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

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.

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Observed Warm Filaments from the Kuroshio Associated with Mesoscale Eddies

Remote Sensing ◽

10.3390/rs12183090 ◽

2020 ◽

Vol 12 (18) ◽

pp. 3090

Author(s):

Qian Shi ◽

Guihua Wang

Keyword(s):

High Frequency ◽

Average Length ◽

Mesoscale Eddies ◽

Satellite Observations ◽

Sea Surface ◽

Large Temperature ◽

Anticyclonic Eddies ◽

The Kuroshio ◽

Sst Gradient

Based on high resolution satellite observations of sea surface temperature (SST), warm filaments near the Kuroshio around the Luzon Strait were systematically identified. These filaments extend an average length of about 200 km from the Kuroshio. The occurrence and features of the warm filaments are highly associated with both mesoscale eddies and the intensity of the SST gradient of the Kuroshio. Warm filaments are formed by heat advection from the warm Kuroshio into the colder interior Pacific Ocean by anticyclonic eddies (∼58%), cyclonic eddies (∼10%), and the dipole eddies (∼16%). The large temperature gradient near the Batanes Islands may also contribute to the high frequency of warm filaments in their vicinity. This study will help elucidate the role of zonal heat transport associated with the Kuroshio–eddy interaction during filament formation.

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Vertical Analysis of Mesoscale Eddies in the Northern Bay of Bengal

10.5194/egusphere-egu21-14983 ◽

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

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 20th March 2017 to 20th 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 8th April 2017 at 86.40&#176;E, 18.19&#176;N and 84.80&#176;E, 16.52&#176;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 NO3 nutrient) parameters are studied particularly from 8th March 2017 to 8th 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 &#8211; 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/m3, 0.35 mMol/m3, 0.22 mMol/m3 and 0.14 mMol/m3 at ~80 m depth for the cyclonic eddy, while these are absent for the anticyclonic eddy.

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Statistical Assessment of Sea-Surface Salinity from SMAP: Arabian Sea, Bay of Bengal and a Promising Red Sea Application

Remote Sensing ◽

10.3390/rs12030447 ◽

2020 ◽

Vol 12 (3) ◽

pp. 447 ◽

Cited By ~ 3

Author(s):

Viviane V. Menezes

Keyword(s):

Red Sea ◽

Ocean Circulation ◽

Bay Of Bengal ◽

Arabian Sea ◽

Hydrological Cycle ◽

North Indian Ocean ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

The North

Sea-surface salinity (SSS) is an essential climate variable connected to Earth’s hydrological cycle and a dynamical component of ocean circulation, but its variability is not well-understood. Thanks to Argo floats, and the first decade of salinity remote sensing, this is changing. While satellites can retrieve salinity with some confidence, accuracy is regionally dependent and challenging within 500–1000 km offshore. The present work assesses the first four years of the National Aeronautics and Space Administration’s Soil Moisture Active Passive (SMAP) satellite in the North Indian Ocean. SMAP’s improved spatial resolution, better mitigation for radio-frequency interference, and land contamination make it particularly attractive to study coastal areas. Here, regions of interest are the Bay of Bengal, the Arabian Sea, and the extremely salty Red Sea (the last of which has not yet received attention). Six SMAP products, which include Levels 2 and 3 data, were statistically evaluated against in situ measurements collected by a variety of instruments. SMAP reproduced SSS well in both the Arabian Sea and the Bay of Bengal, and surprisingly well in the Red Sea. Correlations there were 0.81–0.93, and the root-mean-square difference was 0.38–0.67 for Level 3 data.

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Eddies and their energetics in the Bay of Bengal

10.5194/egusphere-egu2020-1879 ◽

2020 ◽

Author(s):

Navin Chandra ◽

Vimlesh Pant

Keyword(s):

Kinetic Energy ◽

Ocean Circulation ◽

Bay Of Bengal ◽

Cold Water ◽

Thermal Structure ◽

Thermodynamic Characteristics ◽

Surface Current ◽

Ocean Model ◽

Coastal Current ◽

Current Pattern

Eddies are integral part of ocean circulation. They play an important role in energy transfer. The surface kinetic energy in eddies can be ten times higher than the energy of the current through which these are generated. Eddies influence the thermodynamic characteristics of the upper-ocean. Oceanic eddies trap and transport hot (cold) water in the core of an anticyclonic (cyclonic) eddy. Therefore, these eddies can modify the thermal structure by the advection of temperature anomalies and its subsequent mixing. Generation of eddies takes place mainly due to the baroclinic instability of the ocean. However, some of the eddies may form due to coastal and bathymetrical geometry. The Bay of Bengal (BoB) is an enclosed basin in the northern Indian Ocean (IO). The BoB exhibits unique physical and dynamical properties due to surplus low-saline waters and shallow mixed layer. It observes seasonal variation of wind and changes in the surface current pattern. Major rivers originating from the Himalayan glaciers drain into the BoB throughout the year with a peak in July-October. The riverine freshwater together with strong post-monsoon (October-November) coastal current generate complex and turbulent surface current pattern with a large number of eddies in the BoB. The wind forcing, coastal currents, and bathymetry make favorable conditions for the generation of eddies in the BoB. In the present study, a numerical ocean model Regional Ocean Modelling System (ROMS) used to simulate the mesoscale eddies in the BoB. The ROMS model uses sigma vertical coordinates which helps in taking account of the effects of coastal and bathymetrical structures on surface circulation and eddy generation. The model results are verified with the available observations. For the detection and tracking of eddies at the surface, both the geometrical and dynamical methods are used. The geometrical method is based on the identification of local minima and maxima of dynamic sea surface height. Whereas, the dynamical method utilizes current turbulences arising from strain or vorticity to identify eddies. Using model simulations, the cyclonic and anticyclonic eddies are identified in the BoB. The life span (time period) and the kinetic energy of individual eddies are calculated. The spatial and temporal distribution of eddies and their energetics in the BoB are discussed. Further, the propagation tracks of individual eddies are estimated.

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Generation and Stability of a Quasi-Permanent Vortex in the Lofoten Basin

Journal of Physical Oceanography ◽

10.1175/2007jpo3694.1 ◽

2007 ◽

Vol 37 (11) ◽

pp. 2637-2651 ◽

Cited By ~ 55

Author(s):

Armin Köhl

Keyword(s):

Ocean Circulation ◽

Large Scale ◽

Cold Water ◽

Circulation Model ◽

Feedback Mechanism ◽

Generation Mechanism ◽

Altimeter Data ◽

Positive Feedback Mechanism ◽

The Stability ◽

Anticyclonic Eddies

Abstract In the Nordic seas the Lofoten Basin is a region of high mesoscale activity. The generation mechanism and the conditions for the stability of a quasi-permanent vortex in the center of the Lofoten Basin are studied with a high-resolution ocean circulation model and altimeter data. The vortex and its generation mechanism manifest themselves by a pronounced sea surface height (SSH) signature and variability, which are found to be in agreement with altimeter data. The vortex results primarily from anticyclonic eddies shed from the eastern branch of the Norwegian Atlantic Current, which propagate southwestward. The large-scale bottom depression of the Lofoten Basin plays a crucial role for attracting anticyclones into the trough and for enabling the dynamical stability of the vortex. The water mass characteristics of the anticyclone lead to enhanced atmospheric interaction (heat loss) during wintertime. The cold water trapped in the upper part of the vortex preconditions convection in the following winter. This positive feedback mechanism tends to deepen convection progressively within the upper part of the vortex.

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

Acta Oceanologica Sinica ◽

10.1007/s13131-021-1723-4 ◽

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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Spatiotemporal Variability of Mesoscale Eddies in the Indonesian Seas

Remote Sensing ◽

10.3390/rs13051017 ◽

2021 ◽

Vol 13 (5) ◽

pp. 1017

Author(s):

Zhanjiu Hao ◽

Zhenhua Xu ◽

Ming Feng ◽

Qun Li ◽

Baoshu Yin

Keyword(s):

World Ocean ◽

Mesoscale Eddies ◽

Spatial Inhomogeneity ◽

Spatiotemporal Variability ◽

Identification Algorithm ◽

Mean Flow ◽

Sulu Sea ◽

Indonesian Seas ◽

Highly Nonlinear ◽

Eddy Generation

Mesoscale eddies are ubiquitous in the world ocean and well researched both globally and regionally, while their properties and distributions across the whole Indonesian Seas are not yet fully understood. This study investigates for the first time the spatiotemporal variations and generation mechanisms of mesoscale eddies across the whole Indonesian Seas. Eddies are detected from altimetry sea level anomalies by an automatic identification algorithm. The Sulu Sea, Sulawesi Sea, Maluku Sea and Banda Sea are the main eddy generation regions. More than 80% of eddies are short-lived with a lifetime below 30 days. The properties of eddies exhibit high spatial inhomogeneity, with the typical amplitudes and radiuses of 2–6 cm and 50–160 km, respectively. The most energetic eddies are observed in the Sulawesi Sea and Seram Sea. Eddies feature different seasonal cycles between anticyclonic and cyclonic eddies in each basin, especially given that the average latitude of the eddy centroid has inverse seasonal variations. About 48% of eddies in the Sulawesi Sea are highly nonlinear, which is the case for less than 30% in the Sulu Sea and Banda Sea. Instability analysis is performed using high-resolution model outputs from Bluelink Reanalysis to assess mechanisms of eddy generation. Barotropic instability of the mean flow dominates eddy generation in the Sulu Sea and Sulawesi Sea, while baroclinic instability is slightly more in the Maluku Sea and Banda Sea.

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Wind-Driven Response of the Northern Indian Ocean to Climate Extremes*

Journal of Climate ◽

10.1175/jcli4150.1 ◽

2007 ◽

Vol 20 (13) ◽

pp. 2978-2993 ◽

Cited By ~ 22

Author(s):

Tommy G. Jensen

Keyword(s):

Indian Ocean ◽

Ocean Circulation ◽

Bay Of Bengal ◽

El Niño ◽

Arabian Sea ◽

El Nino ◽

Ocean Model ◽

La Niña ◽

Northern Indian Ocean ◽

La Nina

Abstract Composites of Florida State University winds (1970–99) for four different climate scenarios are used to force an Indian Ocean model. In addition to the mean climatology, the cases include La Niña, El Niño, and the Indian Ocean dipole (IOD). The differences in upper-ocean water mass exchanges between the Arabian Sea and the Bay of Bengal are investigated and show that, during El Niño and IOD years, the average clockwise Indian Ocean circulation is intensified, while it is weakened during La Niña years. As a consequence, high-salinity water export from the Arabian Sea into the Bay of Bengal is enhanced during El Niño and IOD years, while transport of low-salinity waters from the Bay of Bengal into the Arabian Sea is enhanced during La Niña years. This provides a venue for interannual salinity variations in the northern Indian Ocean.

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