ENSO, IOD and Indian Summer Monsoon in NCEP climate forecast system     

Samir Pokhrel  H. S. Chaudhari  Subodh K. Saha  Ashish Dhakate  R. K. Yadav  Kiran Salunke  S. Mahapatra  Suryachandra A. Rao 《Climate Dynamics》2012,39(9-10):2143-2165

El Ni?o-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Indian Summer Monsoon rainfall features are explored statistically and dynamically using National Centers for Environment Prediction (NCEP) Climate Forecast System (CFSv1) freerun in relation to observations. The 100?years of freerun provides a sufficiently long homogeneous data set to find out the mean state, periodicity, coherence among these climatic events and also the influence of ENSO and IOD on the Indian monsoon. Differences in the occurrence of seasonal precipitation between the observations and CFS freerun are examined as a coupled ocean–atmosphere system. CFS simulated ENSO and IOD patterns and their associated tropical Walker and regional Hadley circulation in pure ENSO (PEN), pure IOD (PIO) and coexisting ENSO-IOD (PEI) events have some similarity to the observations. PEN composites are much closer to the observation as compared to PIO and PEI composites, which suggest a better ENSO prediction and its associated teleconnections as compared to IOD and combined phenomenon. Similar to the observation, the model simulation also show that the decrease in the Indian summer monsoon rainfall during ENSO phases is associated with a descending motion of anomalous Walker circulation and the increase in the Indian summer monsoon rainfall during IOD phase is associated with the ascending branch of anomalous regional Hadley circulation. During co-existing ENSO and IOD years, however, the fate of Indian summer monsoon is dictated by the combined influence of both of them. The shift in the anomalous descending and ascending branches of the Walker and Hadley circulation may be somewhat attributed to the cold (warm) bias over eastern (western) equatorial Indian Ocean basin, respectively in the model. This study will be useful for identifying some of the limitations of the CFS model and consequently it will be helpful in improving the model to unravel the realistic coupled ocean–atmosphere interactions for the better prediction of Indian Summer Monsoon.  相似文献   

Chemical weathering rates in the Alaknanda–Bhagirathi river basins in Himalayas,India     

G.J. Chakrapani  R.K. Saini  S.K. Yadav 《Journal of Asian Earth Sciences》2009,34(3):347-362

The Alaknanda and Bhagirathi rivers flow through the Higher and Lesser Himalayas and confluence at Devprayag, which represents the origin of the Ganga (or Ganges) river. In the present study, a vast number of temporal and spatial samples of the river waters were collected and analyzed for major cations and anions. In addition, more recent and time series water flow data have been obtained and based on these inputs, a more refined dissolved flux rates have been estimated. The Alaknanda and Bhagirathi rivers show significant variations in chemical compositions during different seasons. Carbonate rock weathering is responsible for more than 70% of the chemical compositions in the river waters. The chemical weathering rates show seasonal variations and are much higher during non-monsoon season. The dissolved flux of Alaknanda river is much higher (1.80 × 10⁶ tons yr^?1) as compared to the Bhagirathi river (0.34 × 10⁶ tons yr^?1). The chemical weathering rates in the basin vary between 85 and 155 tons km^?2 yr^?1, which is significantly higher compared to the global average of ～24 tons km^?2 yr^?1.  相似文献   

Two‐dimensional solute transport for periodic flow in isotropic porous media: an analytical solution     

R. R. Yadav  Dilip Kumar Jaiswal  Gulrana 《水文研究》2012,26(22):3425-3433

In this article, a mathematical model is presented for the dispersion problem in finite porous media in which the flow is two‐dimensional, the seepage flow velocity is periodic, and dispersion parameter is proportional to the flow velocity. In addition to these, first‐order decay and zero‐order production parameters have also been considered directly proportional to the velocity. Retardation factor is taken into account in the present problem. First‐type boundary condition of periodic nature is considered at the extreme end of the boundary. Mixed‐type boundary condition is assumed at the origin of the domain. A classical mathematical substitution transforms the original advection–dispersion equation into diffusion equation in terms of other dependent and independent variables, with constant coefficients. Laplace transform technique is used to obtain the analytical solution. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Nighttime E region plasma irregularities over an equatorial station Trivandrum     

H.S.S. Sinha  R. Pandey  Shweta Sharma  R.N. Misra 《Journal of Atmospheric and Solar》2011,73(17-18):2444-2452

In situ measurements of electron density were made over Trivandrum (8.5°N, 76.9°E) during nighttime to study E-region plasma density irregularities. Irregularities, with vertical scale sizes from a few km to 15 cm, were detected during rocket ascent and descent. Electron density profiles during ascent and descent of an earlier nighttime rocket flight from Trivandrum are also presented. Some of the important results are as follows: (i) horizontal gradients in electron density exist in 110–120 km region with horizontal scale size of at least 40 km, (ii) based on the presence/absence of electron density structures during ascent and descent of both flights, the horizontal distance over which the gradient drift instability operates is found to be at least 80 km and 90 km, for both the flights, (iii) observed irregularities in regions of negative density gradient are suggested to be produced through the gradient drift instability (GDI) driven by vertical polarization electric field as well as by electric field produced through wind shears and those in positive gradient regions by wind driven GDI, (iv) largest irregularity amplitude (≈30%) was associated with steepest gradients and so was the presence of smallest vertical scale sizes (12 m to 15 cm), which were absent at other altitudes, (v) the spectral index of irregularities was in the range of ?2.2±0.2 for large scales (few kilometers>λ>50 m), ?3.25±0.25 for medium scales (50 m>λ>10 m) and ?2.6±0.1 for smaller scales (10 m>λ>1 m) and (vi) irregularities in large and medium scales are expected to be produced directly through GDI and the small and sum-meter scales through non-linear GDI.  相似文献   

Productivity Analysis of Draglines Operating in Horizontal and Vertical Tandem Mode of Operation in a Coal Mine—A Case Study     

Piyush Rai  Umakant Yadav  Ashok Kumar 《Geotechnical and Geological Engineering》2011,29(4):493-504

The tandem operation of draglines is in use in some of the major Indian opencast coalmines owing to the favourable geo-mining conditions, technical suitability, efficiency and economic viability. In view of the importance of tandem operation, the present study has been undertaken in a large Indian opencast coalmine in order to critically investigate the horizontal and vertical tandem operation of draglines on moderately strong and high sandstone benches (35–42 m), overlying a 15–18 m thick coal seam. The study has revealed that although the preparation of balancing diagram for planning of dragline operations is the first and the most important step, its actual implementation is equally important. Marked discrepancies in the productivity parameters as envisaged by the balancing diagram and as observed in the field studies, have been investigated and reported. The study also propounds the importance of appraisal of dragline productivity parameters, such as, cycle time, swing angle, seating position, availability, utilization, etc., in the field scale. Irrespective of the mode of operation (horizontal or vertical tandem), the study moots the concept of computation of the weighted cycle time and overall cycle time vis-à-vis swing angle variation for the draglines operating in field. The results drawn from the case study have been discussed in terms of cycle time computations, annual output computation and evaluation of earthmoving efficiency for the horizontal and vertical tandem modes of operation.  相似文献   

Probabilities for the occurrences of medium to large earthquakes in northeast India and adjoining region     

R. B. S. Yadav  J. N. Tripathi  D. Shanker  B. K. Rastogi  M. C. Das  Vikas Kumar 《Natural Hazards》2011,56(1):145-167

The return periods and occurrence probabilities related to medium and large earthquakes (M _w 4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007. The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude M _w 6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal heterogeneity and seismotectonics complexity in northeast India and adjoining regions.  相似文献   

Characterization of PM2.5 by X-ray diffraction and scanning electron microscopy–energy dispersive spectrometer: its relation with different pollution sources     

P. G. Satsangi  S. Yadav 《International Journal of Environmental Science and Technology》2014,11(1):217-232

Atmospheric PM_2.5 samples were collected by using Mini-Vol TAS air sampler. Samples were characterized directly on the collecting substrate using X-ray diffraction and scanning electron microscopy–energy dispersive spectrometer. From the analysis, it was found that Si dominate over other elements which follows the trend as Si > S > Zn > Cu > Na > Al > K > Ca > P > Fe > Mg > Ti. Based on the measurements of a population of 840 particles, particle morphology was determined by quantitative image analyzer and value of roundness (R) varies from 0.23 to 1.0 (mean 0.75) which suggests that particles vary in shape from nearly irregular to perfectly spherical shape. The mineral particulate matter identified in the atmosphere of Pune was made up of: silicates (52 %), oxides (22 %), sulfates (8 %), phosphates (7 %), carbonates (3 %) and others. A factorial analysis was carried out to determine the main elements related to the emission sources such as soil and building material erosion (~44.6 %); oil combustion (20.6 %) and fuel and biomass burning (18.3 %). Besides these factors, soot particles are abundantly present in all studied samples. Mineral particles such as sulfates aggregated to soot could have produced localized climatic effect in Pune. The emphasis of the present study is to give insight and detailed analysis of morphological and chemical composition of atmospheric particles at discrete level.  相似文献   

Distribution and risk assessment of polychlorinated biphenyls (PCBs) in the remote air and soil of Manipur,India   总被引：2，自引：0，他引：2  

Ningombam Linthoingambi Devi  Ishwar Chandra Yadav  Qi Shihua  Paromita Chakraborty  Yang Dan 《Environmental Earth Sciences》2014,72(10):3955-3967

∑₂₅PCB congeners including dioxin-like compounds were analyzed at three sites of Manipur India to assess the level of polychlorinated biphenyls (PCBs) in air and soil. The ∑₂₅PCBs were higher in urban air (average 2,454 pg/m³), followed by the mountain air (average 2,109 pg/m³) and rural air (average 1,756 pg/m³). PCB levels observed in urban air were higher compared to PCB levels reported in major Indian metropolitan cities especially along the coastal region and were comparable with the pristine sites of India and also with some pockets of China and Europe. The heavier congeners (tetra, penta, tri and hexa) were dominant in both air and soil samples and show significant correlation with the ambient temperature. Emission of PCB congeners was investigated from soil surface. The total organic carbon present in soil shows the significant correlation (r ² = 0.8; p < 0.05) with the PCBs could indicate that the PCBs originated from the similar sources. Principal component analysis revealed that the sources of higher chlorinated PCB congeners are local emissions while long-range atmospheric transport process is responsible behind elevated levels of lower chlorinated PCBs. Total calculated toxic equivalent (TEQ) levels in soil (37.17–160.5 pg/g) were superior to reported TEQ level of agricultural soil in Delhi, India (0.01–105.40 pg/g). Back trajectory analysis showed that the observed high levels of PCB at Manipur may due to movement of air masses, mostly from the Northern and Southern India and to some extent from Myanmar.  相似文献   

Resonance in a geo-centric synchronous satellite under the gravitational forces of the Sun,the Moon and the Earth including it’s equatorial ellipticity     

Rajiv Aggarwal  Sushil Yadav 《Astrophysics and Space Science》2014,349(2):727-743

Resonances in a geo-centric synchronous satellite under the gravitational forces of the Sun, the Moon and the Earth including it’s equatorial ellipticity have been investigated. The resonance at two points resulting from the commensurability between the mean motion of the satellite and Γ (angle measured from the minor axis of the Earth’s equatorial ellipse to the projection of the satellite on the plane of the equator) is analyzed. The amplitude and the time period of the oscillation have been determined by using the procedure of Brown and Shook. We have observed that the amplitude and the time period of the oscillation decrease as Γ increases in the first quadrant. The radial deviation (Δr) and the tangential deviation (r _c Δθ) have been determined. Here r _c represents the synchronous altitude. The effects of the arithmetic sum of amplitudes λ _i involved in the perturbation equations on orbital inclination 0^°≤α ₀≤90^° are shown. It is observed that $\sum_{i = 1}^{46} \lambda_{i}$ increases as α ₀ increases. We have also determined the displacement ΔD (called drift) due to the oscillatory terms under the summation sign involved in the equations of motion of the satellite. We have observed that the value of ΔD is less than 0.5^°.  相似文献   

Seasonal variation in the deformation rate in NW Himalayan region     

D. D. Khandelwal  Vineet Gahalaut  Naresh Kumar  Bhaskar Kundu  Rajeev Kumar Yadav 《Natural Hazards》2014,74(3):1853-1861

We report GPS measurements of continuous observations from the multi-parametric geophysical observatory (MPGO) at Ghuttu, Garhwal Lesser Himalaya. Other than the evidence of secular motion depicting strain accumulation due to locking of the underneath seismically active detachment, measurements at Ghuttu show annual variation of ±4 mm on horizontal component. Such variations are more prominent in the north coordinate and do not directly correlate with the meteorological parameters such as variations in rainfall, water table, and atmospheric pressure measured at the MPGO observatory. These variations are also not the artefact of data processing and network. They correlate with the water load storage in the Ganga plains, with minimum in displacement coinciding with the maximum storage of water in Ganga plains immediately after the monsoon and vice versa. Such variations also appear to cause annual variation in the low-magnitude earthquake frequency in the Himalayan region, being relatively more in the winter period.  相似文献