H α Observations of 8 June, 2004 Venus Transit     

Ashok Ambastha  B. Ravindra  Sanjay Gosain 《Solar physics》2006,233(1):171-184

The cosmic event of Venus transit across the solar disk occurred on 8 June, 2004. The previous such event was witnessed about 122 years ago on 6 December, 1882. We observed this rare transit in H _α 6563 Å line-center from Udaipur Solar Observatory (USO) using both the full-disk and small field-of-view solar telescopes. In the earlier historical transits, a “black-drop” effect was observed in white light images, during the contact phases. The transit of 8 June, 2004 provided a unique opportunity to observe this effect, for the first time, in H _α. We report that the “black-drop” effect is present in H _α also, as in the white light observations made by the ground-based Global Oscillation Network Group (GONG) instrument and the space-borne Transition Region and Coronal Explorer (TRACE) satellite. We did not observe any noticeable “aureole” (atmospheric glow) around Venus during the ingress or egress phases. We have compared the H _α images with the multi-wavelength data obtained from the TRACE satellite.  相似文献   

Water Balance Study for a Basin Integrating Remote Sensing Data and GIS     

Sanjay Kumar Jain  Sharad K. Jain  V. Hariprasad  Anju Choudhry 《Journal of the Indian Society of Remote Sensing》2011,39(2):259-270

Water balance of a basin involves estimation of input precipitation, runoff, infiltration and evapotranspiration (ET). Although ET may have large variations over a big basin, it is commonly estimated using a few point measurements and this makes the estimation error prone. Satellite based remote sensing data provides few parameters for estimation of energy fluxes, at the land surface and atmosphere interaction in a distributed manner using the meteorological parameters. These parameters through surface energy balance equation have been used for the estimation of ET in this study. Various spatially distributed variables required for ET estimation; viz. NDVI, surface albedo, surface temperature etc. have been derived using remote sensing and ancillary data for Tapi basin located in western India. Beside this field data such as rainfall, air temperature, relative humidity, sunshine hours etc. have been used. For computation of runoff, Soil Conservation Services (SCS) approach has been considered. Tapi basin up to Ukai dam has been selected as the study area. Satellite data from National Oceanic and Atmospheric Administration (NOAA), Polar Orbiting Environmental Satellite, which carries the Advanced Very High Resolution Radiometer (AVHRR), have been used for preparation of various maps required for runoff and ET analysis. The results of runoff and ET have been compared with observed data for 2 years, 2002–2003 and the results have been found in good agreement with observed data.  相似文献   

Performance Enhancement of Solar Latent Heat Thermal Storage System with Particle Dispersion — an Exergy Approach     

Selvaraj Jegadheeswaran  Sanjay D. Pohekar  Tarik Kousksou 《洁净——土壤、空气、水》2011,39(10):964-971

Phase change material (PCM) employed latent heat thermal storage (LHTS) system has been showing good potential over the years for energy management, particularly in solar energy systems. However, enhancement in thermal conductivity of PCMs is emphasized as PCMs are known for their poor thermal conductivity. In this work, the thermal performance of a shell and tube LHTS module containing PCM‐metal particles composite is investigated while charging and is compared with that of pure PCM system. The effect of particle dispersion on latent heat capacity of pure PCM is also analyzed. Enthalpy based governing equations are solved numerically adopting FLUENT code. Exergy based performance evaluation is taken as a main aspect. The numerical results are presented for various operating conditions of heat transfer fluid (HTF) and indicate considerable performance improvement of the system when particles are dispersed.  相似文献   

Trace elements geochemistry and petrogenesis of basalt from the southern part of the East Pacific Rise     

Sanjay Kumar Pandey  Sucharita Pal  J. P. Shrivastava  G. S. Roonwal 《Journal of the Geological Society of India》2013,81(1):91-100

Trace element geochemistry of basalt samples collected from 6°S-24°S of the southern EPR, representing a super-fast spreading axis is discussed. Trace element data classify these basalts into Normal and Transitional types of MORB, however, LREE enrichment is also observed in few of them. Chondrite normalized REE data plots show highly fractionated nature of these lavas, suggesting their derivation from the primitive mantle source. Petrogenetic modeling of the data suggests variation in the solidus pressure (14–20 kb.) and temperature (1316–1425°C), where 15 to 20% partial melting of the mantle is accountable for the generation of the melt. The pressure and temperature conditions at the beginning of the mantle melting were high along higher latitudes (24°S of EPR), but it gradually lowered down in the lower latitudinal areas (6°S of EPR), supporting for the presence of passively rising upper mantle beneath the Southern EPR.  相似文献   

Physically-based distributed soil erosion and sediment yield model (DREAM) for simulating individual storm events     

RAAJ Ramsankaran  Umesh Chandra Kothyari  Sanjay Kumar Ghosh  Andreas Malcherek  Krishnan Murugesan 《水文科学杂志》2013,58(4):872-891

Abstract

A relatively simple process-oriented, physically-based distributed (PBD) hydrological model, the distributed runoff and erosion assessment model (DREAM), is described, and a validation study conducted in the semi-forested watershed of Pathri Rao, in the Garhwal Himalayas, India, is reported. DREAM takes account of watershed heterogeneity as reflected by land use, soil type, topography and rainfall, measured in the field or estimated through remote sensing, and generates estimates of runoff and sediment yield in spatial and temporal domains. The model is based on simultaneous solution of flow dynamics, based on kinematic wave theory, followed by solution of soil erosion dynamics. As the storm rainfall proceeds, the process of overland flow generation is dependent on the interception storage and infiltration rates. The components of the soil erosion model have been modified to provide better prediction of sediment flow rates and sediment yields. The validation study conducted to test the performance of the model in simulating soil erosion and sediment yield during different storm events monitored in the study watershed showed that the model outputs are satisfactory. Details of a sensitivity analysis, model calibration and the statistical evaluation of the results obtained are also presented and discussed. It is noteworthy that the distributed nature of the model combined with the use of geographical information system (GIS) techniques permits the computation and representation of the spatial distribution of sediment yield for simulated storm events, and a map of the spatial distribution of sediment yield for a simulated storm event is presented to highlight this capability.

Citation Ramsankaran, R., Kothyari, U.C., Ghosh, S.K., Malcherek, A., and Murugesan, K., 2013. Physically-based distributed soil erosion and sediment yield model (DREAM) for simulating individual storm events. Hydrological Sciences Journal, 58 (4), 872–891.  相似文献   

EnVision: taking the pulse of our twin planet     

Richard C. Ghail  Colin Wilson  Marina Galand  David Hall  Chris Cochrane  Philippa Mason  Joern Helbert  Franck MontMessin  Sanjay Limaye  Manish Patel  Neil Bowles  Daphne Stam  Jan-Erik Wahlund  Fabio Rocca  David Waltham  Tamsin A. Mather  Juliet Biggs  Matthew Genge  Philippe Paillou  Karl Mitchell  Lionel Wilson  Upendra N. Singh 《Experimental Astronomy》2012,33(2-3):337-363

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Semitransparent cirrus clouds in the tropical tropopause layer during two contrasting seasons     

S.V. Sunilkumar  K. Parameswaran  K. Rajeev  B.V. Krishna Murthy  S. Meenu  Sanjay K. Mehta  Asha Babu 《Journal of Atmospheric and Solar》2010,72(9-10):745-762

Association between semitransparent cirrus (STC) and tropospheric dynamics during the two contrasting seasons (Summer-monsoon and Winter) is studied using lidar and MST radar observations at Gadanki (13.5°N, 79.2°E) along with data from Geo-stationary satellite (KALPANA-1). The tropical tropopause layer (TTL) is found to be very conducive for the formation of STC. For those thicker STCs forming within TTL, the cloud top remains mostly steady with the top of the TTL, while the cloud base varies significantly in accordance with the altitude extent of tropospheric convective outflow. Based on depolarization characteristics of STCs (from lidar) along with regional distribution of tropospheric clouds derived from satellite data, altitude profile of horizontal wind, wind field at 150 hPa and air mass back trajectories, it can be reasonably inferred that, while the multi-layered and highly structured STCs during the monsoon period originate mostly from the deep convections, the sub-visual/ultra thin STCs during winter could mostly be of in situ origin.  相似文献   

Study of effects of focal depth on the characteristics of Rayleigh waves using finite difference method     

Jay P. Narayan  Sanjay Kumar 《Acta Geophysica》2010,58(4):624-644

This paper presents a relationship between the focal depth in terms of Rayleigh-wave wavelength and the dominant frequency of Rayleigh waves generated in a homogeneous half-space. Rayleigh waves were simulated using a (2, 4) staggered grid P-SV wave finite difference algorithm with VGR-stress imaging technique as a free surface boundary condition. VGR is an acronym for vertical grid-size reduction. The simulated seismic responses using P-wave and SV-wave sources at different focal depths revealed Rayleigh-wave generation up to certain focal depth only for the considered frequency bandwidth. A shift of normalized spectral shape of Rayleigh wave towards lower frequency with increasing focal depth was inferred. Largest spectral amplitude was obtained in the wavelength for which the ratio of focal depth to the wavelength of Rayleigh wave was around 0.17 in the case of P-wave source and 0.9 in the case of SV-wave source. An exponential decrease of spectral amplitude of Rayleigh wave with the departure of the ratio of focal depth to Rayleigh wave wavelength from the above mentioned values was obtained.  相似文献   

On northward movement of convergence zones along west coast of India in a real-time forecast     

S. Taraphdar  J. Sanjay  P. Mukhopadhyay 《Meteorology and Atmospheric Physics》2009,104(3-4):177-189

The present study addresses the depiction of regional features in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) real-time products associated with the onset of Indian summer monsoon 2006 along the west coast of India. This study attempts to understand some atmospheric dynamical processes that give rise to the northward shifting of the convergence zones in the sub-daily scale leading to the onset over Mumbai. The comparison of analysis and forecast shows that NCEP GFS appears to follow the analysis till 24 h, but deviates thereafter. The most notable feature in analyses is the distinct meridional asymmetries in the vorticity field with respect to the convection center. It is identified that the equivalent barotropic structure of vorticity north of the convection center is the main forcing for the northward movement of convergence zones. The composite meridional–vertical structure of each term in the vorticity budget reveals the importance of convective term in the upper atmosphere (700–200 hPa) and the stretching term in the lower atmosphere (1,000–700 hPa) with a lesser contribution of the tilting term. From an analysis of a simplified vorticity equation by retaining these dominant terms and by comparing the evolution of the diabatic heating, it is concluded that the inaccuracies in the model’s representation of convection led to the weakening of barotropic westerlies in the forecast.  相似文献   

A new mixing technique for solidifier and dredged fill in coastal area     

Wenhui Shi  Sanjay Nimbalkar  Wenbai Liu 《Marine Georesources & Geotechnology》2017,35(1):52-61

One of the major drawbacks of the conventional method of land reclamation, which involves mixing cement with the dredged soils at the disposal site, is the high cost associated with its manufacturing and transportation. In this study, a new solidified dredged fill (SDF) technique and a new additive are proposed and their practical applications are discussed. Unlike the conventional approach, the dredged marine soils were mixed with the solidifiers using a newly designed mixing technique prior to its transport to site, which would significantly reduce the cost of site machinery and effectively reclaim land with adequate engineering properties necessary for the construction of infrastructure. To evaluate the performance of the reclaimed land using the proposed technique, a series of laboratory and field tests (namely, static and dynamic cone penetration tests, and plate load tests) were conducted on grounds filled with and without solidified dredged marine soils, respectively. The results showed that the engineering behavior of the reclaimed land with dredged marine soils using SDF technique had significantly improved. The SDF technique combined with the newly designed mixing system improved the performance of ground and has thus proved to be both cost-effective and safe.  相似文献