Diffraction of SH-Waves in a Spherically Isotropic Medium by a Rigid or Fluid Spherical Core     

Subhendu K. Datta  Arvind H. Shah 《Geophysical Journal International》1970,21(1):33-46

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A new semiconductor thermometer for geothermal measurements     

Satyabrata Datta 《Pure and Applied Geophysics》1965,61(1):123-126

Summary A portable solid state device designed and constructed for the measurement of temperature variation with depth inside a borehole is described. Saturation current (which is highly dependent on ambient temperature) in a reverse biased PN junction has been utilised for the purpose of measurement. The equipment is inexpensive and possesses several advantages over other types of instruments for geothermal measurement regarding simplicity in construction and operation.The paper is published by the kind permission of the Director General, Geological Survey of India.  相似文献   

South Equatorial Current (SEC) driven changes at DSDP Site 237, Central Indian Ocean, during the Plio-Pleistocene: Evidence from Benthic Foraminifera and Stable Isotopes   总被引：1，自引：0，他引：1  

Anil K. Gupta  Moumita Das  K. Bhaskar 《Journal of Asian Earth Sciences》2006,28(4-6):276-290

This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum–Uvigerina proboscidea (Au–Up), Pullenia bulloides–Bulimina striata (Pb–Bs), Globocassidulina tumida–Nuttallides umbonifera (Gt–Nu), Gyroidinoides nitidula–Cibicides wuellerstorfi (Gn–Cw) and Cassidulina carinata–Cassidulina laevigata (Cc–Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au–Up and Pb–Bs biofacies), dominate the early Pliocene interval (5.6–4.5 Ma) of global warmth. An intense Indo-Pacific ‘biogenic bloom’ and strong Oxygen Minimum Zone extended to intermediate depths (1000–2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt–Nu, Gn–Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc–Cl biofacies).  相似文献   

Variation of ambient SO2 over Delhi     

A. Datta  T. Saud  A. Goel  S. Tiwari  S. K. Sharma  M. Saxena  T. K. Mandal 《Journal of Atmospheric Chemistry》2010,65(2-3):127-143

The temporal variation of ambient SO₂ and the chemical composition of particulate matters (PM_2.5 and PM₁₀) were studied at National Physical Laboratory (NPL), New Delhi (28°38′N, 77°10′E). Spatial variation of SO₂ at seven air quality monitoring stations over Delhi was also studied simultaneously. Wide range of ambient SO₂ was recorded during winter (2.55 to 17.43 ppb) compare to other seasons. SO₂ mixing ratio was recorded significantly high at industrial sites during winter and summer; however, no significant spatial difference in SO₂ mixing ratio was recorded during monsoon. SO ₄ ^2? /(SO₂+SO ₄ ^2? ) ratio was recorded high (0.74) during winter and low (0.69) during summer. Monthly variation of PSCF was analyzed using HYSPLIT seven days backward trajectories and daily average SO₂ data. PSCF analysis suggests that, during winter (December, January, February) ambient SO₂ at the study site might have contributed from long distance sources, located towards west and southwest directions; during monsoon (July, August, September) marine contribution was noticed; whereas, during summer (April, May and June) it was from regional sources (located within few 100 km of study site). During winter there was significant contribution from the long distance sources located in western Asia, northwestern Pakistan, Rajasthan and Punjab provinces of India. Coal used in thermal power plants at Panipat (in the northwestern side) and Faridabad (in the southeastern side), local industries, soil erosion and biomass burning may be major contributing factors for SO₂ during summer. The study establishes that the transport sector may not be the major source of ambient SO₂ in Delhi.  相似文献   

Stormwater control impacts on runoff volume and peak flow: A meta-analysis of watershed modelling studies     

Colin D. Bell  Jordyn M. Wolfand  Chelsea L. Panos  Aditi S. Bhaskar  Ryan L. Gilliom  Terri S. Hogue  Kristina G. Hopkins  Anne J. Jefferson 《水文研究》2020,34(14):3134-3152

Decades of research has concluded that the percent of impervious surface cover in a watershed is strongly linked to negative impacts on urban stream health. Recently, there has been a push by municipalities to offset these effects by installing structural stormwater control measures (SCMs), which are landscape features designed to retain and reduce runoff to mitigate the effects of urbanisation on event hydrology. The goal of this study is to build generalisable relationships between the level of SCM implementation in urban watersheds and resulting changes to hydrology. A literature review of 185 peer-reviewed studies of watershed-scale SCM implementation across the globe was used to identify 52 modelling studies suitable for a meta-analysis to build statistical relationships between SCM implementation and hydrologic change. Hydrologic change is quantified as the percent reduction in storm event runoff volume and peak flow between a watershed with SCMs relative to a (near) identical control watershed without SCMs. Results show that for each additional 1% of SCM-mitigated impervious area in a watershed, there is an additional 0.43% reduction in runoff and a 0.60% reduction in peak flow. Values of SCM implementation required to produce a change in water quantity metrics were identified at varying levels of probability. For example, there is a 90% probability (high confidence) of at least a 1% reduction in peak flow with mitigation of 33% of impervious surfaces. However, as the reduction target increases or mitigated impervious surface decreases, the probability of reaching the reduction target also decreases. These relationships can be used by managers to plan SCM implementation at the watershed scale.  相似文献   

Variability and teleconnections of South and East Asian summer monsoons in present and future projections of CMIP5 climate models     

Bhaskar Preethi  Milind Mujumdar  Amita Prabhu  Ramesh Kripalani 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(2):305-325

Coupled Model Inter-comparison Project Phase 5 (CMIP5) model outputs of the South and East Asian summer monsoon variability and their tele-connections are investigated using historical simulations (1861-2005) and future projections under the RCP4.5 scenario (2006-2100). Detailed analyses are performed using nine models having better representation of the recent monsoon teleconnections for the interactive Asian monsoon sub-systems. However, these models underestimate rainfall mainly over South Asia and Korea-Japan sector, the regions of heavy rainfall, along with a bias in location of rainfall maxima. Indeed, the simulation biases, underestimations of monsoon variability and teleconnections suggest further improvements for better representation of Asian monsoon in the climate models. Interestingly, the performance of Australian Community Climate and Earth System Simulator version 1.0 (ACCESS1.0) in simulating the annual cycle, spatial pattern of rainfall and multi-decadal variations of summer monsoon rainfall over South and East Asia appears to more realistic. In spite of large spread among the CMIP5 models, historical simulations as well as future projections of summer monsoon rainfall indicate multi-decadal variability. These rainfall variations, displaying certain epochs of more rainfall over South Asia than over East Asia and vice versa, suggest an oscillatory behaviour. Teleconnections between South and East Asian monsoon rainfall also exhibit a multi-decadal variation with alternate epochs of strengthening and weakening relationship. Furthermore, large-scale circulation features such as South Asian monsoon trough and north Pacific subtropical high depict zonal oscillatory behaviour with east-west-east shifts. Periods with eastward or westward extension of the Mascarene High, intensification and expansion of the upper tropospheric South Asian High are also projected by the CMIP5 models.  相似文献   

Simulation of Tropical Cyclone Circulation over Bay of Bengal Using the Arakawa-Schubert Cumulus Parametrization. Part I — Description of the Model, Initial Data and Results of the Control Experiment     

D. V. Bhaskar Rao  K. Ashok 《Pure and Applied Geophysics》1999,156(3):525-542

—A ten-level axi-symmetric primitive equation model with cylindrical coordinates is used to simulate the tropical cyclone evolution from a weak vortex for the Bay of Bengal region. The physics of the model comprises the parameterization schemes of Arakawa-Schubert cumulus convection (Lord et al., 1982) and Deardorff’s (1972) planetary boundary layer. The initial conditions have been taken from the climate mean data for November of Port Blair (92.4 E, 11.4 N) in the Bay of Bengal, published by the India Meteorological Department. An initial vortex has been designed to have tangential wind maximum of 10 m/s at 120-km radius with a central surface pressure of 1008 hPa. As a control experiment, referred to as ASBB1, the model is integrated for 240 h maintaining the sea-surface temperature (SST) constant at 301 K. The results of the control experiment reveal a slow decrease of the Central Surface Pressure (CSP) from the initial value of 1008 hPa to 970 hPa at 156 h. After 156 h the CSP decreased sharply until 186 h, attaining 890 hPa. The tangential wind at 1 km level attained the Cyclone Threshold Intensity (CTI) of 17 m/s around 78 h and a maximum of 87 m/s was found at 210 h. These features indicate a predeveloping stage up to 156 h, a deepening stage of 30 h from 156–186 h followed by the mature stage. The mature stage is characterized by the simulation of the central eye region, warm core, strong cyclonic circulation in the central 300 km with low-level inflow; strong vertical motion at the eye wall and outflow aloft. The convection features of the different cloud types conform with the circulation features. The control experiment clearly indicates the evolution of a cyclone with hurricane intensity from a weak vortex. In part two of the paper, results from sensitivity experiments with respect to variations in latitude, SST and initial thermodynamic state have been presented.  相似文献   

Assessment of land use land cover change impact on hydrological regime of a basin     

Vaibhav Garg  S. P. Aggarwal  Prasun K. Gupta  Bhaskar R. Nikam  Praveen K. Thakur  S. K. Srivastav  A. Senthil Kumar 《Environmental Earth Sciences》2017,76(18):635

The sustainability of water resources mainly depends on planning and management of land use; a small change in it may affect water yield largely, as both are linked through relevant hydrological processes, explicitly. However, human activities, especially a significant increase in population, in-migration and accelerated socio-economic activities, are constantly modifying the land use and land cover (LULC) pattern. The impact of such changes in LULC on the hydrological regime of a basin is of widespread concern and a great challenge to the water resource engineers. While studying these impacts, the issue that prevails is the selection of a hydrological model that may be able to accommodate spatial and temporal dynamics of the basin with higher accuracy. Therefore, in the present study, the capabilities of variable infiltration capacity hydrological model to hydrologically simulate the basin under varying LULC scenarios have been investigated. For the present analysis, the Pennar River Basin, Andhra Pradesh, which falls under a water scarce region in India, has been chosen. The water balance components such as runoff potential, evapotranspiration (ET) and baseflow of Pennar Basin have been simulated under different LULC scenarios to study the impact of change on hydrological regime of a basin. Majorly, increase in built-up (13.94% approx.) and decrease in deciduous forest cover (2.44%) are the significant changes observed in the basin during the last three decades. It was found that the impact of LULC change on hydrology is balancing out at basin scale (considering the entire basin, while routing the runoff at the basin outlet). Therefore, an analysis on spatial variation in each of the water balance components considered in the study was done at grid scale. It was observed that the impact of LULC is considerable spatially at grid level, and the maximum increase of 265 mm (1985–2005) and the decrease of 48 mm (1985–1995) in runoff generation at grid were estimated. On the contrary, ET component showed the maximum increase of 400 and decrease of 570 mm under different LULC change scenario. Similarly, in the base flow parameter, an increase of 70 mm and the decrease of 100 mm were observed. It was noticed that the upper basin is showing an increasing trend in almost all hydrological components as compared to the lower basin. Based on this basin scale study, it was concluded that change in the land cover alters the hydrology; however, it needs to be studied at finer spatial scale rather than the entire basin as a whole. The information like the spatial variation in hydrological components may be very useful for local authority and decision-makers to plan mitigation strategies accordingly.  相似文献   

Observed oceanic response to tropical cyclone Jal from a moored buoy in the south-western Bay of Bengal   总被引：1，自引：1，他引：0  

M. S. Girishkumar  K. Suprit  Jayaram Chiranjivi  T. V. S. Udaya Bhaskar  M. Ravichandran  R. Venkat Shesu  E. Pattabhi Rama Rao 《Ocean Dynamics》2014,64(3):325-335

Upper oceanographic and surface meteorological time-series observations from a moored buoy located at 9.98°N, 88°E in the south-western Bay of Bengal (BoB) were used to quantify variability in upper ocean, forced by a tropical cyclone (TC) Jal during November 2010. Before the passage of TC Jal, salinity and temperature profiles showed a typical BoB post-monsoon structure with relatively warm (30 °C) and low-saline (32.8 psu) waters in the upper 30- to 40-m layer, and relatively cooler and higher salinity (35 psu) waters below. After the passage of cyclone, an abrupt increase of 1 psu (decrease of 1 °C) in salinity (temperature) in the near-surface layers (up to 40-m depth) was observed from buoy measurements, which persisted up to 10–12 days during the relaxation stage of cyclone. Mixed layer heat budget analysis showed that vertical processes are the dominant contributors towards the observed cooling. The net surface heat flux and horizontal advection together contributed approximately 33 % of observed cooling, during TC Jal forced stage. Analysis showed the existence of strong inertial oscillation in the thermocline region and currents with periodicity of ～2.8 days. During the relaxation stage of the cyclone, upward movement of thermocline in near-inertial frequencies played significant role in mixed layer temperature and salinity variability, by much freer turbulent exchange between the mixed layer and thermocline.  相似文献   

Role of Vertical Resolution in Numerical Models Towards the Intensification,Structure and Track of Tropical Cyclones     

D. V. Bhaskar Rao  D. Hari Prasad  D. Srinivas  Y. Anjaneyulu 《Marine Geodesy》2013,36(4):338-355

The impact of vertical resolution on the evolution and movement of tropical cyclones was studied using NCAR MM5 model with a horizontal resolution of 9 km. Four numerical experiments were performed with different vertical resolutions, that is, with 23 vertical levels as control experiment, and 36 vertical levels with high resolution in the lower troposphere, 33 vertical levels with high resolution in the upper troposphere and 46 vertical levels with increased vertical resolution throughout the troposphere as relative to base experiment. The results indicate that increased vertical resolution in the lower troposphere produces efficient intensification and better structure in terms of eye and eyewall. Increased vertical resolution at lower levels improves the prediction of vertical shear of horizontal wind. Experiments with high resolution in the lower troposphere and high resolution throughout the troposphere simulate better track up to 72 hours.  相似文献