The assessment of aerosol optical properties over Mohal in the northwestern Indian Himalayas using satellite and ground-based measurements and an influence of aerosol transport on aerosol radiative forcing     

Raj Paul Guleria  Jagdish Chandra Kuniyal  Pan Singh Rawat  Nand Lal Sharma  Harinder Kumar Thakur  Pitamber Prasad Dhyani  Mahavir Singh 《Meteorology and Atmospheric Physics》2011,113(3-4):153-169

The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.9oN, 77.12oE) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500?nm, ?ngstr?m exponent and turbidity coefficient are 0.24?±?0.08, 1.02?±?0.34 and 0.13?±?0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550?nm over Mohal within the expected accuracy (???? _p?? ?=?±0.05?±?0.15?? _p?? ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surface-reaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72?K?day^?1, respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.  相似文献   

Correlated projected properties of some triaxial mass models: implications for their intrinsic shapes     

Parijat Thakur  D.K. Chakraborty † 《Monthly notices of the Royal Astronomical Society》2001,328(1):330-338

The projected properties of some triaxial mass models are studied. The models are flattened versions of a set of spherical models. They are constructed by addition of two spherical harmonic terms to a spherical model. The projected properties exhibit strong correlations, when a model with a given set of intrinsic parameters is viewed in all possible orientations. The correlation plots appear to carry signatures of the intrinsic shape of the mass model. Rigorous shape estimates, using Bayesian statistics, yield satisfactory results for the test cases.  相似文献   

Seismotectonics of the 20 October 1991 Uttarkashi earthquake in Garhwal, Himalaya, North India     

V. C. Thakur  Sushil Kumar 《地学学报》1994,6(1):90-94

The 20 October 1991 Uttarkashi earthquake killed over a thousand people and caused extensive damage to property in the Garhwal Himalaya region. The body wave magnitude of the earthquake was 6.6, and the fault plane solution indicates reverse faulting. The hypocenrre was located at a focal depth of about 12 km between the Chail and Jutogh Thrusts, but movement propagated southward along the Jamak–Gangori Fault (JGF) and Dunda fault (DF) which are developed as blind faults related to the growing Uttarkashi antiform.  相似文献   

Geometry of magnetohydrostatic equilbria     

C. Thakur  R. A. Yadav 《Astrophysics and Space Science》1992,192(1):75-78

A geometrical study is made of magnetohydrostatic equilibrium of a perfectly conducting fluid considering magnetic field vector, constant along each current line. We have discussed the geometrical behaviour of Lorentz surfaces, field lines and current lines.Former address: Department of Mathematics, Banaras Hindu University, Varanasi, India.  相似文献   

Active tectonics of Himalayan Frontal Fault system     

V. C. Thakur 《International Journal of Earth Sciences》2013,102(7):1791-1810

In the Sub-Himalayan zone, the frontal Siwalik range abuts against the alluvial plain with an abrupt physiographic break along the Himalayan Frontal Thrust (HFT), defining the present-day tectonic boundary between the Indian plate and the Himalayan orogenic prism. The frontal Siwalik range is characterized by large active anticline structures, which were developed as fault propagation and fault-bend folds in the hanging wall of the HFT. Fault scarps showing surface ruptures and offsets observed in excavated trenches indicate that the HFT is active. South of the HFT, the piedmont zone shows incipient growth of structures, drainage modification, and 2–3 geomorphic depositional surfaces. In the hinterland between the HFT and the MBT, reactivation and out-of-sequence faulting displace Late Quaternary–Holocene sediments. Geodetic measurements across the Himalaya indicate a ~100-km-wide zone, underlain by the Main Himalayan Thrust (MHT), between the HFT and the main microseismicity belt to north is locked. The bulk of shortening, 15–20 mm/year, is consumed aseismically at mid-crustal depth through ductile by creep. Assuming the wedge model, reactivation of the hinterland faults may represent deformation prior to wedge attaining critical taper. The earthquake surface ruptures, ≥240 km in length, interpreted on the Himalayan mountain front through paleoseismology imply reactivation of the HFT and may suggest foreland propagation of the thrust belt.  相似文献   

Geochemistry,petrogenesis and tectonic significance of the basic volcanic units of the Zildat ophiolitic mélange,Indus suture zone,eastern Ladakh (India)     

T. Ahmad  R. Islam  P. P. Khanna  V. C. Thakur 《Geodinamica Acta》2013,26(5):222-233

Abstract

Basic volcanic rocks within the Zildat ophiolitic mélange of Indus suture zone in eastern Ladakh are medium to fine grained with partially preserved primary texture and mineralogy. These rocks are predominantly alkaline basalt with high Nb/Y and enriched incompatible trace element characteristics, similar to those of the oceanic island basalt (OIB). The minor sub-alkaline basaltic rocks resemble N-type mid ocean ridge basalt (N-MORB) but with much lower abundances of incompatible trace element including REE. The alkaline rocks probably generated through variable, but low degrees of partial melting of enriched mantle source and evolved through high pressure olivine and clinopyroxene fractionation. Low pressure plagioclase and Fe- Ti oxide do not appear to be major fractionating phases. Limited data on the sub-alkaline rocks suggest that their parental melts were derived from mantle sources some what similar to that of N- MORB. Significant role of added cumulates of olivine, clinopyroxene and Fe- Ti oxides is also indicated in their genesis. Ophiolitic mélanges all along the Indus suture zone appear to have formed due to the accumulation of mélange material in the upper part of the subduction zone where they suffered glaucophanitic (blueschist) metamorphism and retrograded partially to greenschist grade as these were subsequently obducted to its present position probably during the Cenozoic Himalayan orogeny due to collision of Indian and Eurasian plates.  相似文献   

River bank erosion hazard study of river Ganga,upstream of Farakka barrage using remote sensing and GIS   总被引：1，自引：0，他引：1  

Praveen K. Thakur  Chalantika Laha  S. P. Aggarwal 《Natural Hazards》2012,61(3):967-987

This study has been carried out to analyze and report the river bank erosion hazard due to morphometric change of the Ganga River (also called Ganges in English) in the upstream of Farakka Barrage up to Rajmahal. Morphometric parameters, such as, Sinuosity, Braidedness Index, and percentage of the island area to the total river reach area were measured for the year of 1955, 1977, 1990, 2001, 2003, and 2005 from LANDSAT and IRS satellite images. The analysis shows that there is a drastic increase in all of those parameters over the period of time. This study has found that bank failure is because of certain factors like soil stratification of the river bank, presence of hard rocky area (Rajmahal), high load of sediment and difficulty of dredging and construction of Farakka Barrage as an obstruction to the natural river flow. For the increasing sinuosity, the river has been engulfing the large areas of left bank every year. The victims are mostly Manikchak and Kaliachak-II blocks of Malda district, with a loss of around 1,670 ha agricultural land since 1977. Temporal shift measurements for the river reach between Farakka and Rajmahal has been done with help of 22 cross-sections in this reach. Erosion impact area has also been estimated to emphasize the devastating nature of the hazard.  相似文献   

Abundance ratios in quasi-stellar objects     

R. K. Thakur  P. K. Mishra 《Astrophysics and Space Science》1977,51(2):249-264

Relative abundances of carbon and aluminium with respect to silicon have been calculated in the QSOs PHL957, PKS0237-23, 1331+170, 3C191 and M132. Relative abundance of Fe with respect to Mg has been also calculated in the QSOs 1331+170 and PHL938. The ratiosN(C)/N(Si),N(Al)/N(Si) andN(Fe)/N(Mg) in QSOs considered as a class are (5.5±1.6), (0.13±0.03) and (2.6±1.2), respectively.The ratioN(C)/N(Si) shows a mild trend of increase with decreasing emission redshift. This suggests the possibility that the QSOs might be evolving chemically.  相似文献   

Active faulting south of the Himalayan Front: Establishing a new plate boundary   总被引：1，自引：0，他引：1  

Robert S. Yeats  V.C. Thakur   《Tectonophysics》2008,453(1-4):63

New tectonic uplifts south of the Salt Range Thrust and Himalayan Front Thrust (HFT) represent an outward step of the plate boundary from the principal tectonic displacement zone into the Indo-Gangetic Plain. In Pakistan, the Lilla Anticline deforms fine-grained overbank deposits of the Jhelum River floodplain 15 km south of the Salt Range. The anticline is overpressured in Eocambrian non-marine strata. In northwest India south of Dehra Dun, the Piedmont Fault (PF) lies 15 km south of the HFT. Coalescing fans derived from the Himalaya form a piedmont (Old Piedmont Zone) 15–20 km wide east of the Yamuna River. This zone is uplifted as much as 15–20 m near the PF, and bedding is tilted 5–7° northeast. Holocene thermoluminescence-optically-stimulated luminescence dates for sediments in the Old Piedmont Zone suggest that the uplift rate might be as high as several mm/a. The Old Piedmont Zone is traced northwest 200 km and southeast another 200 km to the Nepal border. These structures, analogous to protothrusts in subduction zones, indicate that the Himalayan plate boundary is not a single structure but a series of structures across strike, including reactivated parts of the Main Boundary Thrust north of the range front, the HFT sensu stricto, and stepout structures on the Indo-Gangetic Plain. Displacement rates on all these structures must be added to determine the local India-Himalaya convergence rate.  相似文献   

The origin of the Big-Bang     

R. K. Thakur 《Astrophysics and Space Science》1992,190(2):281-292

Within the framework of FLRW cosmology withk=+1 a singularity free model of the Universe is proposed which readily accounts for the origin of the Big-Bang and for the preponderance of matter over anti-matter. It is also free from the problems of accounting for the observed large-scale homogeneity and isotropy of the Universe as well as from the problems of horizon and flatness. It is pointed out that the collapsing universe might have acted as an ultra-high energy particle accelerator. In the collapsing phase of the Universe, when the interparticle distances10^–16 cm, the electromagnetic and weak interactions might have unified into electroweak interaction and as the collapse proceeded further the entire matter in the Universe might have been converted into quark-gluon plasma permeated by leptons. The gravitational energy released during the collapse might have been locked in this plasma. Ass approached 10^–28 cm, grand unification of electroweak and strong interactions might have occurred. It is also suggested that, with further collapse, whens<10^–33 cm super-symmetry (SUSY)—i.e., the unification of all the four interactions (viz., electromagnetic, weak, strong, and gravitational) might have occurred. During this process gravitinos, the supersymmetric partners of graviton might have been produced. As a result of the exchange of a pair of virtual gravitinos between two particles an ultra-strong repulsive force between them might have been generated. Due to this ultra-strong repulsive interaction between particles the motion of the Universe might have been reversed, i.e., the Universe might have started expanding. During expansion, whens10^–28 cm, SUSY might have broken down spontaneously toSU ₅ and gravity. Ass increased from 10^–28 to 10^–16 cm, the gravitational energy locked in the quark-gluon plasma might have been released with a gigantic explosion, the so-called Big-Bang. It is estimated here that during this Big-Bang more than 10⁸² GeV of energy might have been released. Whens10^–16 cm,SU ₅ might have broken down spontaneously toSU ₃ andU ₁. Expansion beyond this stage might have occurred in the manner described by the standard cosmology. It is further suggested that in due course of time expansion will be followed by contraction and the cycle of contraction-expansion-contraction will be repeated ad infinitum.  相似文献