• Volume 118, Issue 5

      October 2009,   pages  413-617

    • Impact of vegetation on the simulation of seasonal monsoon rainfall over the Indian subcontinent using a regional model

      Surya K Dutta Someshwar Das S C Kar U C Mohanty P C Joshi

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      The change in the type of vegetation fraction can induce major changes in the local effects such as local evaporation,surface radiation,etc.,that in turn induces changes in the model simulated outputs.The present study deals with the effects of vegetation in climate modeling over the Indian region using the MM5 mesoscale model.The main objective of the present study is to investigate the impact of vegetation dataset derived from SPOT satellite by ISRO (Indian Space Research Organization)versus that of USGS (United States Geological Survey)vegetation dataset on the simulation of the Indian summer monsoon.The present study has been conducted for five monsoon seasons (1998 –2002),giving emphasis over the two contrasting southwest monsoon seasons of 1998 (normal)and 2002 (deficient).

      The study reveals mixed results on the impact of vegetation datasets generated by ISRO and USGS on the simulations of the monsoon.Results indicate that the ISRO data has a positive impact on the simulations of the monsoon over northeastern India and along the western coast.The MM5- USGS has greater tendency of overestimation of rainfall.It has higher standard deviation indicating that it induces a dispersive effect on the rainfall simulation.Among the five years of study,it is seen that the RMSE of July and JJAS (June –July –August –September)for All India Rainfall is mostly lower for MM5-ISRO.Also,the bias of July and JJAS rainfall is mostly closer to unity for MM5-ISRO.The wind fields at 850 hPa and 200 hPa are also better simulated by MM5 using ISRO vegetation.The synoptic features like Somali jet and Tibetan anticyclone are simulated closer to the veri fication analysis by ISRO vegetation.The 2 m air temperature is also better simulated by ISRO vegetation over the northeastern India,showing greater spatial variability over the region. However,the JJAS total rainfall over north India and Deccan coast is better simulated using the USGS vegetation.Sensible heat flux over north-west India is also better simulated by MM5-USGS.

    • The interaction of large scale and mesoscale environment leading to formation of intense thunderstorms over Kolkata. Part I: Doppler radar and satellite observations

      P Mukhopadhyay M Mahakur H A K Singh

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      The weather systems that predominantly affect the eastern and northeastern parts of India during the pre-monsoon summer months (March,April and May)are severe thunderstorms,known as Nor ’westers.The storms derive their names from the fact that they frequently strike cities and towns in the southern part of West Bengal in the afternoon from the north-west direction while traveling far from its place of genesis over the Bihar plateau.The storms are devastating in nature particularly due to strong (gusty)winds,heavy rains and hails associated with it.Although these storms are well known for its power of causing damages,studies on them are relatively few due to their small size and sparse network of observations.To address this important issue,the evolution of two Nor ’westers of 12 March and 22 May 2003 over Kolkata is studied in detail in this paper using hourly Doppler weather radar (DWR)observations and high resolution Meteosat-5 imageries.In addition,supporting meteorological reports are used to find the large scale conditions that influence the moisture convergence and vertical wind shear.The genesis of both the storms is found to be over Bihar –Jharkhand region and beyond the range of the DWR.The satellite observations are found to be useful in identifying the location and initiation of the storms.The movements of the storms are captured by the DWR estimated vertical cross-section of reflectivities.The Doppler estimate shows that the 12 March storm had a vertical extent of about 10 –12 km at the time of maturity and that of 22 May reaching up to 18 km signifying deep convection associated with these events.The genesis, maturity and dissipation are well brought out by the hourly DWR and satellite imageries.The DWR observations suggest that the systems move at a speed of 20 –25 m/s.The DWR estimated precipitation shows a detailed spatial distribution around Kolkata with several localized zones of heavy rain and this is found to be well supported by the nearby station observations.This study establishes that DWR observations along with hourly satellite imageries are able to capture the evolution of Nor ’westers.The study also shows that the composite DWR-satellite information is a reliable tool for nowcasting the location,time and path of movement of Nor ’westers.Based on these observations,a conceptual model of the Nor ’wester is proposed.

    • A study of lightning activity over land and oceanic regions of India

      Asha Nath G K Manohar K K Dani P C S Devara

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      Monthly variations of lightning activity over typical land and oceanic regions of India were examined using satellite data (OTD)for a 5-year period (1995-1999).It is noted that the nature of variation between surface air maximum temperature (𝑇_max) ,thunderstorm days (Th_n) ,and lightning flash count over ER and WR showed remarkable correspondence and sensitivity with each other on monthly time scale.As we move out of winter season and enter the monsoon season,via pre-monsoon season,the WR undergoes cooling relative to the ER in the range 0.1-1.2°C. As a result,WR experiences reduction of thunder days and lowering in flash count. This decrease in 𝑇_max Th_{n} and flash count over WR may also be associated with relatively small values of 𝑇𝜃 w and CAPE in comparison with similar values over ER during the monsoon sea-son.Our observation of associated reduction in Th_n and lightning count per 1°C cooling in surface air maximum temperature suggests reduction of ∼3.5 thunderstorms per station and 73 flashes. Comparison of lightning flashes between pairs of coastal,oceanic,arid-zone,hilly,and island stations reveals distinct relationship between climate regime and intensity of lightning activity. We may conclude the results of this study by saying that the overhead lightning activity is a clear reflection of the status of the underlying ground-earth properties. A close and continuous monitoring of lightning activity may be considered as a need of present day scientific studies.

    • On the diurnal ranges of Sea Surface Temperature (SST) in the north Indian Ocean

      S S C Shenoi N Nasnodkar G Rajesh K Jossia Joseph I Suresh A M Almeida

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      This paper describes the variability in the diurnal range of SST in the north Indian Ocean using in situ measurements and tests the suitability of simple regression models in estimating the diurnal range.SST measurements obtained from 1556 drifting and 25 moored buoys were used to determine the diurnal range of SSTs.The magnitude of diurnal range of SST was highest in spring and lowest in summer monsoon.Except in spring,nearly 75 –80%of the observations reported diurnal range below 0.5°C.The distributions of the magnitudes of diurnal warming across the three basins of north Indian Ocean (Arabian Sea,Bay of Bengal and Equatorial Indian Ocean)were similar except for the differences between the Arabian Sea and the other two basins during November-February (winter monsoon)and May.The magnitude of diurnal warming that depended on the location of temperature sensor below the water level varied with seasons.In spring,the magnitude of diurnal warming diminished drastically with the increase in the depth of temperature sensor.The diurnal range estimated using the drifting buoy data was higher than the diurnal range estimated using moored buoys fitted with temperature sensors at greater depths.

      A simple regression model based on the peak solar radiation and average wind speed was good enough to estimate the diurnal range of SST at ∼1.0 m in the north Indian Ocean during most of the seasons except under low wind-high solar radiation conditions that occur mostly during spring. The additional information on the rate of precipitation is found to be redundant for the estimation of the magnitude of diurnal warming at those depths.

    • Seasonal variation in the biochemical composition of red seaweed (Catenella repens) from Gangetic delta, northeast coast of India

      Kakoli Banerjee Rajrupa Ghosh Sumit Homechaudhuri Abhijit Mitra

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      The biochemical composition of red seaweeds,Catenella repens was investigated in this present study along with subsequent analysis of relevant physico-chemical variables.In this study, the relationship between the nutritive components of this species and the ambient environmental parameters was established.Protein content varied from 2.78 ± 0.30% of dry weight (stn.3)to 16.03 ± 0.96% of dry weight (stn.1) with highest values during monsoon.The protein levels were positively correlated with dissolved nitrate content and negatively correlated with water temperature (except stn.3)and salinity.Carbohydrate content of this species varied significantly (𝑝 > 0.05) during pre-monsoon between stations and the values showed positive relationship with salinity and surface water temperature.In contrast to carbo- hydrate,lipid concentration was lowest in values and varied very slightly between seasons and stations.Astaxanthin content of the seaweed species was greater in pre-monsoon than monsoon and post-monsoon in all the selected stations.Compared with the three seasons, samples of red seaweed collected in pre-monsoon has high carbohydrate –astaxanthin in contrast to protein –lipid which showed high values during monsoon.Statistical analysis computed among the environmental and biochemical parameters suggests the potential role played by the abiotic parameters on biosynthetic pathways of seaweed.This paper also highlights the influence of the nutritional quality of water that can be used for mass cultivation of Catenella repens.

    • Groundwater flow modelling of Yamuna–Krishni interstream, a part of central Ganga Plain Uttar Pradesh

      Izrar Ahmed Rashid Umar

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      Groundwater is a major source of water for agricultural and domestic requirements in western Uttar Pradesh.Due to increasing agricultural requirements the abstraction of groundwater has increased manifold in the last two-to-three decades.The quaternary alluvium hosts the aquifer in the region.The study area forms a part of Yamuna –Krishni inter fluve.Although the area hosts potential aquifers these have been adversely affected by poor management.For effective ground water management of a basin it is essential that a careful water balance study should be carried out. Keeping this in mind groundwater flow modelling was attempted to simulate the behaviour of the flow system and evaluate the water balance.The groundwater flow modelling was carried out.The horizontal flows,seepage losses from unlined canals,recharge from rainfall and irrigation return flows were applied using different boundary packages available in Visual MODFLOW,Pro 4.1. The river aquifer interaction was simulated using the river boundary package.Hydraulic conductivity values were applied to specific zones and these ranged from 9.8 to 26.6 m/day.Recharge due to rainfall and irrigation returns were assigned to respective zones.Pumping rates of 500 m3/day$, 1000 m3/day$, 1500 m3/day, 2000 m3/day and 2500 m3/day were applied to appropriate areas of the model to simulate areas of stress.The zone budget shows a water balance de ficit for the period June 2006 to June 2007. The total recharge to the study area is 160.21 million m3 (Mcum). The groundwater draft through pumping is of the order of 233.56 Mcum, thus leaving a deficit balance of −73.35 Mcum. The sensitivity of the model to input parameters was tested by varying the parameters of interest over a range of values, monitoring the response of the model and determining the root mean square error of the simulated groundwater heads to the measured heads. These analyses showed that the model is most sensitive to hydraulic conductivity and recharge parameters. Three scenarios were considered to predict aquifer responses under varied conditions of groundwater bstraction.

    • Estimation of snow cover distribution in Beas basin, Indian Himalaya using satellite data and ground measurements

      H S Negi A V Kulkarni B S Semwal

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      In the present paper,a methodology has been developed for the mapping of snow cover in Beas basin,Indian Himalaya using AWiFS (IRS-P6)satellite data.The complexities in the mapping of snow cover in the study area are snow under vegetation,contaminated snow and patchy snow. To overcome these problems,field measurements using spectroradiometer were carried out and reflectance/snow indices trend were studied.By evaluation and validation of different topographic correction models,it was observed that,the normalized difference snow index (NDSI)values remain constant with the variations in slope and aspect and thus NDSI can take care of topography effects.Different snow cover mapping methods using snow indices are compared to find the suitable mapping technique.The proposed methodology for snow cover mapping uses the NDSI (estimated using planetary re flectance),NIR band reflectance and forest/vegetation cover information.The satellite estimated snow or non-snow pixel information using proposed methodology was validated with the snow cover information collected at three observatory locations and it was found that the algorithm classify all the sample points correctly,once that pixel is cloud free.The snow cover distribution was estimated using one year (2004 –05)cloud free satellite data and good correlation was observed between increase/decrease areal extent of seasonal snow cover and ground observed fresh snowfall and standing snow data.

    • Analytical solutions of one-dimensional advection–diffusion equation with variable coefficients in a finite domain

      Atul Kumar Dilip Kumar Jaiswal Naveen Kumar

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      Analytical solutions are obtained for one-dimensional advection –diffusion equation with variable coefficients in a longitudinal finite initially solute free domain,for two dispersion problems.In the first one,temporally dependent solute dispersion along uniform flow in homogeneous domain is studied.In the second problem the velocity is considered spatially dependent due to the inhomogeneity of the domain and the dispersion is considered proportional to the square of the velocity. The velocity is linearly interpolated to represent small increase in it along the finite domain.This analytical solution is compared with the numerical solution in case the dispersion is proportional to the same linearly interpolated velocity.The input condition is considered continuous of uniform and of increasing nature both.The analytical solutions are obtained by using Laplace transformation technique.In that process new independent space and time variables have been introduced. The effects of the dependency of dispersion with time and the inhomogeneity of the domain on the solute transport are studied separately with the help of graphs.

    • Detection of sub-basaltic sediments by a multi-parametric joint inversion approach

      Ajay Manglik Saurabh K Verma K H Singh

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      In many parts of the world sedimentary horizons with potential for hydrocarbon are located below flood basalt provinces.However,the presence of high velocity basaltic overburden makes delineation of sediments difficult due to the low velocity layer problem.Electrical and electromagnetic methods have been used in such scenarios because of the good electrical conductivity contrast between basalts and underlying sediments.However,mapping of the target sediments becomes difficult when the layer is thin as the data errors due to inherent noise lead to equivalent solutions.To tackle such difficult situations,a joint inversion scheme incorporating seismic reflection and refraction, magnetotelluric and deep electrical resistivity datasets is presented. Efficacy of the scheme is tested for a model comprising a thin sedimentary layer sandwiched between a thick basalt cover and a granitic basement.The results indicate that the parameters of the target sedimentary layer are either poorly resolved or equivalent solutions are obtained by the inversion of individual datasets. Joint inversions of seismic reflection (RFLS)and refraction (RFRS),or DC and MT dataset pairs provide improved results and the range of equivalent solutions is narrowed down.Combination of any three of the above datasets leads to further narrowing of this range and improvements in mean model estimates.Joint inversion incorporating all the datasets is found to yield good estimates of the structure.Resolution analysis is carried out to appraise estimates of various model parameters obtained by jointly inverting different combinations of datasets.

    • Consolidation of a poroelastic half-space with anisotropic permeability and compressible constituents by axisymmetric surface loading

      Sarva Jit Singh Raman Kumar Sunita Rani

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      The fully coupled Biot quasi-static theory of linear poroelasticity is used to study the consolidation of a poroelastic half-space caused by axisymmetric surface loads.The fluid and solid constituents of the poroelastic medium are compressible and its permeability in the vertical direction is different from its permeability in the horizontal direction.An analytical solution of the governing equations is obtained by taking the displacements and the pore pressure as the basic state variables and using a combination of the Laplace and Hankel transforms.The problem of an axisymmetric normal load is discussed in detail.An explicit analytical solution is obtained for normal disc loading.Detailed numerical computations reveal that the anisotropy in permeability as well as the com-pressibilities of the fluid and solid constituents of the poroelastic medium have significant effects on the consolidation of the half-space.The anisotropy in permeability may accelerate the consolidation process and may lead to a dilution in the theoretical prediction of the Mandel –Cryer effect. The compressibility of the solid constituents may also accelerate the consolidation process.

    • Trachyhystrichosphaera: An age-marker acanthomorph from the Bhander group, upper Vindhyan, Rajasthan

      Purnima Srivastava

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      A highly diversified, advanced and exceptionally well preserved microfossil assemblage, dominated by a planktic community,has been recorded from petrographic thin sections of chert belonging to the Sirbu Shale Formation,Bhander group,upper Vindhyans,Rajasthan.Recently, it was noticed that the assemblage also contains well preserved,large-sized acanthomorphic acritarchs, Trachyhystrichosphaera considered to be an age-marker microfossil of the Cryogenian (850 –630 Ma).It is reported for the first time from any Indian microfossil assemblage of Proterozoic succession.The other microfossils of the Sirbu Shale Formation are:well preserved simple,small and large-sized sphaeromorphs;complex acanthomorphs,cyanobacterial community;especially a very small-sized but exceptionally well preserved Obruchevella ,a form resembling Volvox colonies; cf.vase-shaped microfossils and morphologies,possibly inclining towards fungal affinity,or lichen- like symbiotic associations of algae and fungi.Till date, Trachyhystrichosphaera has so far not been reported from successions older than the Tonian (1000 –850 Ma).It is believed that acanthomorphs attained maximum size in Ediacaran (630 –542 Ma),and further decreased in size in the Cambrian.The global paleontological literature indicates that Trachyhystrichosphaera ranges in age from Tonian –Ediacaran (1000 –542 Ma).

      The present record of Trachyhystrichosphaera as well as the earlier studies of micro and megascopic life of the Bhander Group in general and the Sirbu Shale in particular (aided by the absence of any Cambrian fossil record)indicate that in all possibilities,age of the Sirbu Shale should lie near Cryogenian (850 –630 Ma)and the uppermost Bhander group,may incline towards the Ediacaran (630 –542 Ma).

    • Application of Markov chain and entropy analysis to lithologic succession – an example from the early Permian Barakar Formation, Bellampalli coalfield, Andhra Pradesh, India

      Ram Chandra Tewari D P Singh Z A Khan

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      A statistical approach by a modified Markov process model and entropy function is used to prove that the early Permian Barakar Formation of the Bellampalli coal field developed distinct cyclicities during deposition.From results,the transition path of lithological states typical for the Bellampalli basin is as:coarse to medium-grained sandstone $\longrightarrow $ interbedded fine-grained sandstone/shale $\longrightarrow $ shale $\longrightarrow $ coal and again shale.The majority of cycles are symmetrical but asymmetrical cycles are present as well.The chi-square stationarity test implies that these cycles are stationary in space and time.The cycles are interpreted in terms of in-channel,point bar and overbank facies association in a fluvial system.The randomness in the occurrence of facies within a cycle is evaluated in terms of entropy,which can be calculated from the Markov matrices.Two types of entropies are calculated for every facies state;entropy after deposition 𝐸 (post)and entropy before deposition 𝐸(pre),which together form entropy set;the entropy for the whole system is also calculated.These values are plotted and compared with Hattori ’s idealized plots,which indicate that the sequence is essentially a symmetrical cycle (type-B of Hattroi).

      The symmetrical cyclical deposition of early Permian Barakar Formation is explained by the lateral migration of stream channels in response to varying discharge and rate of deposition across the alluvial plain.In addition,the fining upward cycles in the upper part enclosing thick beds of fine clastics,as well as coal may represent differential subsidence of depositional basin.

    • Eco-restoration of a high-sulphur coal mine overburden dumping site in northeast India: A case study

      J Dowarah H P Deka Boruah J Gogoi N Pathak N Saikia A K Handique

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      Eco-restoration of mine overburden (OB)or abandoned mine sites is a major environmental concern.In the present investigation,an integrated approach was used to rejuvenate a high-sulphur mine OB dumping site in the Tirap Collieries,Assam,India,which is situated in the Indo-Burma mega-biodiversity hotspot.A mine OB is devoid of true soil character with poor macro and micronutrient content and contains elevated concentrations of trace and heavy metals.Planting of herbs, shrubs,cover crops and tree species at close proximity leads to primary and secondary sere state succession within a period of 3 to 5 years.A variety of plant species were screened for potential use in restoration:herbs,including Sccharum spontaneum, Cymbopogon winterianus Jowitt (citronella), and Cymbopogon flexuosus (lemon grass)cover plants,including Mimosa strigillosa M. striata and M. pigra; shrubs,including Sesbania rostrata (dhaincha)and Cassia streata (cassia);and tree species,including Gmelina arborea (gomari)and Dalbergia sissoo (sissoo).Amendment with unmined soil and bio-organic matter was required for primary establishment of some plant species. Management of these plant species at the site will ensure long term sustainable eco-restoration of the coal mine-degraded land.

    • High-resolution satellite image segmentation using Hölder exponents

      Debasish Chakraborty Gautam Kumar Sen Sugata Hazra

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      Texture in high-resolution satellite images requires substantial amendment in the conventional segmentation algorithms. A measure is proposed to compute the Hölder exponent (HE) to assess the roughness or smoothness around each pixel of the image. The localized singularity information is incorporated in computing the HE. An optimum window size is evaluated so that HE reacts to localized singularity. A two-step iterative procedure for clustering the transformed HE image is adapted to identify the range of HE, densely occupied in the kernel and to partition Hölder exponents into a cluster that matches with the range. Hölder exponent values (noise or not associated with the other cluster) are clubbed to a nearest possible cluster using the local maximum likelihood analysis.

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