排序方式： 共有26条查询结果，搜索用时 15 毫秒
1.
2.
Hemantkumar S. Chaudhari Samir Pokhrel Sachiko Mohanty Subodh K. Saha 《Theoretical and Applied Climatology》2013,114(3-4):459-477
This study has identified probable factors that govern ISMR predictability. Furthermore, extensive analysis has been performed to evaluate factors leading to the predictability aspect of Indian Summer Monsoon Rainfall (ISMR) using uncoupled and coupled version of National Centers for Environmental Prediction Coupled Forecast System (CFS). It has been found that the coupled version (CFS) has outperformed the uncoupled version [Global Forecast System (GFS)] of the model in terms of prediction of rainfall over Indian land points. Even the spatial distribution of rainfall is much better represented in the CFS as compared to that of GFS. Even though these model skills are inadequate for the reliable forecasting of monsoon, it imparts the capacious knowledge about the model fidelity. The mean monsoon features and its evolution in terms of rainfall and large-scale circulation along with the zonal and meridional shear of winds, which govern the strength of the monsoon, are relatively closer to the observation in the CFS as compared to the GFS. Furthermore, sea surface temperature–rainfall relation is fairly realistic and intense in the coupled version of the model (CFS). It is found that the CFS is able to capture El Niño Southern Oscillation ISMR (ENSO-ISMR) teleconnections much strongly as compared to GFS; however, in the case of Indian Ocean Dipole ISMR teleconnections, GFS has the larger say. Coupled models have to be fine-tuned for the prediction of the transition of El Niño as well as the strength of the mature phase has to be improved. Thus, to sum up, CFS tends to have better predictive skill on account of following three factors: (a) better ability to replicate mean features, (b) comparatively better representation of air–sea interactions, and (c) much better portrayal of ENSO-ISMR teleconnections. This study clearly brings out that coupled model is the only way forward for improving the ISMR prediction skill. However, coupled model’s spurious representation of SST variability and mean model bias are detrimental in seasonal prediction. 相似文献
3.
4.
The rocks exposed in the area around Kuanthal represent one of the oldest Precambrian formations of India and constitute the Banded Gneissic Complex (B.G.C.) of Heron (1953). The main rock types are staurolite-sillimanite schists/gneisses, sillimanite gneisses with or without K-feldspar, migmatites and amphibolites, often intimately and inextricably mixed up with one another. The petrochemical studies of the metapelitic rocks show that the formation of sillimanite is controlled by parent rock chemistry. The critical controlling parameters area: alumina, alkalies (Na2O + K2O) and oxidation ratio of rocks. These criteria are equally valid for other well-known areas of high-grade metamorphism. The validity of this proposition has been tested by statistical methods such as multivariate analysis and Mahalonbis's generalized distance D2. The linear discriminant function controlling sillimanite paragenesis in metapelites has been worked out and an equation has been evolved to delineate the ‘SB’ (sillimanite-bearing) and ‘SF’ (sillimanite-free) rocks. 相似文献
5.
The latest version of the state-of-the-art global land–atmosphere–ocean coupled climate forecast system of NCEP has shown considerable improvement in various aspects of the Indian summer monsoon. However, climatological mean dry bias over the Indian sub-continent is further increased as compared to the previous version. Here we have attempted to link this dry bias with climatological mean bias in the Eurasian winter/spring snow, which is one of the important predictors of the Indian summer monsoon rainfall (ISMR). Simulation of interannual variability of the Eurasian snow and its teleconnection with the ISMR are quite reasonable in the model. Using composite analysis it is shown that a positive snow anomaly, which is comparable to the systematic bias in the model, results into significant decrease in the summer monsoon rainfall over the central India and part of the Equatorial Indian Ocean. Decrease in the summer monsoon rainfall is also found to be linked with weaker northward propagation of intraseasonal oscillation (ISO). A barotropic stationary wave triggered by positive snow anomaly over west Eurasia weakens the upper level monsoon circulation, which in turn reduces the zonal wind shear and hence, weakens the northward propagation of summer monsoon ISOs. A sensitivity experiment by reducing snow fall over Eurasian region causes decrease in winter and spring snow depth, which in turn leads to decrease in Indian summer monsoon rainfall. Results from the sensitivity experiment corroborate with those of composite analysis based on long free run. This study suggests that further improvements in the snow parametrization schemes as well as Arctic sea ice are needed to reduce the Eurasian snow bias during winter/spring, which may reduce the dry bias over Indian sub-continent and hence predictability aspect of the model. 相似文献
6.
Suresh C. Patel Rajiv Khalkho Subhagya K. Patel Janisar M. Sheikh Duryadhan Behera Sanjeev Chaudhari Naraga Prabhakar 《Environmental Earth Sciences》2014,72(6):2033-2049
Incidence of high fluoride (F?) in groundwater (>1.5 mg/L) in two tribal belts of eastern India, one around Chukru in the Palamau district of Jharkhand and the other around Karlakot in the Nuapada district of Odisha, has been studied. The maximum concentration of F? in groundwater from dug wells and tube wells is 10.30 mg/L in Chukru and 4.62 mg/L in Karlakot. The groundwaters are mildly alkaline with pH ranges of 7.52–8.22 and 7.33–8.20 in Chukru and Karlakot, respectively. The F? concentration is positively correlated with pH, electrical conductivity and SO4 2? in both areas. The high F? in groundwater resulted mainly from dissolution of biotite and fluorapatite in quartzofeldspathic gneiss. The ionic dominance pattern (in meq/L) is mostly in the order Ca2+ > Na+ > Mg2+ > K+ among cations and HCO3 ? > SO4 2? > < Cl? > F? among anions in the Karlakot groundwater. Preliminary adsorption experiments were conducted on natural haematite iron ore and synthetic magnetite to evaluate their potential for F? removal from water. Effects of different parameters such as contact time, pH, adsorbent dose and initial F? concentration on the adsorption capacity of these materials were investigated. Strong dependence of F? removal on pH was observed for both the adsorbents. With natural haematite iron ore, the maximum F? removal of 66 % occurred at an initial pH of 3.2 for a solution with F? concentration of 3 mg/L, adsorbent dose of 7 g/L and overnight contact time. The haematite iron ore was observed to increase the pH of the F? solution. Adsorption equilibrium was not achieved with this adsorbent even after a contact time of 45.2 h. In the case of synthetic magnetite, 84 % F? removal was achieved after 2 min of contact time for a solution with F? concentration of 6 mg/L, adsorbent dose of 10 g/L and initial pH of 7. The results indicate high potential of both natural haematite iron ore and synthetic magnetite as adsorbents of F? in water. 相似文献
7.
8.
Mahadevappa Naganathappa Shivaji Waghmare Ajay Chaudhari 《Astrophysics and Space Science》2011,332(2):249-256
This work reports theoretical infrared and electronic absorption spectra of formaldehyde and its ions in gas phase and H2O ice at different levels of theory. The vibrational frequencies from this work at B3LYP/6-311++G** level are in agreement with the experimental determinations. The gas phase dipole moment of neutral formaldehyde 2.4 D is
in excellent agreement with the experimental value of 2.33 D. An influence of ice on vibrational frequencies of neutral formaldehyde
molecule was obtained using Self Consistence Isodensity Polarizable Continuum Model (SCI-PCM) with dielectric constant 78.5.
Significant shift in vibrational frequencies for neutral formaldehyde molecule when studied in H2O ice and upon ionization is observed. All the vibrational modes in cation and anion of formaldehyde in gas phase are red
shifted than the corresponding modes in neutral formaldehyde. Two vibrational modes are blue shifted and all other modes are
red shifted for neutral formaldehyde in H2O ice. Time dependent density functional theory (TDDFT) is used to study electronic absorption spectrum of neutral formaldehyde
and its charged states. It is found that like neutral formaldehyde, its cation and anion also display strong σ→σ
∗ electronic transitions in vacuum and far UV regions. This study should help in detecting formaldehyde molecule and its ions
in gas phase and in H2O ice in different astronomical environment. 相似文献
9.
J. S. Chowdary H. S. Chaudhari C. Gnanaseelan Anant Parekh A. Suryachandra Rao P. Sreenivas S. Pokhrel P. Singh 《Climate Dynamics》2014,42(7-8):1925-1947
This study investigates the El Niño Southern Oscillation (ENSO) teleconnections to tropical Indian Ocean (TIO) and their relationship with the Indian summer monsoon in the coupled general circulation model climate forecast system (CFS). The model shows good skill in simulating the impact of El Niño over the Indian Oceanic rim during its decay phase (the summer following peak phase of El Niño). Summer surface circulation patterns during the developing phase of El Niño are more influenced by local Sea Surface Temperature (SST) anomalies in the model unlike in observations. Eastern TIO cooling similar to that of Indian Ocean Dipole (IOD) is a dominant model feature in summer. This anomalous SST pattern therefore is attributed to the tendency of the model to simulate more frequent IOD events. On the other hand, in the model baroclinic response to the diabatic heating anomalies induced by the El Niño related warm SSTs is weak, resulting in reduced zonal extension of the Rossby wave response. This is mostly due to weak eastern Pacific summer time SST anomalies in the model during the developing phase of El Niño as compared to observations. Both eastern TIO cooling and weak SST warming in El Niño region combined together undermine the ENSO teleconnections to the TIO and south Asia regions. The model is able to capture the spatial patterns of SST, circulation and precipitation well during the decay phase of El Niño over the Indo-western Pacific including the typical spring asymmetric mode and summer basin-wide warming in TIO. The model simulated El Niño decay one or two seasons later, resulting long persistent warm SST and circulation anomalies mainly over the southwest TIO. In response to the late decay of El Niño, Ekman pumping shows two maxima over the southern TIO. In conjunction with this unrealistic Ekman pumping, westward propagating Rossby waves display two peaks, which play key role in the long-persistence of the TIO warming in the model (for more than a season after summer). This study strongly supports the need of simulating the correct onset and decay phases of El Niño/La Niña for capturing the realistic ENSO teleconnections. These results have strong implications for the forecasting of Indian summer monsoon as this model is currently being adopted as an operational model in India. 相似文献
10.
The seasonal variation of lightning flash activity over the Indian subcontinent (0°N–35°N and 60°E–100°E) is studied using the quality checked monthly lightning flash data obtained from lightning imaging sensor on board the Tropical Rainfall Measuring Mission satellite. This paper presents results of spatio-temporal variability of lightning activity over the Indian subcontinent. The study of seasonal total lightning flashes indicates that the lightning flash density values are in qualitative agreement with the convective activity observed over this region. Maximum seasonal total flash counts are observed during the monsoon season. The propagation of the inter-tropical convergence zone over this region is also confirmed. Synoptic conditions responsible for variation of lightning activity are also investigated with the help of an observed dataset. The mean monthly flash counts show a peak in the month of May, which is the month of maximum temperatures over this region. Maximum flash density (40.2 km?2 season?1) is observed during the pre-monsoon season at 25.2°N/91.6°E and the annual maximum flash density of 28.2 km?2 year?1 is observed at 33.2°N/74.6°E. The study of the inter-annual variability of flash counts exhibits bimodal nature with the first maximum in April/May and second maximum in August/September. 相似文献