Cosmological models in generalized scalar-tensor theory with cosmological term and bulk viscosity

Exponential and power law solutions for homogeneous cosmological modelshave been discussed in a generalized scalar-tensor theory where both thecosmological term and coupling parameter are taken tobe functions of the scalar field , along with the bulk viscousstress of the cosmic fluid. Assuming simple relationships of the scalarfield with the cosmological term and the coupling parameter, all thesolutions are studied in Dicke's revised units. By use of a conformaltransformation, the solutions are also expressed in atomic units.     

Early cosmological models in Lyra's geometry

A spatially homogeneous and isotropic Robertson-Walker model withzero-curvature of the universe is studied within the frame-work of Lyra'smanifold. The gauge-function in Lyra's manifold is taken to betime-dependent. Exact solutions of Einstein equations are obtained for twodifferent early phases of the universe viz. Inflationary phase andradiation-dominated phase by using `gamma-law' equation of statep = ( - 1) . The -index, describing the material content,varies continuously with cosmic time so that in the course of itsevolution, the universe goes through a transition from an inflationaryphase to a radiation-dominated phase. The physical properties of themodels are also discussed.     

Impact of surface meteorological observations on RAMS forecast of monsoon weather systems over the Indian region

Summary An attempt has been made to study the impact of surface meteorological observations on the Regional Atmospheric Modelling System (RAMS) simulation of a monsoon depression and two low pressure systems. The surface observations are blended with the GEWEX Asian Monsoon Experiment (GAME) gridded analyses for these cases. In one set of experiments the model is run in 12 hour nudging mode initially and then in forecast mode using GAME gridded data without incorporating surface observations. In another set of experiments surface data are incorporated to enhance the signature of the systems in the large scale GAME analyses and nudging is applied initially for twelve hours. Subsequently the model is run in forecast mode to see the temporal and spatial evolution of different meteorological features associated with the systems. It is found that inclusion of the surface data has in general enhanced the signature of the systems in the analysis and subsequently shows improvement in the forecast of sea-level pressure, geopotential, wind field, etc. and the associated forecast of heavy rainfall, in particular. To make a quantitative comparison of the predicted rainfall with the observed one, equitable threat score and bias are calculated for different threshold values of rainfall. It is clearly noted that inclusion of surface data has improved the precipitation forecast over the Indian land mass as indicated by the equitable threat score and bias for all the threshold rainfall categories.     

Response of the Indian summer monsoon circulation and rainfall to seasonal snow depth anomaly over Eurasia

Several observational and modeling studies indicate that the Indian summer monsoon rainfall (ISMR) is inversely related to the Eurasian snow extent and depth. The other two important surface boundary conditions which influence the ISMR are the Pacific sea surface temperature (SST) to a large extent and the Indian Ocean SST to some extent. In the present study, observed Soviet snow depth data and Indian rainfall data for the period 1951–1994 have been statistically analyzed and results show that 57% of heavy snow events and 24% of light snow events over west Eurasia are followed by deficient and excess ISMR respectively. Out of all the extreme monsoon years, care has been taken to identify those when Eurasian snow was the most dominant surface forcing to influence ISMR. During the years of high(low) Eurasian snow amounts in spring/winter followed by deficient(excess) ISMR, atmospheric fields such as temperature, wind, geopotential height, velocity potential and stream function based on NCEP/NCAR reanalyses have been examined in detail to study the influence of Eurasian snow on the midlatitude circulation regime and hence on the monsoon circulation. Results show that because of the west Eurasian snow anomalies, the midlatitude circulations in winter through spring show significant changes in the upper and lower level wind, geopotential height, velocity potential and stream function fields. Such changes in the large-scale circulation pattern may be interpreted as precursors to weak/strong monsoon circulation and deficient/excess ISMR. The upper level velocity potential difference fields between the high and low snow years indicate that with the advent of spring, the winter anomalous convergence over the Indian region gradually becomes weaker and gives way to anomalous divergence that persists through the summer monsoon season. Also the upper level anomalous divergence centre shifts from over the Northern Hemisphere and equator to the Southern Hemisphere over the Indian Ocean and Australia.     

Adaptation in Canadian Agriculture to Climatic Variability and Change

The effects of climatic variability and change on Canadian agriculture have become an important research field since the early 1980s. In this paper, we seek to synthesize this research, focusing on agricultural adaptation, a purposeful proactive or reactive response to changes associated with climate, and influenced by many factors. A distinctive feature of methods used in research on adaptation in Canadian agriculture is the focus on the important role of human agency. Many individual farmers perceive they are well adapted to climate, because of their extensive 'technological' tool-kit, giving them confidence in dealing with climatic change. In many regions, little concern is expressed over climatic change, except where there are particular types of climatic vulnerability. Farmers respond to biophysical factors, including climate, as they interact with a complex of human factors. Several of these, notably institutional and political ones, have tended to diminish the farm-level risks stemming from climatic variability and change, but may well increase the long term vulnerability of Canadian agriculture. Notwithstanding the technological and management adaptation measures available to producers, Canadian agriculture remains vulnerable to climatic variability and to climate change.     

Vertical Variation of Madden-Jullian Oscillations in the Normal Monsoon Season as Revealed Through MST Radar Wind Data

Summary  Mesosphere-Stratosphere-Troposphere (MST) Radar wind data for the period June through September 1996 have been examined to study vertical variation of Madden-Jullian Oscillations in wind and eddy kinetic energy (eke) in the normal monsoon season. The domain of analysis in the vertical is from 6 to 20 km with a height resolution of 150 m. Fast-Fourier-Transformation (FFT) has been applied to zonal (u), meridional(v) components of wind to extract the Madden-Jullian oscillations and eke. There are three dominant modes viz., 50–70, 30–40 and 10–20 day periodicity, which contain considerable fraction of energy and show high degree of vertical variability. The peak amplitude of 50–70 day mode in u, 30–40 mode in v and eke were observed at 16–17 km just below the tropopause level. The peak amplitudes of 30–40 day mode in u and 50–70 day mode in v were found in the height region of 13–16 km. To understand the origin and propagation of these waves, wave energy is calculated. The wave energy is higher at tropospheric heights than at lower stratospheric heights indicating that the origin of these waves is in the troposphere, and a part of the energy leaks into the stratosphere. Received September 17, 1998/Revised September 26, 1999     

Loktak notified Wetland ecosystem and its catchment

Conservation of wetland is considered paramount in view of its ecological significance. The availability of reliable and up-to-date data on seasonal water spread, tropic state of wetland and bio-physical parameters besides the landuse/cover of the catchment area is a prerequisite for ‘wise use’ of any wetland ecosystem. The present study is carried out to identify the above parameters of Loktak notified wetland through visual interpretation of 1RS IA/IB LISS II FCC of 1990 and 1994/95. It indicates that the water spread of the lake is showing a declining trend and an increasing trend for aquatic vegetation. In 1990 post-monsoon data water spread was 15441 ha which become 11166 ha in October 1994. The extent of water spread further decreases by pre-monsoon season and was found to be 7875 ha in the IRS LISS II data of March 1995. Like-wise area under aquatic vegetation and associated marshy/ swamps was 10499 ha in October 1990 and 13506 ha in October 1994. Catchment of Loktak lake (104872 ha) is highly degraded and forest covers only 7205 ha area. Agriculture is the main land use (35576 ha) in the catchment and substantial area is also under land with or without scrub. Thus, there is a need to rehabilitate the catchment by way of planting trees for reducing silt load in the Loktak lake and ensuring its ‘wise use’.     

Identification of flood seasonality and drivers across Canada

Floods are the most frequently occurring natural hazard in Canada. An in-depth understanding of flood seasonality and its drivers at a national scale is essential. Here, a circular, statistics-based approach is implemented to understand the seasonality of annual-maximum floods (streamflow) and to identify their responsible drivers across Canada. Nearly 80% and 70% of flood events were found to occur during spring and summer in eastern and western watersheds across Canada, respectively. Flooding in the eastern and western watersheds was primarily driven by snowmelt and extreme precipitation, respectively. This observation suggests that increases in temperature have led to early spring snowmelt-induced floods throughout eastern Canada. Our results indicate that precipitation (snowmelt) variability can exert large controls on the magnitude of flood peaks in western (eastern) watersheds in Canada. Further, the nonstationarity of flood peaks is modelled to account for impact of the dynamic behaviour of the identified flood drivers on extreme-flood magnitude by using a cluster of 74 generalized additive models for location scale and shape models, which can capture both the linear and nonlinear characteristics of flood-peak changes and can model its dependence on external covariates. Using nonstationary frequency analysis, we find that increasing precipitation and snowmelt magnitudes directly resulted in a significant increase in 50-year streamflow. Our results highlight an east–west asymmetry in flood seasonality, indicating the existence of a climate signal in flood observations. The understating of flood seasonality and flood responses under the dynamic characteristics of precipitation and snowmelt extremes may facilitate the predictability of such events, which can aid in predicting and managing their impacts.