Long Term Observations of Currents Over the Off Southern Bay of Bengal

The study was carried out in the southern Bay of Bengal (BoB) which located in east of Sri Lanka. The southern BOB is important for understanding water masses of the Bay of Bengal, Arabian Sea (AS) and equatorial Indian Ocean, interaction with currents. Previous studies revealed the entire BoB undergoes a dramatic seasonal variation in circulation patterns. The seasonally reversing north-south currents transport low-salinity water from the BoB into the AS while the overall flows are equatorward. The reversing monsoon currents pass adjacent to the south of Sri Lanka and transport water between the southern BoB and AS. Freshwater inputs, salinity-controlled mixed layers are important factors and have a strong influence in the flushing of the BoB. The field activities were carried out under Air-Sea Interaction in the Northern Indian Ocean (ASIRI) project in the BoB. The program included deployment of deep ocean (~4000 m) Acoustic Doppler Current Profiler (ADCP) mooring. The deployment was done in December 2013 and recovery was done in August 2015. The purpose was to understand and quantify currents, hydrography, mixing, and fresh and salty exchanges between the Southeast Arabian Sea and the Bay of Bengal which leading to give new insights into deep currents and small scale, high-frequency variability, some of which had not been observed ever before. Long-term time series of oceanographic data were collected from subsurface mooring in the southern Bay of Bengal. It was observed that some of the moorings were entangled with commercial fishing nets and lines, which leads top subsurface buoys ended up with unexpectedly closer to the surface than planned. The results indicated that near-surface currents as large as 1.75 m/s in July 2014. Currents stronger than 0.5 m/s were confined to the upper 250 m. Observations of oceanic currents, temperature, and sea surface height (SSH) revealed eddy like features formed with positive and negative SSH anomalies (~20 cm) moving westward at speeds of about 0.1 m/s. Further, results indicated the time period of the deployment, root-mean square velocity fluctuations were about 0.1 m/s near the surface but decayed with depth and became nearly uniform (~0.03–0.06 m/s) below 100 m.Keywords: Currents, Bay of Bengal, Eddies, Intra-seasonal oscillations, Sea surface height negative SSH anomalie

Presupernova Structure of Massive Stars

Issues concerning the structure and evolution of core collapse progenitor stars are discussed with an emphasis on interior evolution. We describe a program designed to investigate the transport and mixing processes associated with stellar turbulence, arguably the greatest source of uncertainty in progenitor structure, besides mass loss, at the time of core collapse. An effort to use precision observations of stellar parameters to constrain theoretical modeling is also described.Comment: Proceedings for invited talk at High Energy Density Laboratory Astrophysics conference, Caltech, March 2010. Special issue of Astrophysics and Space Science, submitted for peer review: 7 pages, 3 figure

Evolution of an isolated region in a stratified fluid

This paper reports an experimental study on the evolution of an isolated turbulent region in an otherwise quiescent linearly stratified fluid. A turbulent patch was generated by pulsed horizontal injection of a small volume of fluid. It was found that the turbulent blob thus produced initially grows as in a nonstratified fluid for a nondimensional time period of Nt ˜ 4 – 5 (with N the buoyancy frequency), attains a maximum height, and then physically collapses slowly to form a planar, quasi-two-dimensional dipole pattern. The timescale for the physical collapse of the blob was found to be much larger than that of the turbulence collapse. Scaling arguments are presented to explain the evolution of the turbulent region, and the experimental results are compared with the model predictions

The evolution of an isolated turbulent region in a two-layer fluid

A turbulent region is generated by horizontal pulsed injection at the interface of a two-layer fluid. Flow visualization studies reveal the existence of three stages in the evolution of the vertical size of this region: growth, maximum height, and collapse. A scaling analysis for the height of the turbulent region is presented, which appears to be in good agreement with the measurements. Comparable results were obtained by Fernando, van Heijst, and Fonseka (submitted to J. Fluid Mech.) for similar experiments in a linearly stratified fluid. Thorpe-scale measurements of the turbulent region reveal that the ratio of the rms displacement Lt and the maximum displacement Ltmax remain constant with time. The eventual formation process of the dipolar vortices after the collapse and the influence of interfacial wave motions on these dipolar vortices are discussed

Stratified Flow Past a Hill: Dividing Streamline Concept Revisited

The Sheppard formula (Q J R Meteorol Soc 82:528\u2013529, 1956) for the dividing streamline height Hs assumes a uniform velocity U 1e and a constant buoyancy frequency N for the approach flow towards a mountain of height h, and takes the form Hs/ h= (1 - F) , where F= U 1e/ Nh. We extend this solution to a logarithmic approach-velocity profile with constant N. An analytical solution is obtained for Hs/ h in terms of Lambert-W functions, which also suggests alternative scaling for Hs/ h. A \u2018modified\u2019 logarithmic velocity profile is proposed for stably stratified atmospheric boundary-layer flows. A field experiment designed to observe Hs is described, which utilized instrumentation from the spring field campaign of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program. Multiple releases of smoke at F 48 0.3 \u20130.4 support the new formulation, notwithstanding the limited success of experiments due to logistical constraints. No dividing streamline is discerned for F 48 10 , since, if present, it is too close to the foothill. Flow separation and vortex shedding is observed in this case. The proposed modified logarithmic profile is in reasonable agreement with experimental observations