| 1. |
- Dey, Dipanjan, et al.
(författare)
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An assessment of TropFlux and NCEP air-sea fluxes on ROMS simulations over the Bay of Bengal region
- 2017
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Ingår i: Dynamics of atmospheres and oceans (Print). - : Elsevier BV. - 0377-0265 .- 1872-6879. ; 80, s. 47-61
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Tidskriftsartikel (refereegranskat)abstract
- This study presents an assessment of the TropFlux and the National Centers for Environmental Prediction (NCEP) reanalysis air-sea fluxes in simulating the surface and subsurface oceanic parameters over the Bay of Bengal (BoB) region during 2002-2014 using the Regional Ocean Modelling System (ROMS). The assessment has been made by comparing the simulated fields with in-situ and satellite observations. The simulated surface and subsurface temperatures in the TropFlux forced experiment (TropFlux-E) show better agreement with the Research Moored Array for African-Asian-Australian Monsoon Analysis (RAMA) and Argo observations than the NCEP forced experiment (NCEP-E). The BoB domain averaged sea surface temperature (SST) simulated in the NCEP-E is consistently cooler than the satellite SST, with a root mean square error (RMSE) of 0.79 C. Moreover, NCEP-E shows a limitation in simulating the observed seasonal cycle of the SST due to substantial underestimation of the pre-monsoon SST peak. These limitations are mostly due to the lower values of the NCEP net hedt flux. The seasonal and interannual variations of SST in the TropFlux-E are better comparable to the observations with correlations and skills more than 0.80 and 0.90 respectively. However, SST is overestimated during summer monsoon periods mainly due to higher net heat flux. The superiority of TropFlux forcing over the NCEP reanalysis can also.be seen when simulating the interannual variabilities of the magnitude and vertical extent of Wyrtki jets at two equatorial RAMA buoy locations. The jet is weaker in the NCEP-E relative to the TropFlux-E and observations. The simulated sea surface height anomalies (SSHA) from both the experiments are able to capture the regions of positive and negative SSHA with respect to satellite-derived altimeter data with better performance in the TropFlux-E. The speed of the westward propagating Rossby wave along 18 N in the TropFlux-E is found to be about 4.7 cm/s, which is close to the theoretical phase speed of Rossby waves.
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| 2. |
- Mandal, Samiran, et al.
(författare)
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Characteristics and evolution of a coastal mesoscale eddy in the Western Bay of Bengal monitored by high-frequency radars
- 2019
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Ingår i: Dynamics of atmospheres and oceans (Print). - : Elsevier BV. - 0377-0265 .- 1872-6879. ; 88
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Tidskriftsartikel (refereegranskat)abstract
- Evolution of a coastal cyclonic eddy has been investigated using surface current observations from high-frequency radar (HFR) along the western Bay of Bengal (BoB) near Andhra Pradesh coast during October-December 2015. The HFRS tracked the genesis of the cyclonic eddy from early October, which persisted throughout November and dissipated after mid-December within the shelf-slope regions of HFR domain along the western boundary of BoB. A vector-based technique has been adapted to detect and track the mesoscale cyclonic eddy. The eddy is observed to propagate with a mean speed of similar to 0.27m s(-1) (23.36 km day(-1)). It is asymmetric in nature with an average radius of similar to 90 (80) km along the eastern and western (northern and southern) sides of the cyclonic eddy aligned along-shelf. The eddy has been characterized based on the Eulerian parameters; normalized vorticity (similar to 0.75), divergence (similar to 0.20), strain (similar to 0.25), and Okubu-Weiss (OW) parameter (-0.7 x 10(-9)s(-2)). Positive vorticity and divergence, along with lower strain at the eddy center, justify the cyclonic eddy. The negative values of OW parameter show good agreement with the eddy-cores detected. Kinematics show that the Rossby number (R-0) varies in the range 0.6-1.2, depicting that the cyclonic eddy is associated with mesoscale dynamical features and matches perfectly with the geostrophic balance. The eddyinduced upwelling signatures are observed from the subsurface temperature and salinity structures. The upwelling is well supported by positive (similar to 11 x 10(-7) N m(-3)) wind stress curl during November. The sea surface temperature (SST), surface chlorophyll-alpha concentration as well as sea surface salinity (SSS) associated with the cyclonic eddy, show the advection of warm waters from the open ocean and low saline cold waters from the coastline. This study reveals that the eddy evolved due to baroclinic instability, well indicated by positive values of T2 (rate of conversion of mean potential energy to eddy potential energy) and lower values of Brunt-Vaisala Frequency (N-2), whereas growth and intensification of the eddy are attributed to barotropic instability, supported by the positive values of T4 (the conversion of mean kinetic energy to eddy kinetic energy).
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| 3. |
- Pramanik, Saikat, et al.
(författare)
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Role of interannual equatorial forcing on the subsurface temperature dipole in the Bay of Bengal during IOD and ENSO events
- 2019
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Ingår i: Ocean Dynamics. - : Springer Science and Business Media LLC. - 1616-7341 .- 1616-7228. ; 69:11-12, s. 1253-1271
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Tidskriftsartikel (refereegranskat)abstract
- Role of equatorial forcing on the thermocline variability in the Bay of Bengal (BoB) during positive and negative phases of the Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO) was investigated using the Regional Ocean Modeling System (ROMS) simulations during 1988 to 2015. Two numerical experiments were carried out for (i) the Indian Ocean Model (IOM) with interannual open boundary conditions and (ii) the BoB Model (BoBM) with climatological boundary conditions. The first mode of Sea Surface Height Anomalies (SSHA) variability showed a west-east dipole nature in both IOM and altimetry observations around 11 degrees N, which was absent in the BoBM. The vertical section of temperature along the same latitude showed a sharp subsurface temperature dipole with a core at similar to 100 m depth. The positive (negative) subsurface temperature anomalies were observed over the whole northeastern BoB during NIOD (PIOD) and LN (EN) composites due to stronger (weaker) second downwelling Kelvin Waves. During the negative phases of IOD and ENSO, the cyclonic eddy on the southwestern BoB strengthened due to intensified southward coastal current along the western BoB and local wind stress. The subsurface temperature dipole was at its peak during October-December (OND) with 1-month lag from IOD and was evident from the Argo observations and other reanalysis datasets as well. A new BoB dipole index (BDI) was defined as the normalized difference of 100-m temperature anomaly and found to be closely related to the frequency of cyclones and the surface chlorophyll-a concentration in the BoB.
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