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排序方式: 共有388条查询结果,搜索用时 15 毫秒
11.
P V Rajesh S Pattnaik D Rai K K Osuri U C Mohanty S Tripathy 《Journal of Earth System Science》2016,125(3):475-498
In 2013, Indian summer monsoon witnessed a very heavy rainfall event (>30 cm/day) over Uttarakhand in north India, claiming more than 5000 lives and property damage worth approximately 40 billion USD. This event was associated with the interaction of two synoptic systems, i.e., intensified subtropical westerly trough over north India and north-westward moving monsoon depression formed over the Bay of Bengal. The event had occurred over highly variable terrain and land surface characteristics. Although global models predicted the large scale event, they failed to predict realistic location, timing, amount, intensity and distribution of rainfall over the region. The goal of this study is to assess the impact of land state conditions in simulating this severe event using a high resolution mesoscale model. The land conditions such as multi-layer soil moisture and soil temperature fields were generated from High Resolution Land Data Assimilation (HRLDAS) modelling system. Two experiments were conducted namely, (1) CNTL (Control, without land data assimilation) and (2) LDAS, with land data assimilation (i.e., with HRLDAS-based soil moisture and temperature fields) using Weather Research and Forecasting (WRF) modelling system. Initial soil moisture correlation and root mean square error for LDAS is 0.73 and 0.05, whereas for CNTL it is 0.63 and 0.053 respectively, with a stronger heat low in LDAS. The differences in wind and moisture transport in LDAS favoured increased moisture transport from Arabian Sea through a convectively unstable region embedded within two low pressure centers over Arabian Sea and Bay of Bengal. The improvement in rainfall is significantly correlated to the persistent generation of potential vorticity (PV) in LDAS. Further, PV tendency analysis confirmed that the increased generation of PV is due to the enhanced horizontal PV advection component rather than the diabatic heating terms due to modified flow fields. These results suggest that, two different synoptic systems merged by the strong interaction of moving PV columns resulted in the strengthening and further amplification of the system over the region in LDAS. This study highlights the importance of better representation of the land surface fields for improved prediction of localized anomalous weather event over India. 相似文献
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13.
Busyairah Syd Ali Wolfgang Schuster Washington Ochieng Arnab Majumdar 《GPS Solutions》2016,20(3):429-438
Traditionally, the surveillance component of the air traffic management system has been based on radar, which consists of two separate systems: primary radar and secondary radar, which both enable the measurement of the aircraft range and bearing to the radar station. Primary radar is based on signals emitted by a ground station simply being reflected off an object and detected by a ground-based receiver. Secondary radar also emits signals, but relies upon a transponder onboard the aircraft to emit a signal itself, modulated among others by a four-digit aircraft identity (Mode A), aircraft altitude (Mode C) and/or 24-bit unique address (Mode S). Typical accuracies of secondary radar are of the order of 0.03 NM in range and 0.07° in azimuth. However, no position integrity report is provided. Air traffic density is expected to significantly increase in the future. In order to maintain or enhance air travel efficiency, while maintaining safety, more accurate surveillance systems, with the required integrity, will be required. Automatic dependent surveillance–broadcast (ADS-B) is a new aviation surveillance system, envisioned to overcome the limitations of radar and to enhance surveillance performance and thereby increase airspace capacity. However, its high dependence on external systems such as onboard navigation and communication systems also increases the number of potential points of failure. It is important to understand and mitigate these failure modes before the system can reliably be implemented. The present study emerged as an exploratory research as part of a safety assessment framework development for the ADS-B system. It reviews the ADS-B failure modes, data collection and analysis of ADS-B and its corresponding onboard GPS data. The study identifies a set of failures common to certain aircraft models, with consistent error patterns. A key failure mode was found to be associated with the navigation data from the onboard GPS. We discuss the identified failure modes and investigate the nature and causes of these failures. The findings highlight some of the deficiencies of the current ADS-B system, which will need to be addressed before the ADS-B system can reliably be implemented. 相似文献
14.
Mousa Mohammadi Piyush Rai Umesh Singh S. K. Singh 《Geotechnical and Geological Engineering》2016,34(6):1765-1774
Dragline is highly capital intensive equipment to procure, operate and maintain in any surface mining operation. Given this, every second of operation of this capital intensive equipment is absolutely important. Improvement of even a single second in the total cycle time has a tremendous bearing on the overall performance of this equipment. In this light, the present paper is an endeavour to critically analyze the cycle time of dragline operations in a major surface coal mine in India. Rigorous statistical analysis has been performed on individual cycle time segments, of complete dragline cycle. The segmental cycle times have been found to be statistically significant and appear to be best represented by lognormal, normal and beta distributions. Furthermore, the mean time of the statistical distribution for segmental cycle time of dragline has revealed the dependence of cycle time on cut geometry and depth. Results have been illustrated in the form of figures, graphs and tables. 相似文献
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16.
The Himalayas are one of the largest cryospheric systems outside the Polar Regions, and include more than 12,000 glaciers spread over an area of about 33,000 km2. The Himalayan glaciers and snow packs retreating at an accelerating rate, thereby creating an alarming situation for the huge population that resides in northwestern India and southeastern Pakistan, as they depend on surface water resources in the region and rivers emanating from the Himalayas. This work attempts to quantify the contribution of different sources such as glacial/ice/snow melt and groundwater discharge to the Satluj River using the stable isotopes based hydrograph separation method at Ropar (foot hill) and Yusufpur in plain of Punjab, India. A mass balance model of three-component mixing has been engaged using the values of δ18O and electrical conductivity of the river water, and its discharge fraction, to estimate the time-varying relative proportion of each component from July 2013 to January 2014. The proportion of glacier melt was found to peak up to ~?64% at Ropar and ~?15% at Yusufpur during the wet summer months. The fraction of groundwater discharge was found to vary between 10–20% at Ropar and 25–35% at Yusufpur (Punjab plain) over time. The observed trend of d-excess (deuterium excess) values of river water also suggests that the glaciers and snow packs at higher altitudes contain a significant fraction of snow derived from vapor originating in the Mediterranean region, driven by the mid-latitude westerlies known as western disturbances. 相似文献
17.
Nitin D. Rai Tor A. Benjaminsen Siddhartha Krishnan C. Madegowda 《Singapore journal of tropical geography》2019,40(1):124-139
Protected areas have had significant impacts on local communities primarily through the physical removal of people. In some instances, people continue to live within protected areas due to the inability of the state to evict them. The restrictions on livelihoods placed on people living inside protected areas lead to in situ displacement. We show how conservation enclosures in the Biligiri Rangaswamy Temple Tiger Reserve have produced a class of people that the state ‘lets die’ by banning customary practices such as fire use, hunting and harvesting of forest produce. Using longitudinal ethnographic, socio‐economic and ecological data, we demonstrate that conservation policy has alienated indigenous forest dwellers from their agricultural and forest‐land. The outcomes of conservation policy include dispossession through increased crop losses, reduced income from agriculture and forest produce, as well as a forest that is dominated by weeds due to fire suppression. The ban on hunting in particular has increased wildlife densities, which has enabled the state to accumulate revenues through the establishment of wildlife tourism facilities. All in all, centralized protected area governance has changed the relationships among people, forest and the state in a way that has produced adverse effects for both livelihoods and the ecosystem. 相似文献
18.
The change in atmospheric relative humidity affects the physical and optical properties of aerosol particles. It would be
interesting to study the effect of an increase in relative humidity on the angular scattering of light by aerosols (by incorporating
the changes due to it as the complex refractive index and the parameters of the size distribution function). In the present
paper we have computed the angular scattering function for rural and urban aerosols, for light of wavelength 0.55 μn. The
results obtained for these two models, representative of different environments, are interesting and show some discriminating
features. 相似文献
19.
S. S. Iyer A. Choudhuri M. B. A. Vasconcellos U. G. Cordani 《Contributions to Mineralogy and Petrology》1984,85(1):95-101
The radioactive element distribution in the Archean granulite facies rocks of Jequié, Brazil, has been determined. The K/Rb ratios show a large spread with majority of the values falling within the normal field (K/Rb<300). The Th/U ratios fall into two groups, one group with values in the range of 1.7 to 2.6, whereas the other group show Th/U values greater than 7 (7 to 25). These distributions can be explained on the basis of the presence of accessory minerals apatite and zircon. The relatively high concentrations of the radioactive and other elements in Jequié granulites probably represents the relict primary geochemical character, little modified during metamorphism. The radiogenic heat production data for the area are calculated and using the measured regional heat flow value from nearby area an estimate of the relative thickness of the continental lithosphere is made using the model developed by Oxburgh (1981). 相似文献
20.
A neutron activation method is used to measure6Li via the reaction6Li(n, α)3H in iron meteorites. It is found that most6Li occurs in non-metallic inclusions which can be separated by dissolution of the metal in 4 M H2SO4. The non-magnetic portion of such a residue has as high as 0.9 ppm6Li, while in the bulk sample6Li ranges from 0.02 to 10 ppb. Average6Li contents (ppb) for various classes are IA, 1.8; IIAB, 1.6; and IIIA, 0.4. Cosmic-ray-produced6Li is generally much smaller than the native6Li. 相似文献