Land use mapping of kandi belt of jammu region     

Vijay?Kumar  S.?P.?Rai  D.?S.?RathoreEmail author 《Journal of the Indian Society of Remote Sensing》2004,32(4):323-328

Digital image processing on IRS-1C-LISS-III data acquired on October 13, 1998 has been carried out to map the land use classes in part of the Kandi belt, the submontane tract lying in the Outer Himalaya of Jammu region of Jammu and Kashmir. Supervised classification has been combined with rule-based classification to delineate various land use classes. The various categories of land use in the area recognized are forest, agriculture, riverbed, urban, fallow, wasteland and water. Forest is dominant along the upper boundary of the Kandi belt (along Siwalik) and on ridges, whereas, agriculture land is mainly along the lower boundary (along Sirowal) of the study area.  相似文献   

Ocean Model Simulation of Southern Indian Ocean Surface Currents   总被引：1，自引：0，他引：1  

Anshu Prakash Mishra  S. Rai  A. C. Pandey 《Marine Geodesy》2007,30(4):345-354

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N-60°S and 30°E-120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.  相似文献   

Geo-spatial analysis of temporal trends of temperature and its extremes over India using daily gridded (1°×1°) temperature data of 1969–2005     

Abhishek?ChakrabortyEmail author  M?V?R?Seshasai  S?V?C?Kameswara?Rao  V?K?Dadhwal 《Theoretical and Applied Climatology》2017,130(1-2):133-149

Daily gridded (1°×1°) temperature data (1969–2005) were used to detect spatial patterns of temporal trends of maximum and minimum temperature (monthly and seasonal), growing degree days (GDDs) over the crop-growing season (kharif, rabi, and zaid) and annual frequencies of temperature extremes over India. The direction and magnitude of trends, at each grid level, were estimated using the Mann–Kendall statistics (α = 0.05) and further assessed at the homogeneous temperature regions using a field significance test (α=0.05). General warming trends were observed over India with considerable variations in direction and magnitude over space and time. The spatial extent and the magnitude of the increasing trends of minimum temperature (0.02–0.04 °C year^?1) were found to be higher than that of maximum temperature (0.01–0.02 °C year^?1) during winter and pre-monsoon seasons. Significant negative trends of minimum temperature were found over eastern India during the monsoon months. Such trends were also observed for the maximum temperature over northern and eastern parts, particularly in the winter month of January. The general warming patterns also changed the thermal environment of the crop-growing season causing significant increase in GDDs during kharif and rabi seasons across India. The warming climate has also caused significant increase in occurrences of hot extremes such as hot days and hot nights, and significant decrease in cold extremes such as cold days and cold nights.  相似文献   

On the large-scale diffuse magnetic field of the sun     

Mausumi Dikpati  Arnab Rai Choudhuri 《Solar physics》1995,161(1):9-27

Although the sunspots migrate towards the equator, the large-scale weak diffuse magnetic fields of the Sun migrate poleward with the solar cycle, the polar field reversing at the time of the sunspot maxima. We apply the vector model of Dikpati and Choudhuri (1994, Paper I) to fit these observations. The dynamo layer at the base of the convection zone is taken to be the source of the diffuse field, which is then evolved in the convection zone subject to meridional circulation and turbulent diffusion. We find that the longitudinally averaged observational data can be fitted reasonably well both for positive and negative values of the-effect by adjusting the subsurface meridional flow suitably. The model will be extended in a future paper to include the decay of active regions as an extra source of the diffuse field, which may be necessary to explain the probable phase lag betweenB _r andB at lower latitudes.  相似文献   

Assessing crop water stress during late kharif season using Normalized Diurnal Difference Vegetation Water Content (nddVWC) of Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E)     

Abhishek Chakraborty  M. V. R. Seshasai  V. K. Dadhwal 《Natural Hazards》2016,84(1):533-549

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Earthquake hazard in Northeast India — A seismic microzonation approach with typical case studies from Sikkim Himalaya and Guwahati city     

Sankar Kumar Nath  Kiran Kumar Singh Thingbaijam  Abhishek Raj 《Journal of Earth System Science》2008,117(2):809-831

A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly alluvial basin respectively. The estimated maximum earthquakes in the underlying seismic source zones, demarcated in the broad northeast Indian region, implicates scenario earthquakes of M _W 8.3 and 8.7 to the respective study regions for deterministic seismic hazard assessments. The microzonation approach as undertaken in the present analyses involves multi-criteria seismic hazard evaluation through thematic integration of contributing factors. The geomorphological themes for Sikkim Himalaya include surface geology, soil cover, slope, rock outcrop and landslide integrated to achieve geological hazard distribution. Seismological themes, namely surface consistent peak ground acceleration and predominant frequency were, thereafter, overlaid on and added with the geological hazard distribution to obtain the seismic hazard microzonation map of the Sikkim Himalaya. On the other hand, the microzonation study of Guwahati city accounts for eight themes — geological and geomorphological, basement or bedrock, landuse, landslide, factor of safety for soil stability, shear wave velocity, predominant frequency, and surface consistent peak ground acceleration. The five broad qualitative hazard classifications — ‘low’, ‘moderate’, ‘high’, ‘moderate high’ and ‘very high’ could be applied in both the cases, albeit with different implications to peak ground acceleration variations. These developed hazard maps offer better representation of the local specific seismic hazard variation in the terrain.  相似文献   

Earthquake hazard zonation of Sikkim Himalaya using a GIS platform   总被引：2，自引：1，他引：1  

Indrajit Pal  Sankar Kumar Nath  Khemraj Shukla  Dilip Kumar Pal  Abhishek Raj  K. K. S. Thingbaijam  B. K. Bansal 《Natural Hazards》2008,45(3):333-377

An earthquake hazard zonation map of Sikkim Himalaya is prepared using eight thematic layers namely Geology (GE), Soil Site Class (SO), Slope (SL), Landslide (LS), Rock Outcrop (RO), Frequency–Wavenumber (F–K) simulated Peak Ground Acceleration (PGA), Predominant Frequency (PF), and Site Response (SR) at predominant frequencies using Geographic Information System (GIS). This necessitates a large scale seismicity analysis for seismic source zone classification and estimation of maximum earthquake magnitude or maximum credible earthquake to be used as a scenario earthquake for a deterministic or quasi-probabilistic seismic scenario generation. The International Seismological Center (ISC) and Global Centroid Moment Tensor (GCMT) catalogues have been used in the present analysis. Combining b-value, fractal correlation dimension (Dc) of the epicenters and the underlying tectonic framework, four seismic source zones are classified in the northeast Indian region. Maximum Earthquake of M _W 8.3 is estimated for the Eastern Himalayan Zone (EHZ) and is used to generate the seismic scenario of the region. The Geohazard map is obtained through the integration of the geological and geomorphological themes namely GE, SO, SL, LS, and RO following a pair-wise comparison in an Analytical Hierarchy Process (AHP). Detail analysis of SR at all the recording stations by receiver function technique is performed using 80 significant events recorded by the Sikkim Strong Motion Array (SSMA). The ground motion synthesis is performed using F–K integration and the corresponding PGA has been estimated using random vibration theory (RVT). Testing for earthquakes of magnitude greater than M _W 5, a few cases presented here, establishes the efficacy and robustness of the F–K simulation algorithm. The geohazard coverage is overlaid and sequentially integrated with PGA, PF, and SR vector layers, in order to evolve the ultimate earthquake hazard microzonation coverage of the territory. Earthquake Hazard Index (EHI) quantitatively classifies the terrain into six hazard levels, while five classes could be identified following the Bureau of Indian Standards (BIS) PGA nomenclature for the seismic zonation of India. EHI is found to vary between 0.15 to 0.83 quantitatively classifying the terrain into six hazard levels as “Low” corresponding to BIS Zone II, “Moderate” corresponding to BIS Zone III, “Moderately High” belonging to BIS Zone IV, “High” corresponding to BIS Zone V(A), “Very High” and “Severe” with new BIS zones to Zone V(B) and V(C) respectively.  相似文献   

Recent seismicity in Northeast India and its adjoining region     

Kiran Kumar Singh Thingbaijam  Sankar Kumar Nath  Abhimanyu Yadav  Abhishek Raj  M. Yanger Walling  William Kumar Mohanty 《Journal of Seismology》2008,12(1):107-123

Recent seismicity in the northeast India and its adjoining region exhibits different earthquake mechanisms – predominantly thrust faulting on the eastern boundary, normal faulting in the upper Himalaya, and strike slip in the remaining areas. A homogenized catalogue in moment magnitude, M _W, covering a period from 1906 to 2006 is derived from International Seismological Center (ISC) catalogue, and Global Centroid Moment Tensor (GCMT) database. Owing to significant and stable earthquake recordings as seen from 1964 onwards, the seismicity in the region is analyzed for the period with spatial distribution of magnitude of completeness m _t, b value, a value, and correlation fractal dimension D _C. The estimated value of m _t is found to vary between 4.0 and 4.8. The a value is seen to vary from 4.47 to 8.59 while b value ranges from 0.61 to 1.36. Thrust zones are seen to exhibit predominantly lower b value distribution while strike-slip and normal faulting regimes are associated with moderate to higher b value distribution. D _C is found to vary from 0.70 to 1.66. Although the correlation between spatial distribution of b value and D _C is seen predominantly negative, positive correlations can also be observed in some parts of this territory. A major observation is the strikingly negative correlation with low b value in the eastern boundary thrust region implying a possible case of extending asperity. Incidentally, application of box counting method on fault segments of the study region indicates comparatively higher fractal dimension, D, suggesting an inclination towards a planar geometrical coverage in the 2D spatial extent. Finally, four broad seismic source zones are demarcated based on the estimated spatial seismicity patterns in collaboration with the underlying active fault networks. The present work appraises the seismicity scenario in fulfillment of a basic groundwork for seismic hazard assessment in this earthquake province of the country.  相似文献   

Using fluorescein and bromide tracers to investigate the role of baseflow in a small suburban watershed in Iowa,USA          下载免费PDF全文

S. Rai  M. Z. Iqbal 《水文研究》2015,29(2):173-186

Fluorescein and bromide tracers were used to study baseflow mechanisms of a small suburban watershed in northeast Iowa, USA. The tracers were applied to ten injection holes ranging from 1.3 to 3.0 ft in depth in two phases. Separately, two PVC wells (15 and 16 ft deep) were used to investigate tracer movement in a deeper flow system. Over 30 days of phase 1, none of the tracers was detected in the creek water. In phase 2, fluorescein was irregularly detected in the creek at two sites, whereas bromide was detected at one site only. Meanwhile, soil analysis detected measurable diffusion of bromide and fluorescein at four sites. At each of these sites, the tracer was found to be diffusing toward the creek. None of the tracers applied to the deeper PVC wells showed any movement toward the creek over 1 month of continuous sampling. Isotopic composition of water samples varied spatially as well as temporally going from the deep well (δ¹⁸O = ?8.89‰) to the injection holes (average δ¹⁸O = ?8.42‰), to the creek (average δ¹⁸O = ?7.86‰), and further to the rain samples (average δ¹⁸O = ?4.68‰). The analytical error margin is ±0.09‰. Samples from the injection holes were generally heavier than the deep well sample and lighter than the creek samples, indicating that there was no significant connection between the surface and the subsurface systems. Furthermore, the sporadic appearance of bromide and fluorescein both spatially and temporally points to the fact that baseflow does not constitute a significant part of the area's stream discharge. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

On the coalescence of twisted flux tubes     

Arnab Rai Choudhuri 《地球物理与天体物理流体动力学》2013,107(3-4):261-291

Abstract

We study the problem of the coalescence of twisted flux tubes by assuming that the azimuthal field lines reconnect at a current sheet during the coalescence process and everywhere else the magnetic field is frozen in the fluid. We derive relations connecting the topology of the coalesced flux tube with the topologies of the initial flux tubes, and then obtain a structure equation for calculating the field configuration of the coalesced flux tube from the given topology. Some solutions for the two extreme cases of low-β plasma and high-β plasma are discussed. The coalesced flux tube has less twist than the initial flux tube. Magnetic helicity is found to be exactly conserved during the coalescence, but the assumptions in the model put a constraint on the energy dissipation so that we do not get a relaxation to the minimum-energy Taylor state in the low-β case. It is pointed out that the structure equation connecting the topology and the equilibrium configuration is quite general and can be of use in many two-dimensional flux tube problems.  相似文献