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排序方式: 共有114条查询结果,搜索用时 718 毫秒
41.
The regional climate model (RegCM4) is customized for 10-year climate simulation over Indian region through sensitivity studies on cumulus convection and land surface parameterization schemes. The model is configured over 30° E–120° E and 15° S–45° N at 30-km horizontal resolution with 23 vertical levels. Six 10-year (1991–2000) simulations are conducted with the combinations of two land surface schemes (BATS, CLM3.5) and three cumulus convection schemes (Kuo, Grell, MIT). The simulated annual and seasonal climatology of surface temperature and precipitation are compared with CRU observations. The interannual variability of these two parameters is also analyzed. The results indicate that the model simulated climatology is sensitive to the convection as well as land surface parameterization. The analysis of surface temperature (precipitation) climatology indicates that the model with CLM produces warmer (dryer) climatology, particularly over India. The warmer (dryer) climatology is due to the higher sensible heat flux (lower evapotranspiration) in CLM. The model with MIT convection scheme simulated wetter and warmer climatology (higher precipitation and temperature) with smaller Bowen ratio over southern India compared to that with the Grell and Kuo schemes. This indicates that a land surface scheme produces warmer but drier climatology with sensible heating contributing to warming where as a convection scheme warmer but wetter climatology with latent heat contributing to warming. The climatology of surface temperature over India is better simulated by the model with BATS land surface model in combination with MIT convection scheme while the precipitation climatology is better simulated with BATS land surface model in combination with Grell convection scheme. Overall, the modeling system with the combination of Grell convection and BATS land surface scheme provides better climate simulation over the Indian region. 相似文献
42.
R K Nayak N Mishra V K Dadhwal N R Patel M Salim K H Rao C B S Dutt 《Journal of Earth System Science》2016,125(6):1189-1204
This study examines the consistency between the AVHRR and MODIS normalized difference vegetation index (NDVI) datasets in estimating net primary productivity (NPP) and net ecosystem productivity (NEP) over India during 2001–2006 in a terrestrial ecosystem model. Harmonic analysis is employed to estimate seasonal components of the time series. The stationary components (representing long-term mean) of the respective NDVI time series are highly coherent and exhibit inherent natural vegetation characteristics with high values over the forest, moderate over the cropland, and small over the grassland. Both data exhibit strong semi-annual oscillations over the cropland dominated Indo-Gangetic plains while annual oscillations are strong over most parts of the country. MODIS has larger annual amplitude than that of the AVHRR. The similar variability exists on the estimates of NPP and NEP across India. In an annual scale, MODIS-based NPP budget is 1.78 PgC, which is 27% higher than the AVHRR- based estimate. It revealed that the Indian terrestrial ecosystem remained the sink of atmospheric CO 2 during the study period with 42 TgC y ?1 NEP budget associated with MODIS-based estimate against 18 TgC y ?1 for the AVHRR-based estimate. 相似文献
43.
Shailesh Nayak 《Journal of the Geological Society of India》2016,87(5):535-538
Lichenometry is an extremely useful technique in dating moraine ridge and recent glacier retreat in polar and alpine regions. The study relates the size of the lichen thallus to the minimum age of the exposure of the surface on which it grows which consequently helps in assessment of the age of the boulders. The Lichenometric studies are carried out in Kupup and Thangu area of eastern Himalaya in Sikkim and Thajiwas glacier in Ganderbal district of north western Himalaya of Jammu and Kashmir with the help of diameters of a common crustose lichen Rhizocarpon geographicum growing luxuriantly on exposed boulder. The Thajiwas glacier showed retreat of 200 m in 279 years while in Thangu and Kupup area of eastern Himalaya the retreat was estimated as 200 m in 100 and 91 years respectively. The rate of retreat was slightly more faster in eastern Himalayan (20 mm/century) than the north-western Himalaya region (18.5mm/century). 相似文献
44.
Ajay Kumar A. S. Venkatesh P. V. Ramesh Babu S. Nayak 《Journal of the Geological Society of India》2012,79(3):279-286
Petrographic and EPMA studies reveal the presence of discrete grains of uraninite and pyrite are being reported for the first
time in quartz-pebble conglomerates from western margin of Bonai granite pluton, Sundargarh district, Orissa. Uraninite grains
(2–3 μ in size) are subrounded to muffin shaped which show variation in UO2 (63.86 to 71.73 wt %), ThO2 (5.48 to 6.42 wt %) and RE2O3 (1.57 to 2.23 wt %). Pegmatitic source of uraninite is revealed by comparing UO2, ThO2, PbO, CaO content and ratios of UO2/ThO2 and CaO/ThO2 in uraninites from pegmatite and other environments and areas. Subrounded to muffin shape of uraninite, their association
with subrounded pyrite and heavies like zircon, tourmaline, chromite, monazite, magnetite and their comparable chemistry with
well established quartzpebble conglomerates of India and world are indicative of their detrital origin. Pyrite, minor chalcopyrite
and rare galena are observed as sulphide phases in conglomerate. Variable shapes of pyrite, their low Co (up to 0.16 wt %)
and Ni contents (up to 0.09 wt %) and Co/Ni ratio less than 1.0 (mean= 0.63) favours sedimentary/diagenetic origin. 相似文献
45.
R. Shivashankar M. R. Dheerendra Babu Sitaram Nayak R. Manjunath 《Geotechnical and Geological Engineering》2010,28(5):695-706
This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the
improvement in stiffness, load carrying capacity and resistance to bulging of stone columns installed in soft soils. A new
method of reinforcing the stone columns with vertical nails installed along the circumference of the stone column is suggested
for improving the performance of these columns. Tests were carried out with two types of loading (1) the entire area in the
unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the
limiting axial capacity. It is found that stone columns reinforced with vertical nails along the circumference have much higher
load carrying capacity and undergo lesser compression and lesser lateral bulging as compared to conventional stone columns.
The benefit of vertical circumferential nails increases with increase in the diameter, number and depth of embedment of the
nails. The improvement in the performance of stone column was found to be more significant, even with lower area ratio. It
is found that reinforcing stone column with vertical circumferential nails at the top portion to a depth equal to three times
the diameter of stone columns, will be adequate to prevent the column from excessive bulging and to improve its load carrying
capacity substantially. 相似文献
46.
Sitaram Nayak B. M. Sunil S. Shrihari P. V. Sivapullaiah 《Geotechnical and Geological Engineering》2010,28(6):899-906
To study the impact of salt water intrusion on two types of soils from west coast region of India were investigated in the
laboratory. The key characteristics evaluated included Atterberg limits, compaction characteristics, hydraulic conductivity
and chemical characteristics of selected soils. The sea at this coast receives effluent from different points and hence the
characteristics change with time and locality. Therefore, to maintain uniform composition, 0.5 N sodium chloride solution
(NaCl) was prepared in the laboratory and batch tests were used to determine the immediate effect on soils. Soil specimens
were prepared by mixing the soils with 0.5 N NaCl in the increments of 0, 5, 10 and 20% by weight to vary the degree of contamination.
Experimental results of soils mixed with 0.5 N NaCl showed that the maximum dry density increases and the optimum moisture
content (OMC) decreases with increasing sodium chloride concentration. The study also revealed that the hydraulic conductivity
of the soils tested increases with increase in sodium chloride concentration. The Atterberg limits of contaminated specimens
show a remarkable change when compared with uncontaminated specimens. 相似文献
47.
48.
Prediction of extreme rainfall event using weather pattern recognition and support vector machine classifier 总被引:1,自引:1,他引:0
A major component of flood alert broadcasting is the short-term prediction of extreme rainfall events, which remains a challenging task, even with the improvements of numerical weather prediction models. Such prediction is a high priority research challenge, specifically in highly urbanized areas like Mumbai, India, which is extremely prone to urban flooding. Here, we attempt to develop an algorithm based on a machine learning technique, support vector machine (SVM), to predict extreme rainfall with a lead time of 6–48 h in Mumbai, using mesoscale (20–200 km) and synoptic scale (200–2,000 km) weather patterns. The underlying hypothesis behind this algorithm is that the weather patterns before (6–48 h) extreme events are significantly different from those of normal weather days. The present algorithm attempts to identify those specific patterns for extreme events and applies SVM-based classifiers for extreme rainfall classification and prediction. Here, we develop the anomaly frequency method (AFM), where the predictors (and their patterns) for SVM are identified with the frequency of high anomaly values of weather variables at different pressure levels, which are present before extreme events, but absent for non-extreme conditions. We observe that weather patterns before the extreme rainfall events during nighttime (1800 to 0600Z) is different from those during daytime (0600 to 1800Z) and, accordingly, we develop a two-phase support vector classifier for extreme prediction. Though there are false alarms associated with this prediction method, the model predicts all the extreme events well in advance. The performance is compared with the state-of-the-art statistical technique fingerprinting approach and is observed to be better in terms of false alarm and prediction. 相似文献
49.
James P. Terry Rajeev Lal Sitaram Garimella 《Singapore journal of tropical geography》2011,32(1):102-114
Low‐energy gamma ray spectroscopy has been employed to estimate floodplain sedimentation rates using measurements of 210Pb in floodplain alluvium. The utility of the technique is assessed through the analysis of excess (unsupported) 210Pb profiles in three sediment cores taken from the floodplain of the Labasa River on Vanua Levu in northern Fiji. A low‐energy germanium spectrometer (LEGe) was used for the nondestructive determination of excess 210Pb in a region cultivated intensively with sugarcane. Measured average historical (c. 25 years) vertical accretion rates are between 2.2 and 4.4 cm yr?1. The findings are broadly comparable with published sedimentation rates from analyses of radionuclide profiles elsewhere in the tropical South Pacific Islands, but the rates are higher than those measured previously at the same Labasa River sites using 137Cs profiles. Accelerated soil erosion owing to cane burning and land tillage seems to be largely responsible for sediment production, although flood‐related effects such as channel accretion by coarse bedload and the emplacement of large organic debris also influence floodplain sedimentation. However, application of the 210Pb technique in Fiji (and perhaps neighbouring island countries) is found to have serious drawbacks compared to the more robust 137Cs method, owing principally to the low 210Pb concentrations in the sandy alluvial sediment tested. 相似文献
50.
Bibhuranjan Nayak 《Journal of the Geological Society of India》2011,78(4):345-348
Although sporadic mining of placer gold from river beds is not uncommon in India, there is no documented literature on the
occurrence of gold in the beach placer sand deposits of the country. While characterizing the heavy minerals of the Chavakkad-Ponnani
(CP) beach placer sands along the North Kerala coast, the association of gold with the pyriboles in these sands has been observed.
A native gold grain of about 25 μm was seen to occur as an inclusion within an amphibole of hornblendic composition. The pyriboles
of the CP deposit are angular to sub-angular indicating a nearby provenance that may be in the upstream reaches of the Ponnani
River in the districts of Malappuram and Palakkad or further north in the auriferous tracts of the Wynad-Nilambur or Attapadi
regions. It is argued that the occurrence of native gold in CP deposit is not a freak occurrence and that it warrants thorough
investigation of all the pyribole-ilmenite-rich placers to examine the possible presence of gold and its abundance in the
beach placers of northern Kerala coast. 相似文献