Estimations of vertical diffusivity and applications on a mixed layer budget analysis of the Bay of Bengal using Argo data

Shee, Abhijit; Sil, Sourav

doi:10.1016/j.jmarsys.2023.103857

Cited by 8 publications

(4 citation statements)

References 69 publications

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“…However, particle paths intersected the periphery of the wind-elongated dye patch, leading to a slight deviation of trajectories predicted by HF radar from those of the dye patch. This discrepancy arises because the dye patch diffuses across a broader depth, ex- The estimation of vertical eddy diffusivity (1.9 × 10 −4 m 2 /s), which to the best of our knowledge is the first measurement near the ocean surface based on scalar mixing measurements, is an order of magnitude higher than those observed at the base of the ocean mixed layer in the Bay of Bengal as measured by Argo data [61]. Other estimates show K z in much of the ocean's interior to be around 10 −5 m 2 /s based on scalar mixing and microstructure experiments [21,[62][63][64].…”

Section: Horizontal Dispersion and Vertical Mixing Of Tracersmentioning

confidence: 77%

Near-Surface Dispersion and Current Observations Using Dye, Drifters, and HF Radar in Coastal Waters

Kim,

Tran,

Song

et al. 2024

Remote Sensing

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This study explores the near-surface dispersion mechanisms of contaminants in coastal waters, leveraging a comprehensive method that includes using dye and drifters as tracers, coupled with diverse observational platforms like drones, satellites, in situ sampling, and HF radar. The aim is to deepen our understanding of surface currents’ impact on contaminant dispersion, thereby improving predictive models for managing environmental incidents such as pollutant releases. Rhodamine WT dye, chosen for its significant fluorescent properties and detectability, along with drifter data, allowed us to investigate the dynamics of near-surface physical phenomena such as the Ekman current, Stokes drift, and wind-driven currents. Our research emphasizes the importance of integrating scalar tracers and Lagrangian markers in experimental designs, revealing differential dispersion behaviors due to near-surface vertical shear caused by the Ekman current and Stokes drift. During slow-current conditions, the elongation direction of the dye patch aligned well with the direction of a depth-averaged Ekman spiral, or Ekman transport. Analytical calculations of vertical shear, based on the Ekman current and Stokes drift, closely matched those derived from tracer observations. Over a 7 h experiment, the vertical diffusivity near the surface was first observed at the early stages of scalar mixing, with a value of 1.9×10−4 m2/s, and the horizontal eddy diffusivity of the dye patch and drifters reached the order of 1 m2/s at a 1000 m length scale. Particle tracking models demonstrate that while HF radar currents can effectively predict the trajectories of tracers near the surface, incorporating near-surface currents, including the Ekman current, Stokes drift, and windage, is essential for a more accurate prediction of the fate of surface floats.

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Section: Horizontal Dispersion and Vertical Mixing Of Tracersmentioning

confidence: 77%

Near-Surface Dispersion and Current Observations Using Dye, Drifters, and HF Radar in Coastal Waters

Kim,

Tran,

Song

et al. 2024

Remote Sensing

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“…This feature caused haline stratification over the region, resulting in a stable upper surface with a high heat content. Several earlier studies (Mandal et al., 2020) have reported increased stratification during winter in the northern bay, attributed to increased vertical diffusion and a warming trend in the subsurface (Shee & Sil, 2023). In the case of Yaas, freshwater plumes persisted in the northern region until the beginning of May, affecting both surface and subsurface layers, which enhance the vertical diffusion and cause the related warming in the upper surface.…”

Section: Discussionmentioning

confidence: 94%

Role of Anomalous Ocean Warming on the Intensification of Pre‐Monsoon Tropical Cyclones Over the Northern Bay of Bengal

Ray,

Das,

Sil

2024

JGR Oceans

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The northern Indian Ocean, typically the Bay of Bengal (BoB), has experienced several stronger tropical cyclones during the pre‐monsoon season in the last few years. Similarly, in 2021, cyclone Yaas reached the Very Severe Cyclonic Storm (VSCS) stage despite forming above 14°N. In comparison to the other three cyclones that formed in 2007 (Akash), 2009 (Aila), and 2017 (Mora) with a similar cyclogenesis location and track, the pre‐cyclonic condition in 2021 is more favorable. It was found that from 2007 to 2021, the area associated with Sea Surface Temperature greater than 31°C increased from 0.1 percent to 29 percent. The Research Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction buoy at 15°N also recorded an increasing trend of 0.1°C per year in both average and maximum temperatures during May. The warming in 2021 is primarily linked with Marine Heat Wave events, which extensively cover the north BoB for a longer duration starting from the first week of May. Such warming extends even to the subsurface, providing the heat required to convert the depression into VSCS within 2 days. The weaker western boundary current during 2021 made the northern BoB fresher and favorable for cyclone, intensification. The associated anticyclonic eddy along the track extended the abnormal distribution of low saline water even up to the subsurface (∼100m), which is vital in increasing the ocean heat content. These simultaneous pre‐cyclonic oceanic conditions can be incorporated into the weather model to understand and predict the rapid intensification within a shorter duration.

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“…The vertical eddy diffusivity, calculated from the variance differences (𝜎 − 𝜎 ) over time (𝐾 = 0.25(𝜎 − 𝜎 )/∆𝑡), was determined to be 1.91 × 10 𝑚 /𝑠. This estimate, focused on the top surface layer, indicates a vertical diffusivity coefficient significantly higher than those observed at deeper depths, highlighting enhanced mixing near the surface [46] even under mild weather conditions.…”

Section: Vertical Dye Distributionmentioning

confidence: 88%

Near-Surface Dispersion and Current Observations by Dye, Drifter, and HF Radar in Coastal Water

Kim,

Hong,

Song

et al. 2024

Preprint

View full text Add to dashboard Cite

This study explores the near-surface dispersion mechanisms of contaminants in coastal waters, leveraging a comprehensive method that includes using dye and drifters as tracers, coupled with diverse observational platforms like drones, satellites, in-situ sampling, and HF radar. The aim is to deepen our understanding of surface currents' impact on contaminant dispersion, thereby improving predictive models for environmental incident management, including pollutant releases. Rhodamine WT dye, chosen for its significant fluorescent properties and detectability, along with drifter data, allowed us to investigate the dynamics of near-surface physical phenomena such as the Ekman current, Stokes drift, and wind-driven currents. Our research emphasizes the importance of integrating scalar tracers and Lagrangian markers in experimental designs, revealing differential dispersion behaviors due to near-surface vertical shear caused by the Ekman current and Stokes drift. The elongation direction of the dye patch aligns with the Ekman current direction during slow current conditions. Analytical calculations of vertical shear, based on the Ekman current and Stokes drift, closely matched those derived from tracer observations. Over a 7-hour experiment, the vertical diffusivity of near-surface water was observed at 2×10-4 m2/s, and the horizontal eddy diffusivity of the dye patch and drifters reached the order of 1 m2/s and at a 1000m length scale. Particle tracking models demonstrate that while HF radar currents can effectively predict the trajectories of tracers near the surface, incorporating near-surface currents, including Ekman current, Stokes drift, and windage, is essential for a more accurate prediction of the fate of surface floats.

show abstract

Estimations of vertical diffusivity and applications on a mixed layer budget analysis of the Bay of Bengal using Argo data

Cited by 8 publications

References 69 publications

Near-Surface Dispersion and Current Observations Using Dye, Drifters, and HF Radar in Coastal Waters

Near-Surface Dispersion and Current Observations Using Dye, Drifters, and HF Radar in Coastal Waters

Role of Anomalous Ocean Warming on the Intensification of Pre‐Monsoon Tropical Cyclones Over the Northern Bay of Bengal

Near-Surface Dispersion and Current Observations by Dye, Drifter, and HF Radar in Coastal Water

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