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121.
Sanjay Kumar Mehta M. Venkat Ratnam B.V. Krishna Murthy 《Journal of Atmospheric and Solar》2011,73(17-18):2462-2473
The characteristics of the cold point tropopause (CPT), convective tropopause (COT) and tropical tropopause layer (TTL) in the tropical region at different longitudes are studied using radiosonde data at 5 stations in the tropical belt (±15°) and high resolution GPS radiosonde data from April 2006 to December 2008 at Gadanki (13.5°N, 79.2°E) also a tropical station. The CPT over Gadanki is found to be higher than over the rest of the stations. This aspect is further confirmed using COSMIC GPS RO observations. In the Northern Hemisphere (NH) winter, the CPT is coldest over stations in the Pacific region compared to the other stations while in the NH summer, it is coldest at Gadanki, a station in the Indian monsoon region. The range of seasonal variation of the CPT temperature is found to be quite small over Gadanki compared to the other stations whereas that of the CPT altitude is nearly the same. 相似文献
122.
M. Venkat Ratnam M. Roja Raman Sanjay Kumar Mehta Debashis Nath B.V. Krishnamurthy M. Rajeevan S. Vijaya Bhaskara Rao D. Narayana Rao 《Journal of Atmospheric and Solar》2011,73(7-8):731-740
To investigate the sub-daily variation in Tropical Easterly Jet (TEJ), a few special experiments have been conducted with mesosphere–stratosphere–troposphere (MST) radar located at Gadanki(13.5°N, 79.2°E) under Study on Atmospheric Forcing and Responses (SAFAR) campaign during 2008–2009. Large sub-daily changes in the TEJ characteristics are observed within a day in addition to day-to-day changes. Based on this observational study, three possible mechanisms for the sub-daily variations are proposed i.e., (1) motion of TEJ core, (2) large updrafts and downdrafts, and (3) strong wave activity. Interestingly, TEJ peak altitude is seen above the Cold Point Tropopause altitude for about 42% of the days. 相似文献
123.
Simultaneous Estimation of Geologic and Reservoir State Variables Within an Ensemble-Based Multiple-Point Statistic Framework 总被引:1,自引:1,他引:0
Liangping Li Sanjay Srinivasan Haiyan Zhou J. Jaime Gómez-Hernández 《Mathematical Geosciences》2014,46(5):597-623
Assessment of uncertainty due to inadequate data and imperfect geological knowledge is an essential aspect of the subsurface model building process. In this work, a novel methodology for characterizing complex geological structures is presented that integrates dynamic data. The procedure results in the assessment of uncertainty associated with the predictions of flow and transport. The methodology is an extension of a previously developed pattern search-based inverse method that models the spatial variation in flow parameters by searching for patterns in an ensemble of reservoir models. More specifically, the pattern-searching algorithm is extended in two directions: (1) state values (such as piezometric head) and parameters (such as conductivities) are simultaneously and sequentially estimated, which implies that real-time assimilation of dynamic data is possible as in ensemble filtering approaches; and (2) both the estimated parameter and state variables are considered when pattern searching is implemented. The new scheme results in two main advantages—better characterization of parameters, especially for delineating small scale features, and an ensemble of head states that can be used to update the parameter field using the dynamic data at the next instant, without running expensive flow simulations. An efficient algorithm for pattern search is developed, which works with a flexible search radius and can be optimized for the estimation of either large- or small-scale structures. Synthetic examples are employed to demonstrate the effectiveness and robustness of the proposed approach. 相似文献
124.
In this note, we compare the LiNbO3 and Piezo-Electrically(PE) servo controlled air gap Fabry-Perot etalons for observing the Sun. An identical test setup was
used to evaluate the instrumental parameters of the two etalons. It is found that for the etalons with similar finesse the
advantage of using PE Etalons is tunability over entire Free Spectral Range. On the other hand, the LiNbO3 etalons have advantage of wider acceptance angle.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
125.
Sanjay Jain 《Journal of Astrophysics and Astronomy》1997,18(4):363-379
In a universe whose elementary constituents are point particles there does not seem to be any obvious mechanism for avoiding
the initial singularities in physical quantities in the standard model of cosmology. In contrast in string theory these singularities
can be absent even at the level where spacetime is treated classically. This is a consequence of the basic degrees of freedom
of strings in compact spaces, which necessitate a reinterpretation of what one means by a very small universe. We discuss
the basic degrees of freedom of a string at the classical and quantum level, the minimum size of strings (string uncertainty
principle), the t-duality symmetry, and string thermodynamics at high energy densities, and then describe how these considerations
suggest a resolution of the initial singularity problem. An effort has been made to keep this writeup self-contained and accessible
to non-string theorists. 相似文献
126.
Natural Hazards - The precise focal depth of earthquakes is a crucial parameter for better characterising of complex tectonic zones, especially where seismogenic faults occur at different depths.... 相似文献
127.
Pallabee Choudhury Kalpna Gahalaut Rakesh Dumka V. K. Gahalaut Abhay Kumar Singh Sanjay Kumar 《Environmental Earth Sciences》2018,77(22):770
A continuous GPS measurement site, ISRR, at Gandhinagar (Western India), documented ~?5 mm/year of surface subsidence rate during 2009–2016. Preliminary modelling using an analytical solution indicates that the observed surface subsidence rate at the ISRR site is consistent with the ground water depletion reported from Gandhinagar. An assessment of data from GPS sites at Lucknow and Varanasi in the Indo-Gangetic plains in Northern India does not indicate any significant subsidence at these sites which is also consistent with the in situ observations of insignificant depletion of ground water in the region. 相似文献
128.
129.
A geomorphological instantaneous unit hydrograph (GIUH) is derived from the geomorphological characteristics of a catchment and it is related to the parameters of the Clark instantaneous unit hydrograph (IUH) model as well as the Nash IUH model for deriving its complete shape. The developed GIUH based Clark and Nash models are applied for simulation of the direct surface run‐off (DSRO) hydrographs for ten rainfall‐runoff events of the Ajay catchment up to the Sarath gauging site of eastern India. The geomorphological characteristics of the Ajay catchment are evaluated using the GIS package, Integrated Land and Water Information System (ILWIS). The performances of the GIUH based Clark and Nash models in simulating the DSRO hydrographs are compared with the Clark IUH model option of HEC‐1 package and the Nash IUH model, using some commonly used objective functions. The DSRO hydrographs are computed with reasonable accuracy by the GIUH based Clark and Nash models, which simulate the DSRO hydrographs of the catchment considering it to be ungauged. Inter comparison of the performances of the GIUH based Clark and Nash models shows that the DSRO hydrographs are estimated with comparable accuracy by both the models. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
130.
The present paper analyzes the dual frequency signals from GPS satellites recorded at Varanasi (Geographic latitude 25°, 16′ N,
longitude 82°, 59′ E) near the equatorial ionization anomaly (EIA) crest in India, to study the effect of geomagnetic storm
on the variation of TEC, during the low solar active period of May 2007 to April 2008. Three most intense—but still moderate
class—storms having a rapid decrease of Dst-index observed during the GPS recorded data have been analyzed, which occurred on 20 November 2007, 9 March 2008 and 11 October
2008 were selected and storm induced features in the vertical TEC (VTEC) have been studied considering the mean VTEC value
of quiet days as reference level. The possible reasons for storm time effects on VTEC have been discussed in terms of local
time dependence, storm wind effect as well as dawn-dusk component of interplanetary electric field (IEF) Ey intensity dependence. 相似文献