Cloud — Aerosol interaction during lightning activity over land and ocean: Precipitation pattern assessment

The present study attempts to identify the land - ocean contrast in cloud - aerosol relation during lightning and non-lightning days and its effect on subsequent precipitation pattern. The thermal hypothesis in view of Convective Available Potential Energy (CAPE) behind the land - ocean contrast is observed to be insignificant in the present study region. The result shows that the lightning activities are significantly and positively correlated with aerosols over both land and ocean in case of low aerosol loading whereas for high aerosol loading the correlation is significant but, only over land. The study attempts to comprehend the mechanism through which the aerosol and lightning interact using the concept of aerosol indirect effect that includes the study of cloud effective radius, cloud fraction and precipitation rate. The result shows that the increase in lightning activity over ocean might have been caused due to the first aerosol indirect effect, while over land the aerosol indirect effect might have been suppressed due to lightning. Thus, depending on the region and relation between cloud parameters it is observed that the precipitation rate decreases (increases) over ocean during lightning (non-lightning) days. On the other hand during non-lightning days, the precipitation rate decreases over land.     

The evolution of the Palim granite in the Bastar tin province, Central India

Summary The Palim granite, hosted by the metasedimentary country rocks in the Bastar tin province, is a heterogeneous pluton that comprises hornblende granite, biotite granite and two-mica granite. Spherical inhomogeneous surmicaceous enclaves occur within the granites with coarse grained cores of muscovite mantled by finer muscovite-quartz-biotite (± sillimanite) rims. Geochemical features imply that the granites are highly evolved and geochemically distinct. Petrographic and geochemical considerations point towards a transition from metaluminous I-type hornblende-bearing granite in the south to peraluminous volatile-enriched S-type like lithologies (biotite and two-mica granites) towards north. Modeling of highly incompatible elements such as Nb and Cs, implies 31 to 33% assimilated fractional crystallization of a melt with an initial composition close to that of the hornblende granite to form the two-mica granite. Hornblende geobarometry, plagioclase-hornblende thermometry (in hornblende granite) and phengite barometry (in two-mica granite), yield P-T estimates of 5–7 kb/725°–760 °C, and 6 kb/700 °C, respectively. The study further implies that a genetic link exists between granite magmatism and the formation of tin pegmatites in the region. The preponderance of peripheral pegmatites to the north-east of the Palim granite is regarded a result of outward crystal-melt fractionation and tectonic tilting of the pluton. Received October 21, 1999; revised version accepted December 12, 2000     

First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS)

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of M_w 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.     

Cyclone track prediction using INSAT data

INSAT visible and infrared imageries of three cyclones in the Bay of Bengal during the period 1984–1987 were analysed with a view to improve the cyclone track prediction in this region. It was observed that the rotation in the major structural cloud features (as seen from the cloud-top temperature maps) associated with these cyclones in the Bay of Bengal is followed with a change in direction of their movement. This method is seen to be particularly effective when the cyclone is severe and when the major cloud features persist for a reasonably longer time. In the present study, only the direction of movement is forecast assuming a uniform speed of the cyclone.     

Hydrophysical aspects of oxygen regime formation in a shallow ice-covered lake

Long-term observational data on a small, shallow Lake Vendyurskoe (Karelia) were used to analyze the space and time dissolved-oxygen dynamics in winter. Biochemical consumption was found to play a leading role in the reduction of dissolved-oxygen concentration in lake water in winter. The total decrease in the amount of dissolved oxygen since the beginning of under-ice period until mid-April was shown to amount to one third of the initial value. The year-to-year variations in winter oxygen consumption are ~10%, suggesting the process to be stable in the years of observations. The rate of oxygen consumption and variations in dissolved oxygen content of lake water in winter were evaluated. The analysis and literary data allow us to conclude that the hydrophysical processes taking place in shallow lakes in winter have a considerable effect on their oxygen regime.     

Seismic site characterization and site response study of Nirsa (India)

Natural Hazards - The Nirsa block, a coal mining area, and an industrial town lies in the southern part of Dhanbad district, at the border between the Indian states of Jharkhand and West Bengal....     

Land use alterations and its possible impact on premonsoon climatic variables

Changes in land surface characteristics have become a matter of great concern in the recent years. It is particularly important when the mesoscale phenomena control the climatic variables of a region. Gangetic West Bengal with its neighbourhood is such a region where during premonsoon season, mesoscale phenomena, i.e., sea breeze circulation and severe convective development, control the local climate of the season. It is also reported that a drastic changes in land use pattern has taken place in recent period over the region, which might affect the local climate, resulting in severe water crisis over the semi-arid part of the region. A detailed study has been undertaken to investigate the changes in land use pattern through satellite data over the area and its possible impact on the local climate through numerical modeling. Satellite (IRS-IC and Landsat 4 and 5) data shows a sharp change in dynamic vegetation during this period, which is due to, increased agricultural practices in the recent years. Mesoscale model indicates that agricultural practices hinder the development of sea breezes over the coastal and inland places, causing less incursion of moisture towards inland. This may be associated with less number of convective developments over the coastal and neighbouring places.     

Linear homotopy solution of nonlinear systems of equations in geodesy

A fundamental task in geodesy is solving systems of equations. Many geodetic problems are represented as systems of multivariate polynomials. A common problem in solving such systems is improper initial starting values for iterative methods, leading to convergence to solutions with no physical meaning, or to convergence that requires global methods. Though symbolic methods such as Groebner bases or resultants have been shown to be very efficient, i.e., providing solutions for determined systems such as 3-point problem of 3D affine transformation, the symbolic algebra can be very time consuming, even with special Computer Algebra Systems (CAS). This study proposes the Linear Homotopy method that can be implemented easily in high-level computer languages like C++ and Fortran that are faster than CAS by at least two orders of magnitude. Using Mathematica, the power of Homotopy is demonstrated in solving three nonlinear geodetic problems: resection, GPS positioning, and affine transformation. The method enlarging the domain of convergence is found to be efficient, less sensitive to rounding of numbers, and has lower complexity compared to other local methods like Newton–Raphson.