds. The mismatch between the low nitrate and comparatively higher chlorophyll biomass during winter indicated the efficacy of the limited nitrate data to adequately resolve the coupling between the mixed layer processes and the chlorophyll biomass.

scholarly journals The effect of seasonally and spatially varying chlorophyll on Bay of Bengal surface ocean properties and the South Asian Monsoon

2020 ◽  
Author(s):  
Jack Giddings ◽  
Adrian J. Matthews ◽  
Nicholas P. Klingaman ◽  
Karen J. Heywood ◽  
Manoj Joshi ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Mixed Layer ◽  
Bay Of Bengal ◽  
Optical Parameter ◽  
Southwest Monsoon ◽  
Northeast India ◽  
Radiative Heating ◽  
Radiation Absorption ◽  
Upper Ocean ◽  
Spatially Varying

Abstract. Chlorophyll absorbs solar radiation in the upper ocean, increasing mixed-layer radiative heating and sea surface temperatures (SST). The solar absorption caused by chlorophyll can be parameterised as an optical parameter, h2, the scale depth of absorption of blue light. Seasonally and spatially varying h2 in the Bay of Bengal was imposed in a coupled ocean-atmosphere model to investigate the effect of chlorophyll distributions on regional SST, atmospheric circulation and precipitation. There are both direct local upper-ocean effects, through changes in solar radiation absorption and indirect remote atmospheric responses. The depth of the mixed layer relative to the perturbed solar penetration depths modulates the response of SST to chlorophyll. The largest SST response to chlorophyll forcing occurs in coastal regions, where chlorophyll concentrations are high (> 1 mg m−3), and when climatological mixed layer depths shoal during the intermonsoon periods. Precipitation increases significantly by up to 3 mm day−1 across coastal Myanmar during the southwest monsoon onset and over northeast India and Bangladesh during the Autumn intermonsoon period, decreasing model biases.

Role of ocean dynamics in the evolution of mixed-layer temperature in the Bay of Bengal during the summer monsoon

2021 ◽  
pp. 101895
Author(s):  
Vineet Jain ◽  
D. Shankar ◽  
P.N. Vinayachandran ◽  
A. Mukherjee ◽  
P. Amol
Keyword(s):  
Summer Monsoon ◽  
Mixed Layer ◽  
Bay Of Bengal ◽  
Ocean Dynamics ◽  
Mixed Layer Temperature

scholarly journals Mixed Layer Temperature Budget for the Northward Propagating Summer Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal

2017 ◽  
Vol 122 (11) ◽  
pp. 8841-8854 ◽  
Author(s):  
M. S. Girishkumar ◽  
J. Joseph ◽  
V. P. Thangaprakash ◽  
V. Pottapinjara ◽  
M. J. McPhaden
Keyword(s):  
Summer Monsoon ◽  
Mixed Layer ◽  
Bay Of Bengal ◽  
Intraseasonal Oscillation ◽  
Mixed Layer Temperature
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