Investigating the role of air-sea forcing on the variability of hydrography, circulation, and mixed layer depth in the Arabian Sea and Bay of Bengal

Abstract. The seasonal variation of thermal, haline, net surface buoyancy flux, the Monin-Obukhov length (M-O length, L) and stability parameter, i.e. the ratio of M-O length to mixed layer depth (h) were studied in the Bay of Bengal (BoB) and the Arabian Sea (AS) for the years 2003 and 2004 using Argo temperature and salinity profiles. The relative quantitative influence of winds to surface buoyancy and the applicability of scaling mixed layer using M-O length in BoB and AS was brought out. Rotation and light penetration modify the mixed layer depth from M-O length during shoaling in spring giving L/h<1.

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

Meteorological Applications ◽

10.1002/met.1862 ◽

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

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

Journal of Climate ◽

10.1175/2008jcli2305.1 ◽

2008 ◽

Vol 21 (20) ◽

pp. 5254-5270 ◽

Cited By ~ 29

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.

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Phytoplankton bloom phenomena in the North Atlantic Ocean and Arabian Sea

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu241 ◽

2015 ◽

Vol 72 (6) ◽

pp. 2021-2028 ◽

Cited By ~ 5

Author(s):

John F. Marra ◽

Tommy D. Dickey ◽

Albert J. Plueddemann ◽

Robert A. Weller ◽

Christopher S. Kinkade ◽

...

Keyword(s):

Water Column ◽

Mixed Layer ◽

Arabian Sea ◽

Phytoplankton Bloom ◽

Mixed Layer Depth ◽

Ocean Dynamics ◽

Layer Depth ◽

Diurnal Variability ◽

Water Column Stratification ◽

Iceland Basin

Abstract We review bio-optical and physical data from three mooring experiments, the Marine Light–Mixed Layers programme in spring 1989 and 1991 in the Iceland Basin (59°N/21°W), and the Forced Upper Ocean Dynamics Experiment in the central Arabian Sea from October 1994 to 1995 (15.5°N/61.5°E). In the Iceland Basin, from mid-April to mid-June in 1989, chlorophyll-a concentrations are sensitive to small changes in stratification, with intermittent increases early in the record. The spring increase occurs after 20 May, coincident with persistent water column stratification. In 1991, the bloom occurs 2 weeks earlier than in 1989, with a background of strong short-term and diurnal variability in mixed layer depth and minimal horizontal advection. In the Arabian Sea, the mixing response to the northeast and southwest monsoons, plus the response to mesoscale eddies, produces four blooms over the annual cycle. The mixed layer depth in the Arabian Sea never exceeds the euphotic zone, allowing interactions between phytoplankton and grazer populations to become important. For all three mooring experiments, change in water column stratification is key in producing phytoplankton blooms.

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

Biogeosciences Discussions ◽

10.5194/bgd-10-16405-2013 ◽

2013 ◽

Vol 10 (10) ◽

pp. 16405-16452 ◽

Cited By ~ 1

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.

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