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>

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>

scholarly journals Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 553 ◽  
Author(s):  
Yongchui Zhang ◽  
Xi Chen ◽  
Changming Dong
Keyword(s):  
High Resolution ◽  
Mixed Layer ◽  
Kuroshio Extension ◽  
Mesoscale Eddies ◽  
Cyclonic Eddy ◽  
Intermediate Water ◽  
Dipole Structure ◽  
Significant Difference ◽  
The Kuroshio ◽  
Main Thermocline

Mesoscale eddies are common in the ocean and their surface characteristics have been well revealed based on altimetric observations. Comparatively, the knowledge of the three-dimensional (3D) structure of mesoscale eddies is scarce, especially in the open ocean. In the present study, high-resolution field observations of a cyclonic eddy in the Kuroshio Extension have been carried out and the anatomy of the observed eddy is conducted. The temperature anomaly exhibits a vertical monopole cone structure with a maximum of −7.3 °C located in the main thermocline. The salinity anomaly shows a vertical dipole structure with a fresh anomaly in the main thermocline and a saline anomaly in the North Pacific Intermediate Water (NPIW). The cyclonic flow displays an equivalent barotropic structure. The mixed layer is deep in the center of the eddy and thin in the periphery. The seasonal thermocline is intensified and the permanent thermocline is upward domed by 350 m. The subtropical mode water (STMW) straddled between the seasonal and permanent thermoclines weakens and dissipates in the eddy center. The salinity of NPIW distributed along the isopycnals shows no significant difference inside and outside the eddy. The geostrophic relation is approximately set up in the eddy. The nonlinearity—defined as the ratio between the rotational speed to the translational speed—is 12.5 and decreases with depth. The eddy-wind interaction is examined by high resolution satellite observations. The results show that the cold eddy induces wind stress aloft with positive divergence and negative curl. The wind induced upwelling process is responsible for the formation of the horizontal monopole pattern of salinity, while the horizontal transport results in the horizontal dipole structure of temperature in the mixed layer.

scholarly journals Multi-Physics Ensemble versus Atmosphere–Ocean Coupled Model Simulations for a Tropical-Like Cyclone in the Mediterranean Sea

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 202 ◽  
Author(s):  
Antonio Ricchi ◽  
Mario Marcello Miglietta ◽  
Davide Bonaldo ◽  
Guido Cioni ◽  
Umberto Rizza ◽  
...  
Keyword(s):  
High Resolution ◽  
Mediterranean Sea ◽  
Computational Cost ◽  
Ocean Model ◽  
Surface Fluxes ◽  
Ocean Modeling ◽  
Sea Surface ◽  
Regional Ocean Modeling System ◽  
The Mediterranean ◽  
Physics Ensemble

Between 19 and 22 January 2014, a baroclinic wave moving eastward from the Atlantic Ocean generated a cut-off low over the Strait of Gibraltar and was responsible for the subsequent intensification of an extra-tropical cyclone. This system exhibited tropical-like features in the following stages of its life cycle and remained active for approximately 80 h, moving along the Mediterranean Sea from west to east, eventually reaching the Adriatic Sea. Two different modeling approaches, which are comparable in terms of computational cost, are analyzed here to represent the cyclone evolution. First, a multi-physics ensemble using different microphysics and turbulence parameterization schemes available in the WRF (weather research and forecasting) model is employed. Second, the COAWST (coupled ocean–atmosphere wave sediment transport modeling system) suite, including WRF as an atmospheric model, ROMS (regional ocean modeling system) as an ocean model, and SWAN (simulating waves in nearshore) as a wave model, is used. The advantage of using a coupled modeling system is evaluated taking into account air–sea interaction processes at growing levels of complexity. First, a high-resolution sea surface temperature (SST) field, updated every 6 h, is used to force a WRF model stand-alone atmospheric simulation. Later, a two-way atmosphere–ocean coupled configuration is employed using COAWST, where SST is updated using consistent sea surface fluxes in the atmospheric and ocean models. Results show that a 1D ocean model is able to reproduce the evolution of the cyclone rather well, given a high-resolution initial SST field produced by ROMS after a long spin-up time. Additionally, coupled simulations reproduce more accurate (less intense) sea surface heat fluxes and a cyclone track and intensity, compared with a multi-physics ensemble of standalone atmospheric simulations.

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 Diagnosis of the Vertical Motions in a Mesoscale Stirring Region

2007 ◽  
Vol 37 (5) ◽  
pp. 1413-1424 ◽  
Author(s):  
Cédric Legal ◽  
Patrice Klein ◽  
Anne-Marie Treguier ◽  
Jerome Paillet
Keyword(s):  
High Resolution ◽  
Velocity Field ◽  
Vertical Velocity ◽  
Mesoscale Eddies ◽  
Altimeter Data ◽  
Small Scale ◽  
Thin Structures ◽  
Numerical Studies ◽  
Northeast Atlantic Ocean ◽  
Ocean Models

Abstract A high-resolution survey was conducted as part of the 2001 Programme Ocean Multidisciplinaire Meso Echelle (POMME 2) experiment in a region of the northeast Atlantic Ocean characterized by a large number of strongly interacting mesoscale eddies. The survey was located between mesoscale eddies in an area where the horizontal stirring processes were dominant. Diagnosis, using SeaSoar data combined with the analysis of altimeter data, reveals an energetic vertical velocity field involving elongated thin structures with alternate signs and amplitude up to 20 m day−1. The 3D dynamics involved in the appearance of these vertical motions is the restoration of the thermal wind balance within the small-scale density filaments that are elongated by the stirring processes. These experimental results reinforce the conclusions of previous numerical studies pointing out the necessity to explicitly include the effects of the filamentation process in ocean models.

scholarly journals High-Resolution Operational Ocean Forecast and Reanalysis System for the Indian Ocean

2020 ◽  
Vol 101 (8) ◽  
pp. E1340-E1356 ◽  
Author(s):  
P. A. Francis ◽  
A. K. Jithin ◽  
J. B. Effy ◽  
A. Chatterjee ◽  
K. Chakraborty ◽  
...  
Keyword(s):  
High Resolution ◽  
Indian Ocean ◽  
Data Assimilation ◽  
Coastal Waters ◽  
General Circulation ◽  
High Performance ◽  
Coast Guard ◽  
Ocean Modeling ◽  
Regional Ocean Modeling System ◽  
The Indian Ocean

Abstract A good understanding of the general circulation features of the oceans, particularly of the coastal waters, and ability to predict the key oceanographic parameters with good accuracy and sufficient lead time are necessary for the safe conduct of maritime activities such as fishing, shipping, and offshore industries. Considering these requirements and buoyed by the advancements in the field of ocean modeling, data assimilation, and ocean observation networks along with the availability of the high-performance computational facility in India, Indian National Centre for Ocean Information Services has set up a “High-Resolution Operational Ocean Forecast and Reanalysis System” (HOOFS) with an aim to provide accurate ocean analysis and forecasts for the public, researchers, and other types of users like navigators and the Indian Coast Guard. Major components of HOOFS are (i) a suite of numerical ocean models configured for the Indian Ocean and the coastal waters using the Regional Ocean Modeling System (ROMS) for forecasting physical and biogeochemical state of the ocean and (ii) the data assimilation based on local ensemble transform Kalman filter that assimilates in situ and satellite observations in ROMS. Apart from the routine forecasts of key oceanographic parameters, a few important applications such as (i) Potential Fishing Zone forecasting system and (ii) Search and Rescue Aid Tool are also developed as part of the HOOFS project. The architecture of HOOFS, an account of the quality of ocean analysis and forecasts produced by it and important applications developed based on HOOFS are briefly discussed in this article.

scholarly journals Mixed layer sub-mesoscale parameterization – Part 1: Derivation and assessment

Ocean Science ◽  
2010 ◽  
Vol 6 (3) ◽  
pp. 679-693 ◽  
Author(s):  
V. M. Canuto ◽  
M. S. Dubovikov
Keyword(s):  
High Resolution ◽  
Mixed Layer ◽  
Wind Direction ◽  
Small Scale ◽  
Mean Flow ◽  
Mean Velocity ◽  
Geostrophic Velocity ◽  
Global Circulation Models ◽  
The Mean ◽  
Strong Winds

Abstract. Several studies have shown that sub-mesoscales (SM ~1 km horizontal scale) play an important role in mixed layer dynamics. In particular, high resolution simulations have shown that in the case of strong down-front wind, the re-stratification induced by the SM is of the same order of the de-stratification induced by small scale turbulence, as well as of that induced by the Ekman velocity. These studies have further concluded that it has become necessary to include SM in ocean global circulation models (OGCMs), especially those used in climate studies. The goal of our work is to derive and assess an analytic parameterization of the vertical tracer flux under baroclinic instabilities and wind of arbitrary directions and strength. To achieve this goal, we have divided the problem into two parts: first, in this work we derive and assess a parameterization of the SM vertical flux of an arbitrary tracer for ocean codes that resolve mesoscales, M, but not sub-mesoscales, SM. In Part 2, presented elsewhere, we have used the results of this work to derive a parameterization of SM fluxes for ocean codes that do not resolve either M or SM. To carry out the first part of our work, we solve the SM dynamic equations including the non-linear terms for which we employ a closure developed and assessed in previous work. We present a detailed analysis for down-front and up-front winds with the following results: (a) down-front wind (blowing in the direction of the surface geostrophic velocity) is the most favorable condition for generating vigorous SM eddies; the de-stratifying effect of the mean flow and re-stratifying effect of SM almost cancel each other out, (b) in the up-front wind case (blowing in the direction opposite to the surface geostrophic velocity), strong winds prevents the SM generation while weak winds hinder the process but the eddies amplify the re-stratifying effect of the mean velocity, (c) wind orthogonal to the geostrophic velocity. In this case, which was not considered in numerical simulations, we show that when the wind direction coincides with that of the horizontal buoyancy gradient, SM eddies are generated and their re-stratifying effect partly cancels the de-stratifying effect of the mean velocity. The case when wind direction is opposite to that of the horizontal buoyancy gradient, is analogous to the case of up-front winds. In conclusion, the new multifaceted implications on the mixed layer stratification caused by the interplay of both strength and directions of the wind in relation to the buoyancy gradient disclosed by high resolution simulations have been reproduced by the present model. The present results can be used in OGCMs that resolve M but not SM.

scholarly journals Gulf Stream Dynamics along the Southeastern U.S. Seaboard

2015 ◽  
Vol 45 (3) ◽  
pp. 690-715 ◽  
Author(s):  
Jonathan Gula ◽  
M. Jeroen Molemaker ◽  
James C. McWilliams
Keyword(s):  
Gulf Stream ◽  
Ocean Modeling ◽  
Mean Flow ◽  
Regional Ocean Modeling System ◽  
Meridional Transport ◽  
Local Pressure ◽  
Straits Of Florida ◽  
Eddy Fluxes ◽  
The Mean ◽  
Mean Current

AbstractThe Gulf Stream strongly interacts with the topography along the southeastern U.S. seaboard, between the Straits of Florida and Cape Hatteras. The dynamics of the Gulf Stream in this region is investigated with a set of realistic, very high-resolution simulations using the Regional Ocean Modeling System (ROMS). The mean path is strongly influenced by the topography and in particular the Charleston Bump. There are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward. The topography provides, through bottom pressure torque, the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre-scale vorticity balance. The effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow. The baroclinic instability is stabilized by the slope everywhere except past the bump. The flow is barotropically unstable, and kinetic energy is converted from the mean flow to the eddies following the Straits of Florida and at the bump with regions of eddy-to-mean conversion in between. There is eddy growth by Reynolds stress and downstream development of the eddies. Interaction of the flow with the topography acts as an external forcing process to localize these oceanic storm tracks. Associated time-averaged eddy fluxes are essential to maintain and reshape the mean current. The pattern of eddy fluxes is interpreted in terms of eddy life cycle, eddy fluxes being directed downgradient in eddy growth regions and upgradient in eddy decay regions.

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.

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