Coastal circulation along the central west coast of India during cyclone Phyan: measurements and numerical simulations     

K. Vinod Kumar  V. M. Aboobacker  P. P. Saheed  P. Vethamony 《Natural Hazards》2012,64(1):259-271

Measurements and numerical simulations carried out off Mumbai coast for the period 22 October?C22 November 2009 showed significant variations in water level and currents during cyclone Phyan. Changes in the meridional component of the current velocity were found to be highly significant during Phyan. The strong southward flow due to the cyclone resulted in a complete nullification of a flood current and continued the net flow towards south for approximately 18?h. This enhanced the ebb flow by about 0.12?m/s off Worli and 0.16?m/s off Satpati. The shift in the cyclone generated currents towards north resulted in an enhancement of flood current by 0.3?m/s off Worli and 0.2?m/s off Satpati. During the first 7?h of Phyan, a strong current system associated with an anti-cyclonic eddy was formed off Mangalore, which propagated towards north up to Ratnagiri and disappeared while the cyclone entered the land. Water level variations of 0.38 and 0.44?m were observed due to Phyan off Worli and Satpati, respectively. Positive and negative surges, that is, a fall in water level up to ?20?cm and a rise up to 20?cm, were observed during Phyan and these were associated with shift in the wind direction.  相似文献   

One-Dimensional Consolidation of Sedimented Stowed Pond Ash     

Devi Prasad Mishra  Samir Kumar Das 《Geotechnical and Geological Engineering》2012,30(4):685-695

Use of fly ash locked in the ash ponds in geotechnical applications such as stowing or backfilling of the mines is an attractive alternative to solve the disposal problem. Before it is used as a stowing or backfilling material, the response of the fly ash?to imposed load must be determined in order to assess its load taking ability. The present study examines the effect of time and incremental load on the consolidation characteristics of the sedimented stowed pond ash using a fixed ring consolidometer. The important parameters, viz. rate of settlement, consolidation coefficients and void ratio, etc. of the hydraulically stowed pond ash collected after 7, 14, 21, 28 and 35?days of stowing under step incremental loads are determined. The study revealed that 60.42–84.87% settlement of the sedimented stowed pond ash takes place in the initial 1?min of the loading. In addition, it is observed that the coefficient of consolidation of the sedimented stowed pond ash, which varies in the range of 0.0195–0.1882?cm²/min, is comparatively low and decreases with the increment of applied load and time. This indicates that the structures lying above the stowed pond ash mass will undergo gradual settling and not suffer large deformation.  相似文献   

Wet and dry spell analysis of Global Climate Model-generated precipitation using power laws and wavelet transforms   总被引：2，自引：2，他引：0  

Ashok K. Mishra  Mehmet ?zger  Vijay P. Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(4):517-535

Climate model simulations for the twenty-first century point toward changing characteristics of precipitation. This paper investigates the impact of climate change on precipitation in the Kansabati River basin in India. A downscaling method, based on Bayesian Neural Network (BNN), is applied to project precipitation generated from six Global Climate Models (GCMs) using two scenarios (A2 and B2). Wet and dry spell properties of monthly precipitation series at five meteorologic stations in the Kansabati basin are examined by plotting successive wet and dry durations (in months) against their number of occurrences on a double-logarithmic paper. Straight-line relationships on such graphs show that power laws govern the pattern of successive persistent wet and dry monthly spells. Comparison of power-law behaviors provides useful interpretation about the temporal precipitation pattern. The impact of low-frequency precipitation variability on the characteristics of wet and dry spells is also evaluated using continuous wavelet transforms. It is found that inter-annual cycles play an important role in the formation of wet and dry spells.  相似文献   

Geochemical signatures for the grain size variation in the siliciclastics of Kaimur Group,Vindhyan Supergroup from Markundi ghat,Sonbhadra district, (U.P.), India     

M. Mishra  S. Sen 《Geochemistry International》2011,49(3):274-290

The chemical composition of siliciclastics from Mesoproterozoic Kaimur Group, Vindhyan Supergroup have been investigated to determine and appraise the influence of the weathering, hydraulic sorting and recycling processes upon source rock signature. The studies pertaining to the relationship between major, trace and REE and the grain size variation were carried out along Markundi ghat section, Sonbhadra district, Son valley. Upper Kaimur Group has been divided into three principal formations-the uppermost-Dhandraul quartzites, Scarp sandstone and Bijaigarh shales. Petrographically, they range from quartz arenite, sublitharenite, subfeldspathic arenite to pyritiferous shale. The elemental enrichment, except for SiO₂, is in the following order-Bijaigarh Shale > Scarp Sandstone ≫ Dhandraul Sandstone.  相似文献   

Paleoproterozoic quartz-pebble conglomerate type uranium mineralisation in Mankarhachua area,Angul district,Orissa     

Kalyan Chakrabarti  N. R. R. Ecka  B. Mishra  P. V. Ramesh Babu  P. S. Parihar 《Journal of the Geological Society of India》2011,77(5):443-449

Ground Radiometric survey of Paleoproterozoic pyritiferous quartz-pebble conglomerate (QPC) occurring to the north of Pallahara area led to the discovery of a QPC type uranium mineralisation near Mankarhachua village. Significant radioactivity is recorded in three sub-parallel uraniferous QPC horizons with metamorphosed pebbly to medium grained recrystallised massive sandstones. Detrital grains of uranothorite, thorite, radioactive allanite, monazite, zircon, minute uraninite grains in carbonaceous matter and thucolite contributes to the radioactive phases present in QPC matrix. Adsorbed U on limonite and goethite, secondary uranyl minerals in matrix, along bedding planes and fractures are commonly observed. This discovery has opened up a new horizon for future exploration for QPC type uranium mineralization in the area. The paper presents observations on geology, radioactivity, petrological and geochemical nature of the uraniferous QPC horizons.  相似文献   

Snow cover depletion under changed climate with the help of remote sensing and temperature data   总被引：1，自引：1，他引：0  

Sanjay K. Jain  L. N. Thakural  R. D. Singh  A. K. Lohani  S. K. Mishra 《Natural Hazards》2011,58(3):891-904

Snow cover depletion curve (SDC) is one of the important variables in snow hydrological applications, and these curves are very much required for snowmelt runoff modeling in a snowfed catchment. Remote sensing is an important source of snow cover area which is used for preparation of SDC. Snow cover maps produced by Moderate Resolution Imaging Spectroradiometer (MODIS) satellites are one of the best source of satellite-based snow cover area at a regular interval. Therefore, in this study, snow cover maps have been prepared for the years 2000?C2005 using MODIS data. The study area chosen viz. Beas basin up to Pandoh dam falls in western Himalayan region. For snowmelt runoff modeling, catchment is divided into number of elevation zones and SDC is required for each zone. When sufficient satellite data are not available due to cloud cover or due to some other reasons, then SDC can to be generated using temperature data. Under changed climate conditions also, modified SDC is required. Therefore, to have SDC under such situations, a relationship between snow cover area and cumulative mean temperature has been developed for each zone of the catchment. This procedure of having snow cover maps has two main purposes. First, it could potentially be used to generate snow cover maps when cloud-free satellite data are not available. Second, it can be used to generate snow-covered area in a new climate to see the impact of climate change on snowmelt runoff studies.  相似文献   

Geodynamics of NW India: Subduction, lithospheric flexure, ridges and seismicity     

M. Ravi Kumar  D. C. Mishra  B. Singh  D. Ch. Venkat Raju  M. Singh 《Journal of the Geological Society of India》2013,81(1):61-78

Spectral analysis of digital data of the Bouguer anomaly map of NW India suggests maximum depth of causative sources as 134 km that represents the regional field and coincides with the upwarped lithosphere — asthenosphere boundary as inferred from seismic tomography. This upwarping of the Indian plate in this section is related to the lithospheric flexure due to its down thrusting along the Himalayan front. The other causative layers are located at depths of 33, 17, and 6 km indicating depth to the sources along the Moho, lower crust and the basement under Ganga foredeep, the former two also appear to be upwarped as crustal bulge with respect to their depths in adjoining sections. The gravity and the geoid anomaly maps of the NW India provide two specific trends, NW-SE and NE-SW oriented highs due to the lithospheric flexure along the NW Himalayan fold belt in the north and the Western fold belt (Kirthar -Sulaiman ranges, Pakistan) and the Aravalli Delhi Fold Belt (ADFB) in the west, respectively. The lithospheric flexures also manifest them self as crustal bulge and shallow basement ridges such as Delhi — Lahore — Sagodha ridge and Jaisalmer — Ganganagar ridge. There are other NE-SW oriented gravity and geoid highs that may be related to thermal events such as plumes that affected this region. The ADFB and its margin faults extend through Ganga basin and intersect the NW Himalayan front in the Nahan salient and the Dehradun reentrant that are more seismogenic. Similarly, the extension of NE-SW oriented gravity highs associated with Jaisalmer — Ganganagar flexure and ridge towards the Himalayan front meets the gravity highs of the Kangra reentrant that is also seismogenic and experienced a 7.8 magnitude earthquake in 1905. Even parts of the lithospheric flexure and related basement ridge of Delhi — Lahore — Sargodha show more seismic activity in its western part and around Delhi as compared to other parts. The geoid highs over the Jaisalmer — Ganganagar ridge passes through Kachchh rift and connects it to plate boundaries towards the SW (Murray ridge) and NW (Kirthar range) that makes the Kachchh as a part of a diffused plate boundary, which, is one of the most seismogenic regions with large scale mafic intrusive that is supported from 3-D seismic tomography. The modeling of regional gravity field along a profile, Ganganagar — Chandigarh extended beyond the Main Central Thrust (MCT) constrained from the various seismic studies across different parts of the Himalaya suggests crustal thickening from 35-36 km under plains up to ～56 km under the MCT for a density of 3.1 g/cm³ and 3.25 g/cm³ of the lower most crust and the upper mantle, respectively. An upwarping of ～3 km in the Moho, crust and basement south of the Himalayan frontal thrusts is noticed due to the lithospheric flexure. High density for the lower most crust indicates partial eclogitization that releases copious fluid that may cause reduction of density in the upper mantle due to sepentinization (3.25 g/cm³). It has also been reported from some other sections of Himalaya. Modeling of the residual gravity and magnetic fields along the same profile suggest gravity highs and lows of NW India to be caused by basement ridges and depressions, respectively. Basement also shows high susceptibility indicating their association with mafic rocks. High density and high magnetization rocks in the basement north of Chandigarh may represent part of the ADFB extending to the Himalayan front primarily in the Nahan salient. The Nahan salient shows a basement uplift of ～ 2 km that appears to have diverted courses of major rivers on either sides of it. The shallow crustal model has also delineated major Himalayan thrusts that merge subsurface into the Main Himalayan Thrust (MHT), which, is a decollment plane.  相似文献   

Detrital iron-ore deposits in the Iron Ore Group of rocks,northern Orissa,eastern India     

B. K. Mohapatra  P. P. Singh  P. Mishra  K. Mahant 《Australian Journal of Earth Sciences》2013,60(8):1139-1152

Detrital iron deposits (DID) are located adjacent to the Precambrian bedded iron deposit (BID) of Joda near the eastern limb of the horseshoe-shaped synclinorium, in the Bonai–Keonjhar belt of Orissa. The detrital ores overlie the Dhanjori Group sandstone as two isolated orebodies (Chamakpur and Inganjharan) near the eastern and western banks of the Baitarani River, respectively. The DID occur as pebble/cobble conglomerates containing iron-rich clasts cemented by goethite. Mineralogy, chemistry and lamination of these clasts are similar to that found in the nearby BID ores. Enrichment of trace and rare-earth elements in the DID relative to the BID is attributed to their concentration during the precipitation of cementing material. The detrital iron orebodies formed when Proterozoic weathering processes eroded pre-existing BID outcrops located on the Joda Ranges, and the resulting detritus accumulated in the paleochannels. In situ dissolution in association with abundant organic material produced Fe-saturated groundwater, which re-precipitated as goethite within the aggraded channel to cement the detritals. Growth of microplaty hematite in the goethite matrix suggests some level of subsequent burial metamorphism.  相似文献   

Modulational instability of ion-acoustic waves in electron–positron–ion plasmas     

J. K. Chawla  M. K. Mishra  R. S. Tiwari 《Astrophysics and Space Science》2013,347(2):283-292

The stability of modulation of ion-acoustic waves in a collisionless electron–positron–ion plasma with warm adiabatic ions is studied. Using the Krylov–Bogoliubov–Mitropolosky (KBM) perturbation technique a nonlinear Schrödinger equation governing the slow modulation of the wave amplitude is derived for the system. It is found that for given set of parameters having finite ion temperature ratio (T _i /T _e ) the waves are unstable for the values of k lying in the range k _min<k<k _max. On increasing the ion temperature ratio (T _i /T _e ), it is found that k _min and k _max, both decreases and product PQ increases. The range of unstable region shifts towards the small wave number k, as temperature ratio (T _i /T _e ) increases. The positron concentration and temperature ratio of positron to electron, change the unstable region slightly. As positron concentration increases both k _min and k _max for modulational instability increases and maximum value of the product PQ shifts towards the larger value of k.  相似文献   

Five dimensional bulk viscous cosmological model with wet dark fluid in general relativity     

G. C. Samanta  S. Dhal  B. Mishra 《Astrophysics and Space Science》2013,346(1):233-236

In this paper, we have constructed a five dimensional LRS Bianchi type I cosmological model with wet dark fluid (WDF) in general relativity with the matter field described as bulk viscosity. It is found that in presence of bulk viscosity an inflationary effective stiff fluid cosmological model is obtained, whereas in absence of bulk viscosity the wet dark fluid degenerate to stiff fluid. Some physical and geometrical properties of the model are also discussed.  相似文献