Water characteristics, mixing and circulation in the Bay of Bengal during southwest monsoon

Influence of the freshwater influx, the wind forcing and the Indian Ocean monsoon drift current on the property distributions and the circulation in the Bay of Bengal during southwest monsoon has been quantified. At the head of the Bay, waters of low salinity, affected by the freshwater influx, occupy the upper 90 m water column. The isohaline 34.0 × 10−3 separating these waters from those of underlying saline waters shoals southward gradually and outcrops around 14N, 10N and 6N in the western, central and southeastern regions of the Bay respectively. The wind-stress-curl-induced upwelling effect is confined to depth limits of 50–100 m as is supported by a band of cold (24°–19°C) water in the central Bay. In the southern and central regions of the Bay, the monsoon drift current feeds the large scale cyclonic gyre apart from maintaining the northward flowing boundary current in the eastern Bay. A warm (27°–23°C), saline (35.0–35.2 × 10−3) watermass is advected northeastward along with the monsoon drift current into the Bay up to 14N at the depth limits of 50–100 m. Below this depth, in the western Bay a well-defined southward flow in the form of a boundary current is documented. Intense vertical mixing is inferred at the zones of salinity fronts in the depth limits of 40–100 m and also at deeper depths (\u3e 2200 m) and elsewhere lateral mixing is predominant

Observed changes in ocean acidity and carbon dioxide exchange in the coastal Bay of Bengal – a link to air pollution

Variations in surface water hydrographic properties and Dissolved Inorganic Carbon (DIC) were evaluated in the coastal Bay of Bengal using observations carried out during March–April 1991 and 2011, including 8 yr monthly time-series observations during 2005 and 2013. The coastal Bay of Bengal is characterised by relatively fresher, more basic and lower pCO2 in 1991 compared to 2011. The rates of decrease in pH, increase in DIC and pCO2 per decade were consistent with global trends in the Southwestern (SW) coastal Bay of Bengal, whereas rates in the Northwestern (NW) coastal Bay of Bengal were observed to be 3–5 times higher. The associated recent increase in sulphate and nitrogen aerosol loadings over NW Bay of Bengal from the Indo-Gangetic Plain and Southeast Asia during winter and spring may be mainly responsible for the increased acidity in recent years. Thus, this region, which was previously considered to be a significant sink for atmospheric CO2, now seems to have become a source of CO2 to the atmosphere

Temperature dependence of photo-elastic constants in alkali halides

The paper furnishes measurements on the birefringence produced at different temperatures in crystals of NaCl, KCl and KBr when subjected to stress. The results show that the stress-optical coefficients (q 11 -q 12) and q 44 decrease in the case of NaCl almost linearly with temperature while in KCl and KBr they increase with the same. The variation for rock salt is of the order of about 30% over an interval of 300° C. In both KCl and KBr, the variation in (q 11 -q 12) which is about 40% over the same interval of temperature is much greater than inq 44 which is of the order of about 15%. The corresponding strain-optical coefficients are also evaluated and given at each temperature

Temperature dependence of photo-elastic constants in plastics

This article does not have an abstract

Model simulation of tide-induced currents in Gauthami-Godavari estuary

Predictive spatial distribution of flow field has been simulated from the time series data on currents and tides during dry season (11-19, February, 2009) in the Gauthami-Godavari Estuary utilizing TIDAL model. A 2D-Tidal Estuarine model has been considered (instead of 3D model) due to well-mixed type system and its circulation is dominated by tides during the observational period. The model forcing functions consist of wind and tidal elevations along the open boundaries and no fresh water inflow from the main stream and no land flood in river system. The bathymetry data of the river basin has been collected and supplemented to the model as one of the rigid boundary conditions to evaluate integration. The bottom roughness length (K) was adjusted to achieve model calibration and verification in model simulations of flow field. The model simulation results are in qualitative agreement with the observational data with calibrated bottom roughness length which is about 0.085 m. Model results reveal that the majority of flow was found to be along the channel axis (i.e. high iso-bath contour). During flood time, flow is south-west direction and it is changed to northeast direction during ebb period which is indicating that the model results resemble flow in the real eastern system

Metamorphosis of helical magnetorotational instability in the presence of axial electric current

This paper presents numerical linear stability analysis of a cylindrical Taylor-Couette flow of liquid metal carrying axial electric current in a generally helical external magnetic field. Axially symmetric disturbances are considered in the inductionless approximation corresponding to zero magnetic Prandtl number. Axial symmetry allows us to reveal an entirely new electromagnetic instability. First, we show that the electric current passing through the liquid can extend the range of helical magnetorotational instability (HMRI) indefinitely by transforming it into a purely electromagnetic instability. Two different electromagnetic instability mechanisms are identified. The first is an internal pinch-type instability, which is due to the interaction of the electric current with its own magnetic field. Axisymmetric mode of this instability requires a free-space component of the azimuthal magnetic field. When the azimuthal component of the magnetic field is purely rotational and the axial component is nonzero, a new kind of electromagnetic instability emerges. The latter driven by the interaction of electric current with a weak collinear magnetic field in a quiescent fluid gives rise to a steady meridional circulation coupled with azimuthal rotation.Comment: 10 pages, 12 figures, final versio

Effect of intensive melt shearing on the formation of Fe-containing intermetallics in LM24 Al-alloy

Fe is one of the inevitable and detrimental impurities in aluminium alloys that degrade the mechanical performance of castings. In the present work, intensive melt shearing has been demonstrated to modify the morphology of Fe-containing intermetallic compounds by promoting the formation of compact α-Al(Fe,Mn)Si at the expense of needle-shaped β-AlFeSi, leading to an improved mechanical properties of LM24 alloy processed by MC-HPDC process. The promotion of the formation of α -Al(Fe, Mn)Si phase is resulted from the enhanced nucleation on the well dispersed MgAl 2O 4 particles in the melt. The Fe tolerance of LM24 alloy can be effectively improved by combining Mn alloying and intensive melt shearing

Stock assessment of silverbellies of India with particular reference to Andhra Pradesh and Tamil Nadu

Along Indian coasts, the silveifoellies are exploited by trawl and aitisanal gears but bulk of the landings are obtained by tiawlt which operate up to SO m depth. During 1979-83, the estimated annual average silvetbelly landings were 69 000 tonnes, whereas during 1984-88 these were 62 000 tonnes. Maximum silveibelly landings were obtained in Tamil Nadu which contributed 70.5% ol total all-India silverbelly landings followed by Andhra Pradesh (9%), Kerala (8.4%), Kamataka (6%) and other sutes (6.1%). Out of 20 species of silveibellies, known to occur in the seas around India, LeiogiuUhus bindus and Secutor insidiator were most dominant along Andhra Pradesh and northern Tamil Nadu coasts, together contributing to 64% and SS% respectively of tilveibeUy landings. Along southern Tamil Nadu, L. joiusi and L. dussumeri were most dominant together forming about 60% of silvetbelly catch in the region

Variability in stratification and flushing times of the Gautami–Godavari estuary, India

In order to examine the influence of forcing (river flow and tides) and anthropogenic activities (dredging and dam regulation) on stratification, a study was conducted over a period of 19 months (June 2008–December 2009) in the Gautami–Godavari estuary (G–GE) during spring and neap tide periods covering entire spectrum of discharge over a distance of 36 km from the mouth. The bathymetry of the estuary was recently changed due to dredging of ∼20 km of the estuary from the mouth for transportation of barges. This significantly changed the mean depth and salinity of the estuary from its earlier state. The variations in the distribution of salinity in the Godavari estuary are driven by river discharge during wet period (June–November) and tides during dry period (December–May). The weak stratification was observed during high discharge (July–August) and no discharge (January–June) periods associated with dominant fresh water and marine water respectively. The strong stratification was developed associated with decrease in discharge during moderate discharge period (October–December). Relatively stronger stratification was noticed during neap than spring tides. The 15 psu isohaline was observed to have migrated ∼2–3 km more towards upper estuary during spring than neap tide suggesting more salt enters during former than latter period. Total salt content was inversely correlated with river discharge and higher salt of about 400×106 m3 psu was observed during spring than neap tide. Flushing times varied between less than a day and more than a month during peak and no discharge periods respectively with lower times during spring than neap tide. The flushing times are controlled by river discharge during high discharge period, tides during dry period and both (river discharge and tides) under moderate discharge period. This study suggests that modification of discharge, either natural due to weak monsoon or artificial such as dam constructions and re-routing the river flow, may have significant impact on the stratification and biogeochemistry of the Godavari estuary

Observation of coherent backscattering of light by cold atoms

Coherent backscattering (CBS) of light waves by a random medium is a signature of interference effects in multiple scattering. This effect has been studied in many systems ranging from white paint to biological tissues. Recently, we have observed CBS from a sample of laser-cooled atoms, a scattering medium with interesting new properties. In this paper we discuss various effects, which have to be taken into account for a quantitative study of coherent backscattering of light by cold atoms.Comment: 25 pages LaTex2e, 17 figures, submitted to J. Opt. B: Quant. Semicl. Op