A Comparative Study of the Atmospheric Layers below First Lifting Condensation Level for Instantaneous Pre-Monsoon Thunderstorm Ocurence at Agartala(23°30′N,91°15′E) and Ranchi(23°14′N,85°14′E) of India

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On the heat budget of the Arabian Sea

Summary The rate of oceanic heat storage of the upper 200m of the Arabian Sea is explained in terms of net air-sea heat flux (Q _F), heat change due to horizontal divergence and vertical motion (Q _V) and heat change due to lateral advection (Q _A). The analysis revealed that the heat storage of the Arabian Sea is mainly controlled byQ _V while the effect ofQ _A is much larger than expected. Parameterisation of summer cooling revealed that the depletion of energy from the mixed layer is mainly due to upwelling and horizontal advection though large amount of heat is accumulated due to net air-sea heat flux. The annual heat balance of the upper 200m of the Arabian Sea suggested large heat gain by air-sea exchange processes. About two third of this heat gain is compensated by horizontal advection and one third by vertical advection.With 4 Figures     

Multiple episodes of tectonothermal processes in the Eastern Ghats granulite belt

A suite of rocks from Borra Carbonate Granulite Complex (BCGC) in the Eastern Ghats granulite belt displays superposed structures and overprinted mineral assemblages that reveal multiple episodes of tectonothermal reworking of the complex under granulite facies condition. Five distinct episodes of deformation (D₁, D₂, D₃, D₄ and D₅) and four phases of metamorphism (M₁, M₂, M₃ and M₄) are recorded. The signature of the earliest tectonothermal event, D₁ is a gneissic foliation (S₁) denned by segregation of peak granulite facies mineral assemblages corresponding to prograde M₁ metamorphism. M₂ metamorphic overprint represents an episode of near-isobaric cooling of the complex under a static condition. D₂ represents an episode of ductile deformation manifested by isoclinal folding (F₂) and associated extensional structures, within a broad framework of coaxial bulk deformation. The present study reveals that D₂ took place subsequent to M₂ - Subsequent deformation, D₃, produced F₃ folds and also deformations of boudins formed during D₂. M₃, which is synchronous with F₃, represents a near isothermal decompression of the BCGC. This was followed by a weak structural readjustment (D₄), producing E-W cross folds. The latter was not, however, associated with any recognizable petrological reworking. In the terminal events, deformation (D₅) and mineral reactions (M₄) were localized along narrow intersecting shear zones. The latter acted as channelways for carbonic and still later hydrous fluid infiltration. The available thermobarometric data from BCGC and other areas of the Eastern Ghats belt reveal that reworking during M₂ and M₃ ensued in a thermally perturbed regime. The high thermal regime might also have persisted during carbonic fluid infiltration related to terminal reworking (M₄).     

Synthetic Seismograms for a Layered Earth Geological Model Using the Absorption and Dispersion Phenomena

—An algorithm has been developed to compute the dispersive and dissipative seismic response using FUTTERMAN’S (1962) third attenuation-dispersion relationship. In the computation, frequency-dependent velocity and quality factor Q have been used but in the case of the nondispersive synthetic seismogram, frequency-independent velocity has been used. The model’s parameters are density, phase velocity, quality factors and thicknesses of the layers. Dispersive and nondispersive synthetic seismograms have been computed with and without absorption for a layered earth geological model. Fast Fourier transform (FFT) technique has been adopted for converting the frequency domain response into the time domain. The frequency spacing, Δf = 0.976?Hz, has been considered to avoid the aliasing effect. The results have revealed changes in the reflected waveforms in the frequency domain as well as in the time domain for absorption and dispersion cases. It is also concluded that dispersion reduces the arrival time and this effect is increasing with the travel time. The effect of constant Q on the seismic response has also been studied.     

Electron cyclotron waves in the presence of parallel electric fields in the Earth’s auroral plasma

The electron cyclotron waves that originate at low altitudes (<0.5 R_E) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions.     

Characteristics of VHF radiowave scintillations over a solar cycle (1983–1993) at a low-latitude station: Waltair (17.7°N, 83.3°E)

The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.     

Land cover dynamics in Garhwal Himalayas — a case study of balkhila sub-watershed

The present paper focuses on land cover dynamics pattern in Balkhila sub-watershed situated in Garhwal Himalayas. This study contributes example from human shaped ecosystem in mountainous regions where fragmentation of natural resources is active. The remote sensing and GIS has been used to understand the land cover dynamics along the topography. The results report that the land cover dynamics is dependent on the aspect due to sun illumination. The altitude and slope are no more a barrier for resource extraction and the human activity zone is shifting towards higher altitudes and slopes. The changes are also defined along the road and settlements.     

Seismic horizontal pullout capacity of shallow vertical anchors in sand

The concept of the equivalent free surface has been extended to determine the seismic horizontal pullout capacity of shallow vertical strip plate anchors buried in sand. The analysis has been done rigorously by using the method of stress characteristics. The results have been expressed in the form of non-dimensional charts. The pullout resistance has been found to reduce quite extensively with increase in the magnitude of horizontal earthquake acceleration. The results were compared with the previously published data, and it was seen that the computed pullout resistance with the proposed method was found to be lowest. This revised version was published online in July 2006 with corrections to the Cover Date.     

Classification and interpretation of piezometer well hydrographs in parts of southeastern peninsular India

Well hydrographs from 275 piezometers between 1998 and 2001 in the southeastern parts of peninsular India were used in this study. The area has a monsoon-type climate. Hard rocks cover 85% of the area. The form (shape) of the hydrograph depends upon (1) climatic and hydrogeologic parameters and (2) the scale of the graph. Therefore, hydrographs are drawn to a defined and standardised scale, which allows comparison of hydrographs and helps in bringing out reasons for different forms of the hydrographs. Hydrographs can be divided into seasonal segments and the slope of each segment then used as the basic element of a classification scheme. Slopes are classed as flat (inclination <20°), obtuse (between 20 and 45°), acute (45 and 80°), right angled (80 and 90°) and homoclinal (segments of hydrographs are either rising or falling during one complete water year). Hydrographs are assigned names that are a combination of these classes and begin with the rising segment, such as acute-obtuse. Seventy-six percent of segments were homoclinal-falling in 1999, which had a poor monsoon. Flat segments constitute 27% of all segments in confined Mesozoic aquifer systems. Water table fluctuations suggest an approximate recharge of 120 to 180 mm per annum constituting 18% of the annual precipitation. Cumulative rainfall required to affect a rise in water table is between 45 to 200 mm and lag time varies from 30 minutes to 200 rainy days, which suggests that moisture in the vadose zone holds a part of the annual replenishment for these aquifers.