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41.
Comparison of seasonal and intraseasonal variation of tropical climate in NCAR CCM2 GCM with two different cumulus schemes 总被引：4，自引：0，他引：4
K. Rajendran Ravi S. Nanjundiah J. Srinivasan 《Meteorology and Atmospheric Physics》2002,79(1-2):57-86
Summary
The seasonal and intraseasonal variation of tropical climate in National Center for Atmospheric Research (NCAR) Community
Climate Model Version 2 (CCM2) General Circulation Model (GCM) has been examined using two different cumulus parameterization
schemes, the moist convective adjustment scheme of Manabe et al. (1965) and the mass-flux scheme of Hack (1994). Ten-year
simulations have been undertaken with each of these schemes with SST prescribed according to the monthly mean climatology.
The seasonal mean rainfall in the tropics simulated by the moist convective adjustment scheme (MCA) scheme was found to be
more realistic than the mass-flux (Hack) scheme. The more realistic simulation by the MCA scheme was found to be on account
of the fact that the mean moist static energy of the lower troposphere in the MCA scheme was closer to the observations than
in the Hack scheme. In both the schemes, the precipitation in the tropics increases montonically with precipitable water vapour
when the precipitable water vapour is above 40 mm. This is consistent with relationship between precipitation and precipitable
water in the observations. The Hack scheme tends to simulate lower precipitation (for a given amount of precipitable water)
when compared to observations.
The MCA scheme simulates the eastward migration of convective systems along the equator quite well, although the speed of
propagation is somewhat low. The poleward migration of convective systems in the Indian region is more realistically simulated
by the MCA scheme than the Hack scheme. This is because the latitudinal gradient of the mean moist static energy in the MCA
scheme is more realistic than in the Hack scheme. Over most of the tropics, simulation by the MCA scheme is more realistic
on both seasonal and intraseasonal timescales.
Received November 1, 2000 Revised June 20, 2001 相似文献
42.
T. N. Krishnamurti P. Cunningham K. Rajendran 《Meteorology and Atmospheric Physics》2005,88(3-4):237-250
Summary Dramatic examples of forecast failures in global models of moderate resolution (i.e., T106) have been shown to occur during periods of the negative phase of the Pacific/North American (PNA) pattern in the Northern Hemisphere winter. Specifically, in these periods forecast skills at 500hPa as measured by the standard anomaly correlation index dropped to rather low values by days 4 and 5 of the forecasts. This paper examines systematically some of the factors that may have contributed to the failure of these model forecasts.In particular, strong winds approaching intensities on the order of 100ms–1 south of Japan at the 200hPa level were degraded by the initialization and data assimilation procedures of the models. These observed winds were found to be supergradient in nature and representative of the anomalous solution of the gradient wind equation. Procedures such as the multivariate optimum interpolation (with its geostrophic constraints) and the normal-mode initialization including several vertical modes apparently were factors that led to the degradation of these strong winds in the initial model states. In this paper, an analysis of these factors is presented, and it is shown that uninitialized analyses (with no constraints) based on a simple successive correction procedure can retain the strong winds evident in the observations. Forecasts thus performed appear to retain wave trains, a characteristic feature of negative PNA initial states, leading to a significant improvement in forecast skill. 相似文献
43.
Sripriya Rajendran M. NarasimhaA. Dutta M.K. SinhaArun Misra 《International Journal of Mineral Processing》2006
The biased subdivision of slurry feed to a number of unit operations in parallel results in each unit operating under different density volumetric flow rate, feed concentration. Consequently some of the units may operate under sub-optimal conditions leading to reduced operating efficiencies of sizing and cleaning units. The objective of this work was to identify the reasons for biased slurry subdivision in the feed distributor of Washery-II, West Bokaro, Tata Steel, Jamshedpur, India. A lab model of the feed distributor was set up at R&D using the principles of geometric similarity and dynamic similarity. A number of experimental investigations were carried out based on Design Of Experiments and the results analysed using ANOVA. The variation of feed rate of coal and its size distribution through different outlet ports were quantified through two terms, the coal split ratio and the variation index. The design of the insert, the number of water inlets, and the feeding position of coal in the distributor were the most important factors affecting the variation index. In case of coal split ratio, apart from the first two variables, none of the others had a significant effect. Four water inlets with symmetrically arranged outlets, equal water flow rate in the inlets and the material being fed in an annular ring into the distributor was found to reduce both the coal split ratio and the variation index. 相似文献
44.
C.P. Rajendran Kusala Rajendran S. Srinivasalu Vanessa Andrade P. Aravazhi Jaishri Sanwal 《Geoarchaeology》2011,26(6):867-887
Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recent archaeological excavations allude to a sea flood that crippled the ancient port at Kaveripattinam, a trading hub for Southeast Asia, and probably affected the entire South Indian coast, analogous to the 2004 Indian Ocean tsunami impact. We present sedimentary evidence from an archaeological site to validate the textual references to this early medieval event. A sandy layer showing bed forms representing high‐energy conditions, possibly generated by a seaborne wave, was identified at the Kaveripattinam coast of Tamil Nadu, South India. Its sedimentary characteristics include hummocky cross‐stratification, convolute lamination with heavy minerals, rip‐up clasts, an erosional contact with the underlying mud bed, and a landward thinning geometry. Admixed with 1000‐year‐old Chola period artifacts, it provided an optically stimulated luminescence age of 1091 ± 66 yr and a thermoluminescence age of 993 ± 73 yr for the embedded pottery sherds. The dates of these proxies converge around 1000 yr B.P., correlative of an ancient tsunami reported from elsewhere along the Indian Ocean coasts. © 2011 Wiley Periodicals, Inc. 相似文献
45.
The 2001 Mw 7.6 earthquake sourced in the Kachchh rift of northwest India led to extensive damage in the city of Bhuj, located ~70 km southwest of its epicenter. The building stock of this densely populated city was a mix of modern, single, and multistoried structures as well as traditional and non-engineered abodes, most of which were not designed to withstand severe shaking effects. Although there was extensive liquefaction and ground failure in the meizoseismal area, they were not observed in Bhuj, but the damage was severe here. In this study, we apply horizontal to vertical spectral ratio method to ambient vibrations (HVSR-AV) to obtain fundamental resonance frequency (f0) and H/V peak amplitude (A0) to examine if site response had any significant role in the observed damage. The patterns of H/V curves as well as spatial distributions of f0 (0.6–1.4 Hz) and A0 (1.5–4.4) suggest absence of any strong impedance contrast within the subsurface. Similar results obtained for ambient vibrations and earthquake signals suggest the efficacy of the HVSR-AV method as most useful for regions of low-level seismicity. The weathered sandstone that is generally exposed in the city represents the resonating layer whose thickness is approximately estimated as ~66–155 m, based on 1D assumption. The current set of available data precludes any quantitative modeling, but our preliminary inference is that site effects were not significant during the 2001 earthquake damage observed in Bhuj. 相似文献
46.
This study is aimed at using the Empirical Line Method (ELM) to eliminate atmospheric effects with respect to visible and
near infrared bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) and enhanced thematic mapper
plus (ETM+) data. Two targets (Amran limestone as light target and quartz-biotite-sericite-graphite schists as dark target),
which were widely exposed and easy to identify in the imagery were selected. The accuracy of the atmospheric correction method
was evaluated from three targets (vegetation cover, Amran limestone and Akbra shale) of the surface reflectance. Analytical
spectral devices (ASD) FieldSpec3 was used to measure the spectra of target samples. ETM+ data were less influenced by the
atmospheric effect when compared to ASTER data. Normalized differences vegetation indices (NDVI) displayed good results with
reflectance data when compared with digital number (DN) data because it is highly sensitive to ground truth reflectance (GTR).
Most of the differences observed before and after calibration of satellite images (ASTER and ETM+) were absorbed in the SWIR
region.
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