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>

scholarly journals Wind-Driven Ageostrophic Transport in the North Equatorial Countercurrent of the Eastern Pacific at 95°W

2009 ◽  
Vol 39 (11) ◽  
pp. 2985-2998 ◽  
Author(s):  
Janet Sprintall ◽  
Sean Kennan ◽  
Yoo Yin Kim ◽  
Peter Niiler
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Ekman Transport ◽  
Momentum Balance ◽  
Altimeter Data ◽  
Turbulent Stress ◽  
Wind Stress Curl ◽  
Turbulent Layer ◽  
Near Surface ◽  
The North

Abstract Observations of horizontal velocity from two shipboard acoustic Doppler current profilers (ADCPs), as well as wind, temperature, and salinity observations from a cruise during June–July 2001, are used to compute a simplified mean meridional momentum balance of the North Equatorial Countercurrent (NECC) at 95°W. The terms that are retained in the momentum balance and derived using the measurements are the Coriolis and pressure gradient forces, and the vertical divergence of the turbulent stress. All terms were vertically integrated over the surface turbulent layer. The K-profile parameterization (KPP) prescribed Richardson number (Ri) is used to determine the depth of the turbulent boundary layer h at which the turbulent stress and its gradient vanish. At the time of the cruise, surface drifters and altimeter data show the flow structure of the NECC was complicated by the presence of tropical instability waves to the south and a strong Costa Rica Dome to the north. Nonetheless, a consistent, simplified momentum balance for the surface layer was achieved from the time mean of 19 days of repeat transects along 95°W with a 0.5° latitude resolution. The best agreement between the ageostrophic transport determined from the near-surface cruise measurements and the wind-derived Ekman transport was obtained for an Ri of 0.23 ± 0.05. The corresponding h ranges from ∼55 m at 4°N to ∼30 m within the NECC core (4.5°–6°N) and shoaling to just 15 m at 7°N. In general, the mean ageostrophic and Ekman transports decreased from south to north along the 95°W transect, although within the core of the NECC both transports were relatively strong and steady. This study underscores the importance of the southerly wind-driven eastward Ekman transport in the turbulent boundary layer before the NECC becomes fully developed later in the year through indirect forcing from the wind stress curl.

scholarly journals Meteorological Regimes of the Most Intense Convective Systems along the Southern Himalayan Front

2016 ◽  
Vol 29 (12) ◽  
pp. 4383-4398 ◽  
Author(s):  
Xueke Wu ◽  
Xiushu Qie ◽  
Tie Yuan ◽  
Jinliang Li
Keyword(s):  
Summer Monsoon ◽  
Bay Of Bengal ◽  
Convective Available Potential Energy ◽  
Principal Component ◽  
Specific Humidity ◽  
Multivariate Techniques ◽  
Near Surface ◽  
Convective Systems ◽  
Southwesterly Wind ◽  
Transport Passage

Abstract Based on 16 years of Tropical Rainfall Measuring Mission (TRMM) data and NCEP Climate Forecast System Reanalysis data, the most intense convective systems (ICSs) along the southern Himalayan front (SHF) are studied using the multivariate techniques of principal component analysis in T mode and k-means cluster analysis. Three clusters, classified according to the near-surface fields of wind, specific humidity, convective available potential energy, and convective inhibition, correspond to the premonsoon (March–May), the establishment of the monsoon (late May–early June), and the Indian summer monsoon itself (June–September), respectively. The location of ICSs along the SHF is closely related to the establishment of the transport passage from the eastern SHF to the northwestern SHF along the Himalayas. During the premonsoon, the southwesterly wind is weak and moist air from the Bay of Bengal is transported to the eastern SHF, where ICSs are densely distributed. The oceanic southwesterly wind is enhanced and the transport passage extends to the central SHF during the monsoon establishment period, when ICSs distribute over the whole SHF homogeneously. The southwesterly wind is the strongest and the transport passage extends to the westernmost SHF after the monsoon is established, when ICSs mainly concentrate over the concave indentation region. Backward trajectory analysis confirms that, besides the local environment, the moisture transport from the Arabian Sea (17%) and the Bay of Bengal (9%) are two important long-range transport pathways for the summer monsoon ICSs at the western end of the SHF.

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 Seasonal SSH Variability of the Northern South China Sea

2015 ◽  
Vol 45 (6) ◽  
pp. 1595-1609 ◽  
Author(s):  
Fang-Hua Xu ◽  
Lie-Yauw Oey
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific Ocean ◽  
Northern South China Sea ◽  
Luzon Strait ◽  
Height Anomaly ◽  
Ekman Pumping ◽  
Wind Stress Curl ◽  
China Sea ◽  
The North

AbstractThe seasonal response of sea surface height anomaly (SSHA) to wind stress curl (WSC) in the northern South China Sea (NSCS) and the Kuroshio intrusion through the Luzon Strait is analyzed using observations and models. The dominant response to WSC is through simple Ekman pumping, while effects of β appear as the weaker second empirical orthogonal function mode. The Luzon Strait intrusion is shown to be largely deterministic using a model forced by realistic wind in the North Pacific Ocean, and it contributes significantly to the SSH variability in the NSCS. The WSC accounts for 62%, while intrusion 38% of the total forcing, but the latter alters the forced Rossby wave response. Without the intrusion, westward propagation is too fast, resulting in incorrect balance and erroneous annual SSH variability in the NSCS.

scholarly journals Near-surface salinity and stratification in the north Bay of Bengal from moored observations

2016 ◽  
Vol 43 (9) ◽  
pp. 4448-4456 ◽  
Author(s):  
Debasis Sengupta ◽  
G. N. Bharath Raj ◽  
M. Ravichandran ◽  
J. Sree Lekha ◽  
Fabrice Papa
Keyword(s):  
Bay Of Bengal ◽  
Surface Salinity ◽  
Near Surface ◽  
The North
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