Thermal-convective instability of a composite rotating stellar atmosphere in the presence of a variable magnetic field,medium permeability and solute gradient

The thermal-convective instability of a composite rotating stellar atmosphere in the presence of a variable horizontal magnetic field is considered to include, separately, the effects of medium permeability and solute gradient. The criteria for monotonic instability in each case have been obtained which generalize the Defouw's criterion derived for thermal-convective instability in the absence of above effects.     

List of forthcoming papers

List of forthcoming papers     

Thermosolutal-convective instability of a composite stellar atmosphere in the presence of a variable magnetic field

The thermosolutal-convective instability of a composite stellar atmosphere is considered in the presence of variable horizontal magnetic field and collisional effects. The criteria for monotonic instability are obtained which generalize the criterion derived for thermal-convective instability in the absence of above effects.     

Gravitational instability of a composite and rotating plasma in the presence of a variable magnetic field through a porous medium

The gravitational instability of an infinite homogeneous self-gravitating plasma through porous medium is considered to include, separately, the effects due to rotation and collisions between ionized and neutral components. The dispersion relations are obtained in both cases. It is found that the gravitational instability of a composite and rotating plasma in the presence of a variable horizontal magnetic field through porous medium is determined by the Jeans's criterion.     

A spatially explicit modeling approach to explore scenarios of sustainable agriculture futures

The transition to agricultural sustainability involves difficult choices and an understanding of the complex trade-offs associated with agricultural activities. Decision support tools and techniques assist in making the informed decisions for a transition to sustainable agriculture. Georgia Basin — Quite Useful Ecosystem Scenario Tool (GB-QUEST) is a computer-based, user-friendly tool that has been developed to look at the future sustainability scenarios of the Georgia Basin in British Columbia. The objective of this paper is to describe the agricultural model that has been developed for implementation in GB-QUEST. We present its framework, spatial methodology for land-use simulation, and the initial results of its application. The agriculture model is a spatial model that examines the social, economic and environmental consequences of user-defined agricultural development strategies. The model simulates changes in the Georgia Basin from the year 2000 to 2040 in decadal steps. User choices of local and global development factors, along with their "worldview" choices, are important inputs in the model that determine the effects on environmental and socio-economic systems. The model has two components — Generation of land-use scenarios, and Development of Indicator models. The first component uses cell-based spatial algorithms to simulate likely changes/conversions in land-use up to the year 2040. The approach used here integrates the functionality of Multi-Criteria Evaluation (MCE) and Cellular Automata (CA) techniques in order to simulate the land-use conversions. It uses Geographic Information Systems (GIS) and remote sensing techniques for creating, storing and deriving the data sets required for the model. The second component develops the indicator models for relating scenario variables to socio-economic and environmental variables such as physical and economic yields, economic operation costs and nutrient surplus per unit area. These indicator models are used to evaluate land-use scenarios generated by the users. The model encourages understanding of sustainability, by allowing one to explore different possible scenarios of the future for their environmental and socio-economic consequences.     

Remote sensing of spectral signatures of tropospheric aerosols

With the launch of the German Aerospace Agency's (DLR) Modular Opto-electronic Scanner (MOS) sensor on board the Indian Remote Sensing satellite (IRS-P3) launched by the Indian Space Research Organization (ISRO) in March 1996, 13 channel multi-spectral data in the range of 408 to 1010 nm at high radiometric resolution, precision, and with narrow spectral bands have been available for a variety of land, atmospheric and oceanic studies. We found that these data are best for validation of radiative transfer model and the corresponding code developed by one of the authors at Space Applications Centre, and called ATMRAD (abbreviated for ATMospheric RADiation). Once this model/code is validated, it can be used for retrieving information on tropospheric aerosols over ocean or land. This paper deals with two clear objectives, viz.,

Alfvénic drift Kelvin-Helmholtz instability in the presence of an equilibrium electric field

Alfvénic drift Kelvin-Helmholtz instability is discussed in the presence of equilibrium electric and magnetic fields which are perpendicular to each other. A dispersion relation is achieved with the help of WKB approximation and the instability criterion is established. A comparison is made with the previous studies and it is shown that the electric field has a stabilizing or destabilizing effect on the system according to the conditions discussed in the text.     

Spatio-temporal fluctuations in HeI 10830 Å line parameters: Evidence for spicule formation

The equivalent width, line depth, line width, and Doppler shift of the He i 10830 Å line were extracted from two time series of spectra. Scatter plots of time-averaged line depth, line width, and Doppler shifts, as well as the root mean square temporal fluctuation of these quantities against the time-averaged equivalent width at a few hundred spatial locations were obtained. The statistical behaviour of these line parameters and their fluctuations was used to infer plausible reasons for the fluctuations. Examination of these results showed that the line parameter fluctuations could be caused by fluctuations in the coronal UV radiation (which could drive the spicules) or by the appearance of density inhomogeneities such as spicules within the line forming domain. In either case, the data can be interpreted as representing the initial phases of spicules.     

Study of calcium-K network evolution from Antarctica

To study the evolution of large convective cells known as supergranules, a solar telescope was set up at Maitri, Indian permanent station in Antarctica region, during the local summer months (December 1989 through March 1990). A continuous sequence of calcium K-line filtergrams for 106 hours spaced at intervals of about 10 min was obtained. The analysis of the data indicates that the most probable lifetime of the calcium-K network is about 22 hours. The lifetime depends upon the size of the cell and is larger for bigger cells. The data also show that cells (of a given size) associated with remnant magnetic field regions live longer than those in the field-free region. This may mean that the magnetic field plays an important role in the confinement of these structures.