Vertical Analysis of Mesoscale Eddies in the Northern Bay of Bengal

2021 ◽  
Author(s):  
Abhijit Shee ◽  
Saikat Pramanik ◽  
Sourav Sil ◽  
Sudeep Das
Keyword(s):  
Chlorophyll A ◽  
Bay Of Bengal ◽  
Ecological Model ◽  
Mesoscale Eddies ◽  
Anticyclonic Eddy ◽  
Ocean Modeling ◽  
Height Anomaly ◽  
Regional Ocean Modeling System ◽  
Northern Bay Of Bengal ◽  
Anticyclonic Eddies

<p>Mesoscale eddies, coherent rotating structure with typical horizontal scale of ~100 km and temporal scales of a month, play a significant role in ocean energy and mass transports. Here both mesoscale cyclonic and anticyclonic eddies moving towards south in the northern Bay of Bengal during 20<sup>th </sup>March 2017 to 20<sup>th</sup> May 2017 are observed using a high resolution (~5 km) nitrogen-based nutrient, phytoplankton, zooplankton, and detritus (NPZD) ecological model embedded with Regional Ocean Modeling System (ROMS). Spatial maps of sea surface height anomaly (SSHA) from satellite-derived Archiving Validation, and Interpretation of Satellite Oceanographic (AVISO), and model are well matched. The centers and effective radii of both kind of eddies are identified using SSHA to proceed for their three-dimensional analysis. The extreme intensities of cyclonic and anticyclonic eddy centers are observed on 8<sup>th</sup> April 2017 at 86.40°E, 18.19°N and 84.80°E, 16.52°N respectively. Both kind of eddies are vertically extended upto 800 m and have radius ~100 km at surface. At these two locations, time-depth variations of zonal and meridional currents, and other physical (temperature and salinity) and bio-physical (chlorophyll-a, phytoplankton, zooplankton, detritus nutrient, dissolved oxygen and NO<sub>3</sub> nutrient) parameters are studied particularly from 8<sup>th</sup> March 2017 to 8<sup>th</sup> May 2017. Further vertical distribution of zonal and meridional currents, and other parameters are studied along the eddy diameters at their extreme intensity. In the vertical structure of both current components, an opposite sense between cyclonic and anticyclonic eddies are clearly captured, while other variables show strong upwelling and downwelling nature around the cyclonic and anticyclonic eddy centers respectively. Abundances (scarcities) of chlorophyll-a, phytoplankton, zooplankton and detritus nutrient are observed at 50 – 150 m depth of the cyclonic (anticyclonic) eddy center. The concentration of chlorophyll-a, phytoplankton, zooplankton and detritus nutrient reach to maximum of 1 mg/m<sup>3</sup>, 0.35 mMol/m<sup>3</sup>, 0.22 mMol/m<sup>3</sup> and 0.14 mMol/m<sup>3</sup> at ~80 m depth for the cyclonic eddy, while these are absent for the anticyclonic eddy.</p>

Seasonality of Submesoscale processes in the Bay of Bengal

2020 ◽  
Author(s):  
Lanman Li ◽  
Xuhua Cheng
Keyword(s):  
High Resolution ◽  
Mixed Layer ◽  
Bay Of Bengal ◽  
Gulf Stream ◽  
Strain Field ◽  
Mesoscale Eddies ◽  
Ocean Modeling ◽  
Small Scale ◽  
Regional Ocean Modeling System ◽  
Submesoscale Processes

<p>Mesoscale eddies that known as a dominant reservoir of kinetic energy has been studied extensively for its dynamics and variation.In order to maintain energy budget equilibrium,the energy stored in mesoscale eddies is dissipated by small scale processes around centimeters.Submesoscale processes that lie between mesoscale and microscale motions effectively extract energy from mesoscale motions and transfer to smaller scales.The Bay of Bengal(the BOB) receives large fresh water from precipitation and river runoff resulting in strong salinity fronts that conducive to the generation of submesoscale processes.Using the Regional Ocean Modeling System(ROMS) data with two horizontal resolutions:a high-resolution(~1.6km) that is partially resolve submesoscale,and a low-resolution(~7km) that not resolves submesoscale,we focus on the seasonality of submesoscale processes in the Bay of Bengal.To ensure that only the submesoscale motions is considered,we choose 40km as the length to separate submesoscale from the flow field.Results show that submesocale processes is ubiquitous in the BOB,mainly trapped in the mixed layer.As resolution increasing,submesoscale motions become much stronger.Seasonality of submesoscale in the BOB is apparent and is different from the Gulf stream region  which is strongest in winter and weakest in summer.Submesoscale features in this region mostly present in fall,which the most important mechanisms is frontogenesis due to strong horizontal buoyancy flux associated with large strain.Submesoscale motions is also vigorous in winter.The proposed mechanism is that the depth of mixed layer is deep enough which contributes to the occurrence of mixed layer instability.During the whole year,mesoscale strain field is weakest in summer,which makes submesoscale weakest.</p>

The impact of ocean data assimilation on the simulation of mesoscale eddies at São Paulo plateau (Brazil) using the regional ocean modeling system

2021 ◽  
pp. 101889
Author(s):  
Thiago Pires de Paula ◽  
Jose Antonio Moreira Lima ◽  
Clemente Augusto Souza Tanajura ◽  
Marcelo Andrioni ◽  
Renato Parkinson Martins ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Mesoscale Eddies ◽  
Sao Paulo ◽  
Ocean Modeling ◽  
São Paulo ◽  
Regional Ocean Modeling System ◽  
Ocean Data Assimilation ◽  
The Impact

scholarly journals A Lagrangian study of the contribution of the Canary coastal upwelling to the open North Atlantic nitrogen budget

2020 ◽  
Author(s):  
Derara Hailegeorgis ◽  
Zouhair Lachkar ◽  
Christoph Rieper ◽  
Nicolas Gruber
Keyword(s):  
North Atlantic ◽  
Inorganic Nitrogen ◽  
Mesoscale Eddies ◽  
Ocean Modeling ◽  
Regional Ocean Modeling System ◽  
The North ◽  
Dominant Feature ◽  
Canary Upwelling ◽  
The North Atlantic ◽  
Offshore Transport

Abstract. The Canary Current System (CanCS) is a major Eastern Boundary Upwelling System (EBUS), known for its high nearshore productivity and for sustaining large fisheries. Only a part of the inorganic nutrients that upwell along Northwest Africa are being used to fuel the high nearshore productivity. The remainder together with some of the newly formed organic nutrients are exported offshore into the adjacent oligotrophic subtropical gyre of the North Atlantic. Yet, the offshore reach of these nutrients and their importance for the biogeochemistry of the open North Atlantic is not yet fully quantified. Here, we determine the lateral transport of both organic and inorganic nitrogen from the Canary upwelling and investigate the timescales, reach, and structure of offshore transport using a Lagrangian modelling approach. To this end, we track all water parcels entering the coastal ocean and upwelling along the Northwest African coast between 14° N and 35° N, as simulated by an eddy-resolving configuration of the Regional Ocean Modeling System (ROMS). Our model analysis suggests that the vast majority of the upwelled waters originate from offshore and below the euphotic zone (70 m depth), and once upwelled remain in the top 100 m. The offshore transport is intense, yet it varies greatly along the coast. The central CanCS (21° N–28° N) transports the largest amount of water offshore, thanks to a larger upwelling volume and a faster offshore transport. In contrast, the southern CanCS (14° N–21° N) exports more nitrogen from the nearshore, primarily because of the higher nitrogen-content of its upwelling waters. Beyond 200 km, this nitrogen offshore transport declines rapidly because the shallow depth of most water parcels supports high organic matter formation and subsequent export of the organic nitrogen to depth. The horizontal pattern of offshore transport is characterized by latitudinally alternating offshore-onshore corridors indicating a strong contribution of mesoscale eddies and filaments to the mean transport. Around 1/3 of the total offshore transport of water occurs around major capes along the CanCS. The persistent filaments associated with these capes are responsible for an up to four-fold enhancement of the offshore transport of water and nitrogen in the first 400 km. Much of this water and nitrogen stems from upwelling at quite some distance from the capes, confirming the capes' role in collecting water from along the coast. North of Cape Blanc and within the first 500 km from the coast, water recirculation is a dominant feature of offshore transport. This process, likely associated with mesoscale eddies, tends to reduce the efficiency of offshore transport. This process is less important in the southern CanCS along the Mauritanian coast. The Canary upwelling is modelled to supply around 44 mmol N m−2 yr−1 and 7 mmol N m−2 yr−1 to the North Atlantic Tropical Gyral (NATR) and the North Atlantic Subtropical Gyral East (NASE) Longhurst provinces, respectively. In the NATR, this represents nearly half (45 ± 15 %) of the estimated total new production, while in the NASE, this fraction is small (3.5 ± 1.5 %). Our results highlight the importance of the CanCS upwelling as a key source of nutrient to the open North Atlantic and stress the need for improving the representation of EBUS in global coarse resolution models.

scholarly journals Multi-Source Data Analysis of Mesoscale Eddies and Their Effects on Surface Chlorophyll in the Bay of Bengal

2020 ◽  
Vol 12 (21) ◽  
pp. 3485
Author(s):  
Xiao Yang ◽  
Guangjun Xu ◽  
Yu Liu ◽  
Wenjin Sun ◽  
Changshui Xia ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Bay Of Bengal ◽  
Cold Water ◽  
Mesoscale Eddies ◽  
Sea Surface ◽  
Wind Fields ◽  
Local Current ◽  
Source Data ◽  
Eddy Generation ◽  
Anticyclonic Eddies

Mesoscale eddies are important to ocean circulation due to their roles in the transport of mass, energy, and heat. This study employs a combination of data sources to initiate a statistical analysis of eddy spatiotemporal characteristics in the Bay of Bengal (BOB) to elucidate the sea surface and vertical structures of the eddies and their impacts on sea surface chlorophyll (Chl) distributions. The results suggest that 1237 cyclonic eddies (CEs) and 1121 anticyclonic eddies (AEs) were detected in 26 years. The number of two eddy polarities was almost the same, and most of them spread to the west or southwest direction. The vertical change of temperature (T) and salinity (S) caused by the eddies is studied and the anomalous eddies, i.e., a CE (AE) eddy with warm (cold) water at the center, are mainly distributed on the northeast side of the Island of Sri Lanka. Furthermore, CEs are found to increase Chl concentration in the surrounding sea by approximately 11.15%, while AEs decrease concentrations also by approximately 11.25%. Changes in Chl concentrations occur most rapidly during the mature and intensification eddy phases. Observations also indicate that the strong local current and wind fields are the primary mechanisms in eddy generation.

scholarly journals Corrigendum to “The impact of ocean data assimilation on the simulation of mesoscale eddies at São Paulo plateau (Brazil) using the regional ocean modeling system” [Ocean Model. 167 (2021) 101889]

2022 ◽  
Vol 169 ◽  
pp. 101918
Author(s):  
Thiago Pires de Paula ◽  
Jose Antonio Moreira Lima ◽  
Clemente Augusto Souza Tanajura ◽  
Marcelo Andrioni ◽  
Renato Parkinson Martins ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Mesoscale Eddies ◽  
Ocean Model ◽  
Sao Paulo ◽  
Ocean Modeling ◽  
São Paulo ◽  
Regional Ocean Modeling System ◽  
Ocean Data Assimilation ◽  
The Impact

On the evolution of the northern Bay of Bengal Dome.

2021 ◽  
Author(s):  
Anup Nambiathody ◽  
Vijith Vijayakumaran ◽  
Abhisek Chatterjee
Keyword(s):  
Summer Monsoon ◽  
Bay Of Bengal ◽  
Nutrient Budget ◽  
Small Region ◽  
Height Anomaly ◽  
Biogeochemical Model ◽  
Wind Stress Curl ◽  
Near Surface ◽  
The North ◽  
Northern Bay Of Bengal

<p>The climatologically averaged sea surface height anomaly (SSHA) during the summer monsoon in the Bay of Bengal (BoB) shows two prominent negative anomalies, one in the southern BoB and another in the northern BoB. The occurrence of negative SSHA observed in the southern BoB has been extensively studied and is linked to Sri Lanka Dome (SLD), whereas negative SSHA observed in the north has received less attention. A pronounced thermal dome develops in the northern BoB with its mean position between 86-89<sup>o</sup>E and 16-19<sup>o</sup>N, as shown by the doming of isotherms. We refer to this oceanic thermal dome as the northern BoB Dome (NBD). The present study focuses on the evolution of the NBD using observation and a coupled OGCM-biogeochemical model. The formation of NBD occurs during the summer monsoon (May - September), at a time when the wind stress curl is positive. Interestingly, the cyclonic curl is positive in the entire northern BoB, yet the negative SSHA is confined to a small region. Our analysis shows that strong stratification in the northern BoB inhibits the entrainment of the cooler-nutrient-rich subsurface waters to the surface during the event of dome formation. Consequently, the mixed-layer temperature in the NBoB region stays above the temperature criteria for active convection (>28 <sup>o</sup>C). Further, the inhibition of entrainment of nutrients causes the NBD region to be lower in productivity than the SLD region, as seen in chlorophyll distribution. We compare the NBD's heat and nutrient budget with the SLD and show that the near-surface stratification differences make the two domes distinct from each other.</p>

Statistical characteristics and thermohaline properties of mesoscale eddies in the Bay of Bengal

2021 ◽  
Vol 40 (4) ◽  
pp. 10-22
Author(s):  
Wei Cui ◽  
Chaojie Zhou ◽  
Jie Zhang ◽  
Jungang Yang
Keyword(s):  
Bay Of Bengal ◽  
Mesoscale Eddies ◽  
Statistical Characteristics
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