What Controls Seasonal Evolution of Sea Surface Temperature in the Bay of Bengal? Mixed Layer Heat Budget Analysis Using Moored Buoy Observations Along 90°E

Abstract Using results from the Simple Ocean Data Assimilation (SODA), this study assesses the mixed layer heat budget to identify the mechanisms that control the interannual variation of sea surface temperature (SST) off Java and Sumatra. The analysis indicates that during the positive Indian Ocean Dipole (IOD) years, cold SST anomalies are phase locked with the season cycle. They may exceed −3°C near the coast of Sumatra and extend as far westward as 80°E along the equator. The depth of the thermocline has a prominent influence on the generation and maintenance of SST anomalies. In the normal years, cooling by upwelling–entrainment is largely counterbalanced by warming due to horizontal advection. In the cooling episode of IOD events, coastal upwelling–entrainment is enhanced, and as a result of mixed layer shoaling, the barrier layer no longer exists, so that the effect of upwelling–entrainment can easily reach the surface mixed layer. Horizontal advection spreads the cold anomaly to the interior tropical Indian Ocean. Near the coast of Java, the northern branch of an anomalous anticyclonic circulation spreads the cold anomaly to the west near the equator. Both the anomalous advection and the enhanced, wind-driven upwelling generate the cold SST anomaly of the positive IOD. At the end of the cooling episode, the enhanced surface thermal forcing overbalances the cooling effect by upwelling/entrainment, and leads to a warming in SST off Java and Sumatra.

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Seasonality of Decadal Sea Surface Temperature Anomalies in the Northwestern Pacific

Journal of Climate ◽

10.1175/jcli3807.1 ◽

2006 ◽

Vol 19 (12) ◽

pp. 2953-2968 ◽

Cited By ~ 7

Author(s):

Takashi Mochizuki ◽

Hideji Kida

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

Surface Heat Flux ◽

Heat Budget ◽

Surface Heat ◽

Sea Surface ◽

Northwestern Pacific ◽

Sst Anomaly

Abstract The seasonality of the decadal sea surface temperature (SST) anomalies and the related physical processes in the northwestern Pacific were investigated using a three-dimensional bulk mixed layer model. In the Kuroshio–Oyashio Extension (KOE) region, the strongest decadal SST anomaly was observed during December–February, while that of the central North Pacific occurred during February–April. From an examination of the seasonal heat budget of the ocean mixed layer, it was revealed that the seasonal-scale enhancement of the decadal SST anomaly in the KOE region was controlled by horizontal Ekman temperature transport in early winter and by vertical entrainment in autumn. The temperature transport by the geostrophic current made only a slight contribution to the seasonal variation of the decadal SST anomaly, despite controlling the upper-ocean thermal conditions on decadal time scales through the slow Rossby wave adjustment to the wind stress curl. When averaging over the entire KOE region, the contribution from the net sea surface heat flux was also no longer significantly detected. By examining the horizontal distributions of the local thermal damping rate, however, it was concluded that the wintertime decadal SST anomaly in the eastern KOE region was rather damped by the net sea surface heat flux. It was due to the fact that the anomalous local thermal damping of the SST anomaly resulting from the vertical entrainment in autumn was considerably strong enough to suppress the anomalous local atmospheric thermal forcing that acted to enhance the decadal SST anomaly.

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Seasonal and inter-annual variability of the sea surface temperature and mixed layer depth in the southern Bay of Bengal

Advances in Oceanography and Limnology ◽

10.4081/aiol.2013.5337 ◽

2013 ◽

Vol 4 (1) ◽

pp. 70

Author(s):

R. Ranith ◽

L. Senthilnathan ◽

M. Machendiranathan ◽

T. Thangaradjou ◽

A. Saravanakumar

Keyword(s):

Wind Speed ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

Bay Of Bengal ◽

Mixed Layer Depth ◽

Sea Surface ◽

Climate Change Scenarios ◽

Layer Depth ◽

South West Monsoon

Argo float data supplemented with satellite measurements was used to study the seasonal and inter-annual variation in wind speed, sea surface temperature (SST) and mixed layer depth (MLD) of the southern Bay of Bengal from 2003 through 2010. Due to persistence of wind, clear sky and high insolation an increase in SST by about 2°C is evident during summer months (March-May) and is followed by shallowed MLD with a minimum depth of 9.3 m during summer 2004. MLD reached the maximum depth during monsoon season (November-December) and often extends to post monsoon (February) owing to strong monsoon wind, cloudy sky and SST plummeted by 3°C. During the inter-monsoon period (August-October) the MLD shallowed and maintained a depth of 20–30 m all through the study period. High wind accompanied with moderate temperature (SST) due to the south west monsoon leads to decreased MLD with an average depth of 44 m in July. Analysis of wind speed, SST and MLD suggested that out of various meteorological parameters wind speed and induced mixing are highly influential in MLD formation. Reduced occurrence and amplitude of MLD deepening noticed in recent years can be attributed to the evident climate change scenarios. Large scale upper ocean variability observed from the present study has innumerable antagonistic consequences on the marine ecosystem which is evident from various events of seagrass burns and coral bleaching which have occurred in the last decade.

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A numerical study on the mixed layer depth variability and its influence on the sea surface temperature during 2013–2014 in the Bay of Bengal and Equatorial Indian Ocean

Ocean Dynamics ◽

10.1007/s10236-021-01452-1 ◽

2021 ◽

Author(s):

Radharani Sen ◽

Pavanathara Augustine Francis ◽

Arun Chakraborty ◽

John B. Effy

Keyword(s):

Indian Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

Bay Of Bengal ◽

Numerical Study ◽

Mixed Layer Depth ◽

Equatorial Indian Ocean ◽

Sea Surface ◽

Layer Depth

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Air–Sea Interactions among Oceanic Low-Level Cloud, Sea Surface Temperature, and Atmospheric Circulation on an Intraseasonal Time Scale in the Summertime North Pacific Based on Satellite Data Analysis

Journal of Climate ◽

10.1175/jcli-d-19-0670.1 ◽

2020 ◽

Vol 33 (21) ◽

pp. 9195-9212

Author(s):

Naoya Takahashi ◽

Tadahiro Hayasaka

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

North Pacific ◽

Time Scale ◽

Heat Budget ◽

Sea Surface ◽

Shallow Convection ◽

Low Level ◽

Budget Analysis ◽

Interaction Processes

AbstractLow-level cloud plays a key role in modulating air–sea interaction processes and sea surface temperature (SST) variability. The present study investigated the evolution process of oceanic low-level cloud cover (LCC) and related air–sea interaction processes on an intraseasonal time scale in the summertime (June–October) North Pacific (30°–40°N, 165°–175°E) based on satellite observational and reanalysis datasets from 2003 to 2016. The intraseasonal time scale (20–100 days) is dominant not only for the LCC, but also for LCC controlling factors, that is, SST, estimated inversion strength (EIS), and horizontal temperature advection (Tadv). To reveal the lead–lag relationship among these variables, we conducted phase composite analysis with a bandpass filter based on the intraseasonal variability (ISV) of LCC. It suggests that ISV of LCC leads to that of SST and that horizontal dry–cold advection from the poleward region leads to increasing LCC and decreasing SST. The increasing LCC corresponds to a positive relative humidity (RH) anomaly in the lower troposphere, which is due to adiabatic cooling with shallow convection, vertical moisture advection, and meridional RH advection associated with the anomalous cold Tadv. Heat budget analysis of the ocean mixed layer suggests the importance of anomalous dry–cold advection for cooling SST, not only via enhanced latent heat release but also via decreased downward shortwave radiation at the sea surface according to cloud radiative effect with a positive LCC anomaly. Determining the detailed lead–lag relationship between LCC and its controlling factor is a good approach to understand mechanisms of the local processes of both low-level cloud evolution and air–sea interaction.

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Seasonal and inter-annual variability of the sea surface temperature and mixed layer depth in the southern Bay of Bengal

Advances in Oceanography and Limnology ◽

10.1080/19475721.2013.793741 ◽

2013 ◽

Vol 4 (1) ◽

pp. 70-81

Author(s):

R. Ranith ◽

L. Senthilnathan ◽

M. Machendiranathan ◽

T. Thangaradjou ◽

A. Saravanakumar

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

Bay Of Bengal ◽

Mixed Layer Depth ◽

Sea Surface ◽

Layer Depth ◽

Annual Variability

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Spatial and temporal variability of solar penetration depths in the Bay of Bengal and its impact on sea surface temperature (SST) during the summer monsoon

Ocean Science ◽

10.5194/os-17-871-2021 ◽

2021 ◽

Vol 17 (4) ◽

pp. 871-890

Author(s):

Jack Giddings ◽

Karen J. Heywood ◽

Adrian J. Matthews ◽

Manoj M. Joshi ◽

Benjamin G. M. Webber ◽

...

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

Bay Of Bengal ◽

Southwest Monsoon ◽

Sea Surface ◽

Radiation Absorption ◽

Spatial And Temporal Variability ◽

Solar Absorption ◽

Chlorophyll Concentrations

Abstract. Chlorophyll has long been known to influence air–sea gas exchange and CO2 drawdown. But chlorophyll also influences regional climate through its effect on solar radiation absorption and thus sea surface temperature (SST). In the Bay of Bengal, the effect of chlorophyll on SST has been demonstrated to have a significant impact on the Indian summer (southwest) monsoon. However, little is known about the drivers and impacts of chlorophyll variability in the Bay of Bengal during the southwest monsoon. Here we use observations of downwelling irradiance measured by an ocean glider and three profiling floats to determine the spatial and temporal variability of solar absorption across the southern Bay of Bengal during the 2016 summer monsoon. A two-band exponential solar absorption scheme is fitted to vertical profiles of photosynthetically active radiation to determine the effective scale depth of blue light. Scale depths of blue light are found to vary from 12 m during the highest (0.3–0.5 mg m−3) mixed-layer chlorophyll concentrations to over 25 m when the mixed-layer chlorophyll concentrations are below 0.1 mg m−3. The Southwest Monsoon Current and coastal regions of the Bay of Bengal are observed to have higher mixed-layer chlorophyll concentrations and shallower solar penetration depths than other regions of the southern Bay of Bengal. Substantial sub-daily variability in solar radiation absorption is observed, which highlights the importance of near-surface ocean processes in modulating mixed-layer chlorophyll. Simulations using a one-dimensional K-profile parameterization ocean mixed-layer model with observed surface forcing from July 2016 show that a 0.3 mg m−3 increase in chlorophyll concentration increases sea surface temperature by 0.35 ∘C in 1 month, with SST differences growing rapidly during calm and sunny conditions. This has the potential to influence monsoon rainfall around the Bay of Bengal and its intraseasonal variability.

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