• Issue front cover thumbnail

      Volume 125, Issue 4

      June 2016,   pages  677-898

    • Impact of high resolution land surface initialization in Indian summer monsoon simulation using a regional climate model

      C K Unnikrishnan M Rajeevan S Vijaya Bhaskara Rao

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      The direct impact of high resolution land surface initialization on the forecast bias in a regional climatemodel in recent years over Indian summer monsoon region is investigated. Two sets of regional climatemodel simulations are performed, one with a coarse resolution land surface initial conditions and secondone used a high resolution land surface data for initial condition. The results show that all monsoonyears respond differently to the high resolution land surface initialization. The drought monsoon year2009 and extended break periods were more sensitive to the high resolution land surface initialization.These results suggest that the drought monsoon year predictions can be improved with high resolutionland surface initialization. Result also shows that there are differences in the response to the land surfaceinitialization within the monsoon season. Case studies of heat wave and a monsoon depression simulationshow that, the model biases were also improved with high resolution land surface initialization. Theseresults show the need for a better land surface initialization strategy in high resolution regional modelsfor monsoon forecasting.

    • Sensitivity of tropical cyclone characteristics to the radial distribution of sea surface temperature

      Deepika Rai S Pattnaik P V Rajesh

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      Sea Surface Temperature (SST) is crucial for the development and maintenance of a tropical cyclone(TC) particularly below the storm core region. However, storm data below the core region is the mostdifficult to obtain, hence it is not clear yet that how sensitive the radial distribution of the SST impactthe storm characteristic features such as its inner-core structures, translational speed, track, rainfalland intensity particularly over the Bay of Bengal. To explore the effects of radial SST distributionon the TC characteristics, a series of numerical experiments were carried out by modifying the SSTat different radial extents using two-way interactive, triply-nested, nonhydrostatic Advanced WeatherResearch and Forecast (WRF-ARW) model. It is found that not only the SST under the eyewall (coreregion) contribute significantly to modulate storm track, translational speed and intensity, but also thoseoutside the eyewall region (i.e., 2–2.5 times the radius of maximum wind (RMW)) play a vital role indefining the storm’s characteristics and structure. Out of all the simulated experiments, storm wherethe positive radial change of SST inducted within the 75 km of the storm core (i.e., P75) produced thestrongest storm. In addition, N300 (negative radial changes at 300 km) produced the weakest storm.Further, it is found that SST, stronger within 2–2.5 times of the RMW for P75 experiment, plays adominant role in maintaining 10 m wind speed (WS10), surface entropy flux (SEF) and upward verticalvelocity (w) within the eyewall with warmer air temperature (T) and equivalent potential temperature(θe) within the storm’s eye compared to other experiments.

    • Validating quantitative precipitation forecast for the Flood Meteorological Office, Patna region during 2011–2014

      R K Giri Jagabandhu Panda Sudhansu S Rath Ravindra Kumar

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      In order to issue an accurate warning for flood, a better or appropriate quantitative forecasting of precipitationis required. In view of this, the present study intends to validate the quantitative precipitationforecast (QPF) issued during southwest monsoon season for six river catchments (basin) under theflood meteorological office, Patna region. The forecast is analysed statistically by computing various skillscores of six different precipitation ranges during the years 2011–2014. The analysis of QPF validationindicates that the multi-model ensemble (MME) based forecasting is more reliable in the precipitationranges of 1–10 and 11–25 mm. However, the reliability decreases for higher ranges of rainfall and also forthe lowest range, i.e., below 1 mm. In order to testify synoptic analogue method based MME forecastingfor QPF during an extreme weather event, a case study of tropical cyclone Phailin is performed. It isrealized that in case of extreme events like cyclonic storms, the MME forecasting is qualitatively usefulfor issue of warning for the occurrence of floods, though it may not be reliable for the QPF. However,QPF may be improved using satellite and radar products.

    • Developing synergy regression models with space-borne ALOS PALSAR and Landsat TM sensors for retrieving tropical forest biomass

      Suman Sinha C Jeganathan L K L K Sharma M S Nathawat Anup K Das Shiv Mohan

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      Forest stand biomass serves as an effective indicator for monitoring REDD (reducing emissions fromdeforestation and forest degradation). Optical remote sensing data have been widely used to derive forestbiophysical parameters inspite of their poor sensitivity towards the forest properties. Microwave remotesensing provides a better alternative owing to its inherent ability to penetrate the forest vegetation.This study aims at developing optimal regression models for retrieving forest above-ground bole biomass(AGBB) utilising optical data from Landsat TM and microwave data from L-band of ALOS PALSARdata over Indian subcontinental tropical deciduous mixed forests located in Munger (Bihar, India). Spatialbiomass models were developed. The results using Landsat TM showed poor correlation (R^2 =0.295and RMSE=35 t/ha) when compared to HH polarized L-band SAR (R^2 =0.868 and RMSE=16.06 t/ha).However, the prediction model performed even better when both the optical and SAR were used simultaneously(R^2 =0.892 and RMSE=14.08 t/ha). The addition of TM metrics has positively contributed inimproving PALSAR estimates of forest biomass. Hence, the study recommends the combined use of bothoptical and SAR sensors for better assessment of stand biomass with significant contribution towardsoperational forestry.

    • Interpolation study on ambient gamma levels in parts of Khasi Hills, Meghalaya (India): Preliminary findings for U exploration

      B M Kukreti G K Sharma Pramod Kumar Sandeep Hamilton

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      This paper discusses an experimental approach to examine uranium exploration avenue over the geologicallyextended parts of Mahadek basin in Meghalaya, amid some of the environmental constraints. Studycomprises periodic measurements of prevailing ambient gamma levels across 320 georeference points, inrelation to the major litho units of Mahadek basin, covering 673 line km of Khasi Hills. Acquired sampledata points were then analysed in geostatistical software (Surfer^{TM}) to develop analytical model of samplevariogram having bearing on the uranium exploration in the area. Study findings have given encouragingsurface indicators with mostly elevated gamma levels over the parts of West Khasi Hills. Delineatedgamma anomalous zones are lithologically well correlated including to that of existing uranium occurrencesin the basin. Identified anomalous zones over the parts of West Khasi Hills by this study work, aremainly associated with the Mahadek sandstone (Upper and Lower Mahadek) and Precambrian basementgranites. Lower Mahadek sandstone is host rock for uranium mineralisation in the basin. Initial findingssuggest with the closer spatial resolution (∼1 km) of sample data points, the approach adopted by thestudy work holds promising application in locating potential uranium exploration targets especially tothe extended and inaccessible parts of the basin.

    • Comparison of ionospheric characteristic parameters obtained by GPS and ionosonde with IRI model over China

      Cheng Wang

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      This paper presents a comparison of ionospheric characteristic parameters obtained by a GPS networkand three ionosondes at Mohe (122.4^◦E, 53.5^◦N, dip angle 70.983^◦N), Zuolingzhen (114.6^◦E, 30.5^◦N, dipangle 46.350^◦N), and Fuke (109.1^◦E, 19.5^◦N, dip angle 27.083^◦N) located in China with an IRI model inthe year 2011. Observed NmF2 and hmF2 values at the three stations are compared with IRI2007 andIRI2012 predictions, respectively. The results show that there are clear linear correlations between theobserved values and the IRI model predicted values. The IRI model gives overestimations at the threestations mostly in 2011. For the NmF2 and hmF2 values, most of the results show that the IRI2012predicted values are closer to the observed values compared with those of IRI2007. Additionally, theGPS TEC values derived from the Crustal Movement Observation Network of China (CMONOC) arecompared with the IRI2012 predictions. From the results, it is evident that the IRI2012 model predictionsfollow the normal trend of diurnal variation of GPS measured TEC monthly means but do not reproducethe measured data well. The IRI2012 model overestimates electron density in the latter part of spring aswell as the first half of autumn and winter and underestimates electron density in early spring and thelatter part of autumn. Referring to GPS TEC, the precision of the IRI2012 model predicted TEC valuesis ∼5 TECU over China. It may also be noted that there are two discontinuities of IRI-TEC monthlymeans appearing in November and December of the year 2011. This brings a bias of ∼3 TECU of TECvalues between two adjacent months.

    • Modelling discontinuous well log signal to identify lithological boundaries via wavelet analysis: An example from KTB borehole data

      Amrita Singh Saumen Maiti R K Tiwar

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      Identification of sharp and discontinuous lithological boundaries from well log signal stemming fromheterogeneous subsurface structures assumes a special significance in geo-exploration studies. Well logdata acquired from various geological settings generally display nonstationary/nonlinear characteristicswith varying wavelengths and frequencies. Modelling of such complex well-log signals using the conventionalsignal processing techniques either fails to catch-up abrupt boundaries or at the best, do notprovide precise information on insidious lithological discontinuities. In this paper, we have proposed anew wavelet transform-based algorithm to model the abrupt discontinuous changes from well log databy taking care of nonstationary characteristics of the signal. Prior to applying the algorithm on thegeophysical well data, we analyzed the distribution of wavelet coefficients using synthetic signal generatedby the first order nonstationary auto-regressive model and then applied the method on actual welllog dataset obtained from the KTB bore hole, Germany. Besides identifying the formation of layeredboundaries, the underlying method also maps some additional formation boundaries, which were hithertoundetected at the KTB site. The results match well with known geological lithostratigraphy andwill be useful for constraining the future model of KTB bore hole data.

    • Influence of storm magnitude and watershed size on runoff nonlinearity

      Kwan Tun Lee Jen-Kuo Huang

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      The inherent nonlinear characteristics of the watershed runoff process related to storm magnitude andwatershed size are discussed in detail in this study. The first type of nonlinearity is referred to rainfallrunoffdynamic process and the second type is with respect to a Power-law relation between peakdischarge and upstream drainage area. The dynamic nonlinearity induced by storm magnitude was firstdemonstrated by inspecting rainfall-runoff records at three watersheds in Taiwan. Then the derivation ofthe watershed unit hydrograph (UH) using two linear hydrological models shows that the peak dischargeand time to peak discharge that characterize the shape of UH vary event-to-event. Hence, the intentionof deriving a unique and universal UH for all rainfall-runoff simulation cases is questionable. In contrast,the UHs by the other two adopted nonlinear hydrological models were responsive to rainfall intensitywithout relying on linear proportion principle, and are excellent in presenting dynamic nonlinearity.Based on the two-segment regression, the scaling nonlinearity between peak discharge and drainagearea was investigated by analyzing the variation of Power-law exponent. The results demonstrate thatthe scaling nonlinearity is particularly significant for a watershed having larger area and subjecting toa small-size of storm. For three study watersheds, a large tributary that contributes relatively greatdrainage area or inflow is found to cause a transition break in scaling relationship and convert the scalingrelationship from linearity to nonlinearity.

    • How to update design floods after the construction of small reservoirs and check dams: A case study from the Daqinghe river basin, China

      Jianzhu Li Huafeng Sun Ping Feng

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      Several small reservoirs and a large number of check dams had been constructed in theWangkuai reservoirwatershed after 1970s, and flood time series lacked stationarity, which affected the original design floodhydrographs for the Wangkuai reservoir. Since the location, storage capacity and drainage area of thelarge number of check dams were unknown, we present a method to estimate their total storage capacities(TSC) and total drainage areas (TDA) by using the recorded rainstorm and flood data. On the basisof TSC and TDA, the flood events which occurred in an undisturbed period were reconstructed undercurrent conditions to obtain a stationary flood series. A frequency analysis was subsequently performedto assess the design flood peak and volume for both small and medium design floods with a 10–200year return period. For large and catastrophic floods, it was assumed that the upstream check dams andsmall reservoirs would be destroyed, and water stored in these hydraulic structures were re-routed to theWangkuai reservoir by unit hydrograph. The modified flood peak and volume decreased for floods witha 10–200 year return period when compared to the current design flood. But for large design floods witha return period exceeding 500 years, peak discharge increased. This study provides a new method fordesign flood calculation or modification of the original design flood in watersheds with a large numberof check dams.

    • Hydrological indications of aeolian salts in mid-latitude deserts of northwestern China

      Bing-Qi Zhu

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      Large sandy deserts in middle latitude of northwestern China were studied on salt variations in modernand ancient aeolian sediments, aiming to explore their hydrological indications at the present and past.Globally, sulphate is rich in arid to semi-arid deserts, including the aeolian loess sediments in China andsoils in low-latitude deserts, but is less common in the aeolian sediments from the mid-latitude desertsin this study. The compositional differences between aeolian salts and local natural waters is evident,indicating the chemistry of aeolian salts and the associated parent brines may be significantly differentthan that predicted for hydrologically closed systems. The formation of aeolian salts in the studieddeserts is strongly controlled by earth surface processes in a large scale but not in a local scale. Verticalchanges in facies and salinities are abrupt in the studied palaeo-aeolian sediment samples, which wereinterbedded by lacustrine/fluvial sediments with OSL and ^{14}C ages ranging between 40 and 2 ka BP,reflecting rapid high-amplitude changes in hydrological settings during late Pleistocene to later Holocenein these ancient playa systems. A great difference in salt composition between aeolian and lacustrinesediments suggests that the inorganic salt is a latent geoproxy in revealing local hydrological variationsand climate change in the desert areas. But the environmental indications could be amphibolous for thesedimentary sequences with dual/multiple depositional end-members; under this situation an increase insequence salinity does not always represent an enhanced environmental aridity. Ancient playas are aridor humid at the same time based on several sporadic records is not a valid approach to correlation of saltdeposits in adjacent saline playa basin in the studied areas. Effects of earth surface processes includingerosion, deposition and other processes on sediment properties will bias the hydrological implications ofsediment salinity.

    • Geomorphic observations from southwestern terminus of Palghat Gap, south India and their tectonic implications

      Yogendra Singh Biju John G P Ganapathy Abhilash Abhilash George S Harisanth K S Divyalakshmi Sreekumari Kesavan

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      The region around Wadakkancheri, Trichur District, Kerala is known for microseismic activity, since1989. Studies, subsequent to 2nd December 1994 (M=4.3) earthquake, identified a south dippingactive fault (Desamangalam Fault) that may have influenced the course of Bharathapuzha River. Theongoing seismicity is concentrated on southeast of Wadakkancheri and the present study concentratedfurther south of Desamangalam Fault. The present study identifies the northwestern continuity of NW–SE trending Periyar lineament, which appears to have been segmented in the area. To identify the subtlelandform modifications induced by ongoing tectonic adjustments, we focused on morphometric analysis.The NW–SE trending lineaments appear to be controlling the sinuosity of smaller rivers in the area,and most of the elongated drainage basins follow the same trend. The anomalies shown in conventionalmorphometric parameters, used for defining basins, are also closely associated with the NW–SE trendingPeriyar lineament/s. A number of brittle faults that appear to have been moved are consistent withthe present stress regime and these are identified along the NW–SE trending lineaments. The currentseismic activities also coincide with the zone of these lineaments as well as at the southeastern endof Periyar lineament. These observations suggest that the NW–SE trending Periyar lineaments/faultsmay be responding to the present N–S trending compressional stress regime and reflected as the subtlereadjustments of the drainage configuration in the area.

    • Interpreting the geomorphometric indices for neotectonic implications: An example of Alaknanda valley, Garhwal Himalaya, India

      Naresh Rana Sunil Singh Y P Sundriyal G S Rawat Navin Juyal

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      Tectonic process can influence the erosion and exert the first order impression on hydrographic networkof an area. Geomorphometry, a mathematical analysis of the configuration of the landforms, allows quantifyingthe degree of landform evolution and is widely used as a measure of tectonic deformation/uplift.Alaknanda valley lies in the tectonically active Garhwal Himalaya which has experienced two disastrouslarge earthquakes in the last two decades. Morphometric analyses of the valley were carried out in a fluvialerosion dominated regime and the morphometric indices were derived from the ASTER (30 m × 30 mpixel) Digital Elevation Model (DEM) using Arc GIS. The results of the analyses reveal two zones ofhigh deformation/uplift in the valley, viz., the zone of high deformation proximal to the Main CentralThrust (MCT) in the Inner Lesser Himalaya (ILH) and the second zone of moderate deformation/upliftin the Outer Lesser Himalaya (OLH), south of the Tons Thrust (TT). The high deformation in the ILHis ascribed to the focussed convergence and high precipitation; however, the causes for the moderatedeformation in the OLH are yet to be established.

    • Identification of seismically susceptible areas in western Himalaya using pattern recognition

      Mridula Amita Sinvhal Hans Raj Wason

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      Seismicity in the western Himalayas is highly variable. Several historical and instrumentally recordeddevastating earthquakes originated in the western Himalayas which are part of the Alpine–Himalayanbelt. Earthquakes cause tremendous loss of life and to the built environment. The amount of loss interms of life and infrastructure has been rising continuously due to significant increase in population andinfrastructure. This study is an attempt to identify seismically susceptible areas in western Himalaya,using pattern recognition technique. An area between latitude 29◦–36◦N and longitude 73◦–80◦E wasconsidered for this study. Pattern recognition starts with identification, selection and extraction of featuresfrom seismotectonic data. These features are then subjected to discriminant analysis and the studyarea was classified into three categories, viz., Area A: most susceptible area, Area B: moderately susceptiblearea, and Area C: least susceptible area. Results show that almost the entire states of HimachalPradesh and Uttarakhand and a portion of Jammu & Kashmir are classified as Area A, while most ofJammu & Kashmir is classified as Area B and the Indo-Gangetic plains are classified as Area C.

    • Back-thrusting in Lesser Himalaya: Evidences from magnetic fabric studies in parts of Almora crystalline zone, Kumaun Lesser Himalaya

      Amar Agarwal K K K K Agarwal R Bali Chandra Prakash Gaurav Joshi

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      The present study aims to understand evolution of the Lesser Himalaya, which consists of (meta) sedimentaryand crystalline rocks. Field studies, microscopic and rock magnetic investigations have beencarried out on the rocks near the South Almora Thrust (SAT) and the North Almora Thrust (NAT),which separates the Almora Crystalline Zone (ACZ) from the Lesser Himalayan sequences (LHS). Theresults show that along the South Almora Thrust, the deformation is persistent; however, near theNAT deformation pattern is complex and implies overprinting of original shear sense by a youngerdeformational event. We attribute this overprinting to late stage back-thrusting along NAT, active afterthe emplacement of ACZ. During this late stage back-thrusting, rocks of the ACZ and LHS were coupled.Back-thrusts originated below the Lesser Himalayan rocks, probably from the Main Boundary Thrust,and propagated across the sedimentary and crystalline rocks. This study provides new results frommultiple investigations, and enhances our understanding of the evolution of the ACZ.

    • Effect of irregularity on torsional surface waves in an initially stressed anisotropic porous layer sandwiched between homogeneous and non-homogeneous half-space

      Anup Saha Santimoy Kundu Shishir Gupta Pramod Kumar Vaishnav

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      The present paper is concerned with the propagation of torsional surface waves in an initially stressedanisotropic porous layer sandwiched between homogeneous and non-homogeneous half-space. We assumethe quadratic inhomogeneity in rigidity and density in the lower half-space and irregularity is taken inthe form of rectangle at the interface separating the layer from the lower half-space. The dispersionequation for torsional waves has been obtained in a closed form. Velocity equation is also obtained inthe absence of irregularity. The study reveals that the presence of irregularity, initial stress, porosity,inhomogeneity and anisotropy factor in the dispersion equation approves the significant effect of theseparameters in the propagation of torsional waves in porous medium. It has also been observed that fora uniform media, the velocity equation reduces to the classical result of Love wave.

    • Erratum to: Mapping sediment thickness of Islamabad city using empirical relationships: Implications for seismic hazard assessment

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