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51.
Paul W. Miller Thomas L. Mote Abhishek Kumar Deepak R. Mishra 《Theoretical and Applied Climatology》2020,139(3):861-872
The 2017 and 2018 Atlantic hurricane seasons poignantly illustrated the dangers tropical cyclones pose to US, Central American, and Caribbean coastlines. In particular, Hurricane Maria inflicted widespread damage, including catastrophic defoliation, to Puerto Rico, altering surface heat fluxes and possibly modifying precipitation patterns. This study assesses whether defoliation-driven changes to surface energy fluxes redistribute precipitation in the months following a powerful hurricane landfall. Remote sensing analyses of Maria-related vegetation reduction and recovery from Puerto Rico were adapted to the Georgia coastline. In this novel methodology, the resulting landscape evolution, characterized by an instantaneous vegetation reduction with a gradual recovery, was assimilated into the Weather Research and Forecasting model at a convection-allowing a 3-km grid spacing for the 1 June–1 August 2017 period. The experiment revealed that Maria-scale defoliation reduced precipitation by 14% during the month following landfall within a 50 × 50 km zone containing the hypothetical landfall location. A maximum deficit of 20.0% was reached 4 weeks after landfall. For June 2017, the modeled 14% deficit would have shifted the precipitation total from the 61st to the 47th percentile for years 1981–2016. Meanwhile, precipitation totals were unchanged on the domain scale. The near-landfall drying was also evident in three less-severe defoliation simulations, suggesting that systematic precipitation redistribution near the landfall location is possible following storms considerably weaker than Hurricane Maria. Analyses of the temperature and wind fields suggest that coastal kinematic flow is altered by the introduction of a thermally driven pressure gradient in the defoliated zone. 相似文献
52.
Abhishek Moharana Anurag Mishra Deepak C. Srivastava 《International Journal of Earth Sciences》2013,102(7):1837-1849
The Main Central Thrust demarcates the boundary between the Lesser Himalaya and the Higher Himalaya in the Himalayan orogen. Several definitions of the Main Central Thrust have been proposed since it was originally described as the southern boundary of the crystalline rocks (the Main Central Thrust mass) in the Kumaun-Garhwal Himalaya. The long-held contention that the Munsiari Thrust represents the Main Central Thrust has been negated by recent isotopic studies. One way to define the Main Central Thrust is that it is a ductile shear zone that is delimited by the Munsiari Thrust (MCT-I) in south and the Vaikrita Thrust (MCT-II) in north. The alternative proposition that the Vaikrita Thrust represents the Main Central Thrust is fraught with practical limitations in many parts of the Himalaya, including the study area. In the metamorphic rocks bounded between the Vaikrita Thrust and the Munsiari Thrust, the isoclinal folds of the earliest phase are routinely ascribed to the pre-Himalayan orogeny, whereas all subsequent folding phases are attributed to the Himalayan orogeny. This article elucidates the structural characteristics of the kilometre-thick Munsiari Thrust Zone and revisits the issue of pre-Himalayan orogenic signatures in the thrust zone. With the help of high-resolution field mapping and the analyses of mesoscopic scale structures, we demonstrate that the Munsiari Thrust is a typical fault zone that is made up of a fault core and two damage zones. The fault core traces the boundary between the quartzite and the biotite-gneiss. The damage zones consist of the low-grade metasedimentary rocks in the footwall and the gneiss-migmatite in the hanging wall. The entire fault zone shares an essentially common history of progressive ductile shearing. Successively developed mesoscopic folds trace various stages of progressive ductile shearing in the damage zones. Two recognizable stages of the shearing are represented by the early isoclinal folds and the late kink folds. As the strain during progressive deformation achieved the levels that were too high for accommodation by ductile flow, it was released by development of a tectonic dislocation along a mechanically weak boundary, the Munsiari Thrust. The isoclinal folds and the Munsiari Thrust were developed at different stages of a common progressive deformation during the Himalayan orogeny. Contrary to the popular notion of consistency with respect to orientation, the stretching lineations show large directional variability due to distortion during the late folding. 相似文献
53.
Abhishek Danodia V K Sehgal N R Patel R Dhakar J Mukherjee S K Saha A Senthil Kumar 《Journal of Earth System Science》2017,126(5):69
Amount of available net energy and its partitioning into sensible, latent and soil heat fluxes over an agricultural landscape are critical to improve estimation of evapotranspiration and modelling parse (ecosystem modelling, hydrological and meteorological modelling). Scintillometry is a peculiar and robust methodology to provide structure parameter of refractive index and energy balance. Scintillometer has proven for assessment of sensible and latent heat flux, which is based on the principle of Monin–Obukhov similarity theory. Scintillometer has been installed in the agricultural experimental farm of ICAR-Indian Agricultural Research Institute, New Delhi, with a spatial covering path length of 990 m of irrigated and cultivable agricultural landscape. This paper discusses the patterns of energy flux as diurnal and seasonal basis at scintillometer path which was mainly covered by maize in Kharif and wheat in Rabi season during a crop growing seasons of 2014–2015. The biophysical parameters (leaf area, soil moisture, crop height) were recorded at a temporal resolution of fortnight basis along the path length at usual sampling distance. The Bowen ratio value for both Kharif and Rabi season was 0.76 and 0.88, respectively by scintillometer. Leaf area index had a significantly positive correlation with latent heat flux (\(R^{2} =0.80\)) while a significantly negative correlation with sensible heat flux (\(R^{2}{=}-0.79\)). Soil moisture had a significant negative correlation with sensible heat flux (\(R^{2}{=}-0.68\)). The average evapotranspiration from crop land was \(1.58 ~\hbox {mm d}^{-1}\) and total evapotranspiration was 543 mm over the 12 months study period. This study defines that large aperture scintillometer is robust instrument which can evaluate energy flux over a large area with a long term series time domain. Moreover, further studied should be conducted to use in crop simulation modelling, developing of new model with calibration and validation of remote sensing energy balance algorithm, etc. 相似文献
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While travelling through the subsoil layers, earthquake generated bedrock motions get modified significantly due to local soil and should be quantified using ground response analysis. Present study concentrates on equivalent linear method of site response analysis in SHAKE2000 software. It is a frequency based analysis tool having default frequency set to 15 Hz. While due consideration is given to amplitude, no to very limited information about the frequency content of the input motion to be considered in ground response analysis is available. In the present work, the effect of the maximum frequency of ground motion in site response analysis using SHAKE2000 is examined. Two sets of analyses are carried out in this work based on 30 globally recorded input motions. In the first analyses, input motion up to 15 Hz maximum frequency, which is a default value in SHAKE2000 is considered while second analyses are based on considering each of the 30 input motions up to the Nyquist frequency. Comparing the results from the two sets of analyses highlight that selection of maximum frequency in SHAKE2000 has considerable effect in ground motion amplification at different depths. As a result, even the peak ground acceleration which controls the building behavior and damage scenario, is going to change considerably even in case same input motion is used in the analysis. 相似文献
55.
Abhishek Saha Sohini Ganguly Jyotisankar Ray Nilanjan Chaterjee 《Journal of Earth System Science》2010,119(5):675-699
The Samchampi-Samteran alkaline complex occurs as a plug-like pluton within the Precambrian granite gneisses of Mikir Hills,
Assam, northeastern India and it is genetically related to Sylhet Traps. The intrusive complex is marked by dominant development
of syenite within which ijolitemelteigite suite of rocks is emplaced with an arcuate outcrop pattern. Inliers of alkali pyroxenite
and alkali gabbro occur within this ijolite-melteigite suite of rocks. The pluton is also traversed by younger intrusives
of nepheline syenite and carbonatite. Development of sporadic, lumpy magnetite ore bodies is also recorded within the pluton.
Petrographic details of the constituent lithomembers of the pluton have been presented following standard nomenclatorial rules.
Overall pyroxene compositions range from diopside to aegirine augite while alkali feldspars are typically orthoclase and plagioclase
in syenite corresponds to oligoclase species. Phase chemistry of nepheline is suggestive of Na-rich alkaline character of
the complex. Biotite compositions are typically restricted to a uniform compositional range and they belong to ‘biotite’ field
in the relevant classification scheme. Garnets (developed in syenite and melteigite) typically tend to be Ti-rich andradite,
which on a closer scan can be further designated as melanites. Opaque minerals mostly correspond to magnetite. Use of Lindsley’s
pyroxene thermometric method suggests an equilibration temperature from ∼450°–600°C for melteigite/alkali gabbro and ∼400°C
for syenite. Critical assessment of other thermometric methods reveals a temperature of equilibration of ∼700°–1350°C for
ijolite-melteigite suite of rocks in contrast to a relatively lower equilibration temperature of ∼600°C for syenite. Geobarometric
data based on pyroxene chemistry yield an equilibration pressure of 5.32–7.72 kb for ijolite, melteigite, alkali pyroxenite,
alkali gabbro and nepheline syenite. The dominant syenite member of the intrusive plug records a much higher (∼11 kb) equilibration
pressure indicating a deeper level of intrusion. Major oxide variations of constituent lithomembers with respect to differentiation
index (D.I.) corroborate a normal magmatic differentiation. A prominent role of liquid immiscibility is envisaged from field
geological, petrographic and petrochemical evidences. Tectonic discrimination diagrams involving clinopyroxene chemistry strongly
suggest within plate alkaline affinity for the parental magma which is in conformity with the regional plume tectonics. 相似文献
56.
Abhishek Saha Sohini Ganguly Jyotisankar Ray Avik Dhang 《Journal of the Geological Society of India》2010,76(1):26-32
A new occurrence of (syenite-hosted) Vanadium bearing titaniferous magnetite ore body has been reported from Ganjang (26°09′35″
N: 93°20′ E), Karbi-Anglong, Northeastern India. The magnetite ore bodies have lumpy and sporadic occurrences within the host
syenite pluton intrusive into gneissic country rocks. Ore microscopic studies reveal that magnetite is often associated with
haematite and ilmenite depicting different textural patterns. Critical consideration of several elemental patterns suggests
magmatic differentiation to be main ore-forming process. The ore body is suggested to have been formed as late stage segregation
from a differentiating alkaline magma in a fluid enriched milieu. 相似文献
57.
C K Unnikrishnan John P George Abhishek Lodh Devesh Kumar Maurya Swapan Mallick E N Rajagopal Saji Mohandas 《Journal of Earth System Science》2016,125(5):935-944
Surface level soil moisture from two gridded datasets over India are evaluated in this study. The first one is the UK Met Office (UKMO) soil moisture analysis produced by a land data assimilation system based on Extended Kalman Filter method (EKF), which make use of satellite observation of Advanced Scatterometer (ASCAT) soil wetness index as well as the screen level meteorological observations. Second dataset is a satellite soil moisture product, produced by National Remote Sensing Centre (NRSC) using passive microwave Advanced Microwave Scanning Radiometer 2 measurements. In-situ observations of soil moisture from India Meteorological Department (IMD) are used for the validation of the gridded soil moisture products. The difference between these datasets over India is minimum in the non-monsoon months and over agricultural regions. It is seen that the NRSC data is slightly drier (0.05%) and UKMO soil moisture analysis is relatively wet during southwest monsoon season. Standard AMSR-2 satellite soil moisture product is used to compare the NRSC and UKMO products. The standard AMSR-2 and UKMO values are closer in monsoon season and AMSR-2 soil moisture is higher than UKMO in all seasons. NRSC and AMSR-2 showed a correlation of 0.83 (significant at 0.01 level). The probability distribution of IMD soil moisture observation peaks at 0.25 m3/m3, NRSC at 0.15 m3/m3, AMSR-2 at 0.25 m3/m3 and UKMO at 0.35 m3/m3 during June–September period. Validation results show UKMO analysis has better correlation with in-situ observations compared to the NRSC and AMSR-2 datasets. The seasonal variation in soil moisture is better represented in UKMO analysis. Underestimation of soil moisture during monsoon season over India in NRSC data suggests the necessity of incorporating the actual vegetation for a better soil moisture retrieval using passive microwave sensors. Both products have good agreement over bare soil, shrubs and grassland compared to needle leaf tree, broad leaf tree and urban land cover types. 相似文献
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Sahoo Monica Kumar Abhishek Chalavadi Ganesh Gupta Ambesh Singh Ranjeet K. 《Natural Resources Research》2021,30(5):3643-3658
Natural Resources Research - This study investigated the segregation of organic (maceral) and inorganic (mineral matter or ash) contents of coal in an air stratifier after design modification in... 相似文献