J. Srinivasan

Enhanced aerosol loading over Arabian Sea during the pre-monsoon season: Natural or anthropogenic?

[1]xa0Recent experiments conducted over the oceanic regions adjacent to the Indian sub continent have revealed the presence of anthropogenic aerosol haze during January to March. It has been suggested that the major source of this aerosol is South and Southeast Asia. Here we show from long term, multi-station and ship borne observations that aerosols transported from regions northwest of Indian subcontinent especially Arabian and Saharan regions (mostly natural dust) along with the locally produced sea-salt aerosols by sea-surface winds constitute a more significant source of aerosols during April–May period. The radiative forcing due to Arabian/Saharan aerosols (mostly natural) during April–May period is comparable and often exceed (as much as 1.5 times) the forcing due to anthropogenic aerosols during January to March period. The presence of dust load over the Arabian Sea can influence the temperature profile and radiative balance in this region.

Numerical study of steady-state laser melting problem

Abstract A two-dimensional steady-state laser melting problem is numerically simulated. A vorticitystream function formulation is used to solve momentum equations and a method of selecting the optimum relaxation parameter is suggested. Steady-state finite-difference equations are solved by an alternative direction implicit (ADI) scheme using a false transient formulation. A solid and liquid interface is approximated by steps. The role of surface tension driven flow on total heat transfer is studied. Comparative studies are carried out between conduction and convection results. The flow pattern in the molten pool is presented through stream function plots which show the effect of laser power on the size and strength of secondary cells. The effect of a secondary cell on the total heat transfer and pool shape is analysed under varying laser power.

A numerical study of thermocapillary flow in a rectangular cavity during laser melting

The surface tension gradient driven flow that occurs during laser melting has been studied. The vorticity-streamfunction form of the Navier-Stokes equations and the energy equation has been solved by the ‘Alternative Direction Implicit’ method. It has been shown that the inertia forces in the melt strongly influence the flow pattern in the melt. The convection in the melt modifies the isotherms in the melt at high surface tension Reynolds number and high Prandtl number. The buoyancy driven flow has been shown to be negligible compared to the surface tension gradient driven flow in laser melting.

Low frequency variation of tropical convergence zones

SummaryIntraseasonal variation of tropical convergence zones (TCZ) is studied focussing on the three major features of the TCZ over the Indian longitudes during the summer monsoon viz. (i) the oscillation between active and weak spells, (ii) the occurrence of two favourable zones — one over the equatorial oceans and another over the heated continent and (iii) poleward propagations of the oceanic TCZ onto the heated continent. An observational study of the intraseasonal variation over different parts of the tropics has shown that the first feature may be an ubiquitous feature of the TCZ variations, the second occurs only over the Asian summer and winter monsoon zones, and the third only over the Asian summer monsoon. Analysis of a simple monsoon model has revealed that poleward propagation occurs in the presence of a meridional surface temperature gradient because the convective heating is asymmetric, with more heating on the poleward side. Preliminary analysis of the T-21 version of the ECMWF model has shown that it is capable of simulating the three major features of the intraseasonal variation of the TCZ over the Indian longitudes during the summer monsoon.

Numerical study of double-diffusive free convection from a vertical surface

The double-diffusive free convective flow from a vertical surface has been studied numerically. The mass, momentum, energy and species conservation equations have been solved by a inite-difference method using an explicit scheme. Boundary layer and Boussinesq approximations have been incorporated. The velocity, temperature and concentration profiles indicate complex interaction between temperature and concentration driven buoyancy flows. The effects of Schmidt number and buoyancy ratio on the temperature profile have been discussed. The role of temperature stratification in the ambient has been highlighted.

Natural Convection Flows Due to the Combined Buoyancy of Heat and Mass Diffusion in a Thermally Stratified Medium

This paper presents a numerical study of laminar doubly diffusive free convection flows adjacent to a vertical surface in a stable thermally stratified medium. The two buoyant mechanisms are thermal diffusion and species diffusion. The species concentration is assumed to be small. Boussinesq approximations are incorporated and the governing conservation equations of mass, momentum, energy, and species are nondimensionalized. These equations are solved using a finite-difference method. The results are explained in terms of the basic physical mechanisms that govern these flows. It is observed that the ambient thermal stratification has a profound influence on the transport characteristics. The results show many interesting aspects of the complex interaction of the two buoyant mechanisms.

Bifurcation in a buoyant horizontal laminar jet

The trajectory of a laminar buoyant jet discharged horizontally has been studied. The experimental observations were based on the injection of pure water into a brine solution. Under certain conditions the jet has been found to undergo bifurcation. The bifurcation of the jet occurs in a limited domain of Grashof number and Reynolds number. The regions in which the bifurcation occurs has been mapped in the Reynolds number-Grashof number plane. There are three regions where bifurcation does not occur. The various mechanisms that prevent bifurcation have been proposed.

Meridional Migration of Tropical Convergence Zones

Abstract Outgoing longwave radiation data from the Earth Radiation Budget Experiment show that the meridional migration of tropical convergence zones (TCZ) varies greatly from one region to another in the Tropics. In Africa, the meridional migration of TCZ is limited due to the meridional variation of the planetary net radiation due to the Sahara Desert. The large meridional migration in the Asian subcontinent and the west Pacific Ocean is attributed to the strong land-sea contrast in these regions. The wind-evaporation feedback mechanism is proposed as the cause of intraseasonal meridional migration of TCZ in the Atlantic and east Pacific Oceans.

The role of heat fluxes and moist static energy in tropical convergence zones

The relationship between monthly mean outgoing longwave radiation (OLR) and the mean moist static energy of the lower troposphere is shown to be similar to the relationship between monthly mean OLR and sea surface temperature over the oceanic regions. The relationship between monthly mean OLR and surface moist static energy shows that the threshold value for the onset of convection is different in continental and oceanic regions. However, the threshold of moist static stability for the troposphere (surface to 400 mb) is the same for oceans and continents. This relationship is consistent with the simple model of the tropical convergence zones proposed by Neelin and Held. The net energy convergence in the troposphere was found to be positive in regions with OLR below 210 W

Criteria for acoustic instability in a gas with ambient vibrational and radiative nonequilibrium

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