Diffuse solar radiation and associated meteorological parameters in India     

A. B. Bhattacharya  S. K. Kar  R. Bhattacharya 《Annales Geophysicae》1997,14(10):1051-1059

Solar diffuse radiation data including global radiation, shortwave and longwave balances, net radiation and sunshine hours have been extensively analyzed to study the variation of diffuse radiation with turbidity and cloud discharges appearing in the form of atmospherics over the tropics. Results of surface radiation measurements at Calcutta, Poona, Delhi and Madras are presented together with some meteorological parameters. The monthly values of diffuse radiation and the monthly ratios of diffuse to global solar radiation have been examined, with a special emphasis in relation to the noise level of atmospherics at Calcutta in the very low frequency band. The results exhibit some definite seasonal changes which appear to be in close agreement with one another.  相似文献   

Oxygen and hydrogen isotopic ratios in groundwaters and river waters from India     

S. K. Bhattacharya  S. K. Gupta  R. V. Krishnamurthy 《Journal of Earth System Science》1985,94(3):283-295

A comprehensive set of measurements of oxygen and hydrogen isotopic ratios in groundwaters as well as waters from rivers, lakes, hot springs etc. taken from a variety of locations in India has been carried out for the first time. Isotopically the most depleted samples occur in the high altitude precipitations in the Himalayas e.g. in the lakes of Bhutan and the source water of the Ganga. The shallow groundwater data display a continental effect where the heavy isotope content decreases with distance from the coast (about 4 to 6 per mil decrease in δ¹⁸O per 1000 km). The δ D and δ¹⁸O of these fresh waters are linearly related and an analysis of this relation vis-a-vis the meteoric water line shows the unambiguous effect of enrichment due to evaporation from soils.  相似文献   

An orthopyroxene-garnet thermometer and its application to the Madras charnockites   总被引：5，自引：0，他引：5  

S. K. Sen  A. Bhattacharya 《Contributions to Mineralogy and Petrology》1984,88(1-2):64-71

  相似文献   

Grenvillian thermal event and remnant charnockite: Isotopic evidence from the Chilka Lake granulite-migmatite suite in the Eastern Ghats belt, India   总被引：1，自引：0，他引：1  

S. Bhattacharya  M. P. Deomurari  W. Teixeira 《Journal of Earth System Science》2002,111(4):391-399

Spectacular exposures of granulite-migmatite occur in the Chilka Lake area of the Eastern Ghats belt. The garnetiferous granite gneiss of peraluminous granitic composition, often contains restitic metapelite inclusions and is demonstrably a product of biotite-dehydration melting in pelitic rocks. On the other hand, older layers and bands of charnockitic rocks frequently occur as dismembered patches within the peraluminous granite, thus imparting a measled appearance of the granite exposures. The partial melting and emplacement of the peraluminous granite represent the Grenvillian thermal event, as evidenced by Rb-Sr whole rock and Pb-Pb zircon dating. On the other hand, minor patches of charnockite represent migmatized relict, as evidenced by some older zircons, in addition to those of Grenvillian age.  相似文献   

Comparison of three remote sensing based models for the estimation of latent heat flux over India     

R. Eswar  B. K. Bhattacharya 《水文科学杂志》2017,62(16):2705-2719

The aim of this work is to compare three remote sensing based models: two contextual and one physically-based single-pixel model for the estimation of daytime integrated latent heat flux without the use of any ground measurements over Indian ecosystems. Satellite datasets from the MODIS sensors aboard the Terra and the Aqua satellites were used. The latent heat flux estimated from the remote sensing models was compared with that estimated from Bowen ratio energy balance towers at five sites in India. The root mean square error (RMSE) of the latent heat flux estimated from the contextual and the physically-based models was found to be in the order of 40 and 70 W m^?2, respectively. The relatively inferior performance of the more complex physically-based model in comparison with the contextual models was found to be largely due to inaccurate parameterizations estimated only from remote sensing datasets without any ground data.  相似文献   

亚致死剂量铜对文昌鱼和玫瑰无须的组织病理学影响     

韩莉  郭斌 《中国海洋大学学报(自然科学版)》2008,38(1):95-102

采用半静水实验法测试研究了重金属Cu2 对文昌鱼(Branchiostoma belcheri)和玫瑰无须(Puntius conchonius)的急性致死毒性和亚急性毒性.实验结果表明,Cu2 对文昌鱼和玫瑰无须 24,48,72,96 h的半致死浓度分别为0.561,0.373,0.261,0.211 mg/L及0.976,0.783,0.562,0.473 mg/L,其安全质量浓度分别为0.021和0.047 mg/L.亚急性毒性实验中,文昌鱼和玫瑰无须 分别用浓度为20%和30%的 96 h LC50的Cu2 处理.不同器官的组织病理学观察结果表明,过量Cu2 对玫瑰无须 的鳃、肝脏、肾脏等器官产生毒害,对文昌鱼鳃和肝盲囊细胞也产生了严重的毒害,表现为细胞空泡化等明显的结构破坏.实验结果显示文昌鱼的肝盲囊和脊椎动物的肝脏一样,也是受过量铜显著毒害的主要靶器官器官.因此,文昌鱼的肝盲囊至少在经受过量Cu2 毒害方面与脊椎动物肝脏具有相似性,从生理功能方面为类文昌鱼祖先的盲囊(digestive caecum)是脊椎动物肝脏的前体这一假说提供了资料.  相似文献   

A review of human and natural changes in Maya Lowland wetlands over the Holocene     

Tim Beach  Sheryl Luzzadder-Beach  Nicholas Dunning  John Jones  Jon Lohse  Tom Guderjan  Steve Bozarth  Sarah Millspaugh  Tripti Bhattacharya 《Quaternary Science Reviews》2009,28(17-18):1710-1724

In the Maya Lowlands of Mexico, Belize, and Guatemala two main types of wetlands have played important roles in human history: bajos or intermittently wet environments of the upland, interior Yucatán and perennial wetlands of the coastal plains. Many of the most important Maya sites encircle the bajos, though our growing evidence for human–wetland interactions is still sparse. The deposits of these wetlands record two main eras of slope instability and wetland aggradation: the Pleistocene–Holocene transition as rainfall increased and forests eclipsed savannas and the Maya Preclassic to Classic as deforestation, land-use intensity, and drying increased. The ancient Maya adapted with terraces around these bajo margins but retracted in the Late Preclassic in some areas. The perennial wetlands of the coastal plains have different histories, and the first conceptual model of human–wetland interaction described intensive wetland agriculture in the Preclassic through Classic based on raised fields and canals. But a second model arose that interpreted the wetland stratigraphy and canals as more indicative of natural aggradation by accelerated erosion and gypsum precipitation that buried Archaic and Preclassic fields and there was little Classic era use. We present new data on a third and fourth model in this study. The third is a hybrid of the models one and two, including the Archaic to Preclassic aggradation of the second model, and the first model's Classic period fields and canals as piecemeal attempts by the Maya to adapt to these and other environmental changes. The fourth conceptual model describes a very Late/Terminal Classic, preplanned project on a floodplain. These wetland fields were short-lived, aggraded rapidly but with some reoccupation in the Postclassic. All of these new models display the burgeoning evidence for intricate Maya interactions with wetlands, and the diversity of evidence from the relatively few studies underscores the infancy of our understanding of Maya interaction with tropical wetlands.  相似文献   

Diffuse auroral precipitation in the jovian upper atmosphere and magnetospheric electron flux variability     

Bidushi Bhattacharya  Richard M. Thorne  Krishan K. Khurana 《Icarus》2005,178(2):406-416

The deposition of energetic electrons in Jupiter's upper atmosphere provides a means, via auroral observations, of monitoring electron and plasma wave activity within the magnetosphere. Not only does particle precipitation indicate a potential change in atmospheric chemistry, it allows for the study of episodic, pronounced flux enhancements in the energetic electron population. A study has been made of the effects of such electron injections into the jovian magnetosphere and of their ability to provide the source population for variations in diffuse auroral emissions. To identify the source region of precipitating auroral electrons, we have investigated the pitch-angle distributions of high-resolution Galileo Energetic Particle Detector (EPD) data that indicate strong flux levels near the loss cone. The equatorial source region of precipitating electrons has been determined from the locations of Galileo's in situ measurements by tracing magnetic field lines using the KK97 model. The primary source region for Jupiter's diffuse aurora appears to lie in the magnetic equator at 15-40 RJ, with the predominant contribution to precipitation flux (tens of ergs cm⁻² s⁻¹ sr⁻¹) stemming from <30 RJ. Variability of flux for energetic electrons in this region is also important to the irradiation of surfaces and atmospheres for the Galilean moons: Europa, Ganymede, and Callisto. The average diffuse auroral precipitation flux has been shown to vary by as much as a factor of six at a given radial location. This variability appears to be associated with electron injection events that have been identified in high-resolution Galileo EPD data. These electron flux enhancements are also associated with increased whistler-mode wave activity and magnetic field perturbations, as detected by the Galileo Plasma Wave Subsystem (PWS) and Magnetometer (MAG), respectively. Resonant interactions with the whistler-mode waves cause electron pitch-angle scattering and lead to pitch-angle isotropization and precipitation.  相似文献   

The Spiral Arm Connection of Egret Unidentified Sources     

Torafumi Miyagi  Dipen Bhattacharya  Allen D. Zych 《Astrophysics and Space Science》2005,297(1-4):191-199

Based on a LogN-LogS relation we have shown that the EGRET unidentified source (UnidS) distribution closely follows the Galactic spiral arm structure. This seems to satisfy the hypothesis that the EGRET UnidS arise due to energetic interactions with molecular clouds that reside on the spiral arms. Furthermore, the luminosity distribution of the unidentified sources features a double Gaussian distribution. We suggest that a combined distribution of OB associations, SNR and superbubbles interacting with molecular clouds within the spiral arms are the most likely counterparts of the unidentified sources.  相似文献   

Linking large-parallax Spitzer–CFHT–VLT astrometry of asteroids     

Mikael Granvik  Karri Muinonen  Lynne Jones  Bidushi Bhattacharya  Marco Delbo  Laura Saba  Alberto Cellino  Edward Tedesco  Don Davis  Victoria Meadows 《Icarus》2007,192(2):475-490

We show that the new ephemeris-space multiple-address-comparison (eMAC) method solves asteroid linking problems despite large parallaxes by applying the method to astrometric asteroid observation sets obtained nearly simultaneously with the Spitzer space telescope, the Canada–France–Hawaii Telescope (CFHT), and European Southern Observatory's Very Large Telescope (VLT). For main-belt asteroids, the parallax between Spitzer and the Earth-based telescopes is approximately one degree which is large as compared to a typical parallax for solely Earth-based telescopes in the arcseconds regime. In the eMAC method, we reduce the initially huge amount of possible linkages between observation sets by comparing samples of ephemerides that have been computed separately for all sets at, say, three common dates. If the non-zero ephemeris probability densities overlap at all common dates, we try to find an orbit solution for these so-called trial linkages. If there exists an orbit which reproduces all the astrometric observations assuming predefined observational errors, we call it a linkage. Known asteroids are independently identified among Spitzer, CFHT, and VLT astrometry, and comparing the identified observations to the linkages found shows that the method found all known correct linkages present in the data. In addition, we also found five previously unpublished linkages between Spitzer astrometry and Earth-based astrometry. Based on our simulations, we found virtually all Spitzer-related linkages between two single-night observation sets, and more than 99.4% of linkages between two single-night observation sets obtained by Earth-based observatories. Virtually all correct linkages consisting of at least three single-night sets were also detected. The results show that large-parallax discovery observations made from a spacecraft can be linked to Earth-based follow-up observations to ensure that the objects are not lost. Furthermore, we compute the heliocentric and Spitzer-centric distances as well as the corresponding solar phase angles at the dates of Spitzer observations. Based on comparisons to simulated geocentric observations, we also show that, for typical nearly-simultaneous observations, the parallax reduces the distance uncertainties by several orders of magnitude.  相似文献