ENSO, IOD and Indian Summer Monsoon in NCEP climate forecast system     

Samir Pokhrel  H. S. Chaudhari  Subodh K. Saha  Ashish Dhakate  R. K. Yadav  Kiran Salunke  S. Mahapatra  Suryachandra A. Rao 《Climate Dynamics》2012,39(9-10):2143-2165

El Ni?o-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Indian Summer Monsoon rainfall features are explored statistically and dynamically using National Centers for Environment Prediction (NCEP) Climate Forecast System (CFSv1) freerun in relation to observations. The 100?years of freerun provides a sufficiently long homogeneous data set to find out the mean state, periodicity, coherence among these climatic events and also the influence of ENSO and IOD on the Indian monsoon. Differences in the occurrence of seasonal precipitation between the observations and CFS freerun are examined as a coupled ocean–atmosphere system. CFS simulated ENSO and IOD patterns and their associated tropical Walker and regional Hadley circulation in pure ENSO (PEN), pure IOD (PIO) and coexisting ENSO-IOD (PEI) events have some similarity to the observations. PEN composites are much closer to the observation as compared to PIO and PEI composites, which suggest a better ENSO prediction and its associated teleconnections as compared to IOD and combined phenomenon. Similar to the observation, the model simulation also show that the decrease in the Indian summer monsoon rainfall during ENSO phases is associated with a descending motion of anomalous Walker circulation and the increase in the Indian summer monsoon rainfall during IOD phase is associated with the ascending branch of anomalous regional Hadley circulation. During co-existing ENSO and IOD years, however, the fate of Indian summer monsoon is dictated by the combined influence of both of them. The shift in the anomalous descending and ascending branches of the Walker and Hadley circulation may be somewhat attributed to the cold (warm) bias over eastern (western) equatorial Indian Ocean basin, respectively in the model. This study will be useful for identifying some of the limitations of the CFS model and consequently it will be helpful in improving the model to unravel the realistic coupled ocean–atmosphere interactions for the better prediction of Indian Summer Monsoon.  相似文献   

Thunderstorms over a tropical Indian station,Minicoy: Role of vertical wind shear     

H. S. Chaudhari  G. K. Sawaisarje  M. R. Ranalkar  P. N. Sen 《Journal of Earth System Science》2010,119(5):603-615

In this study, an attempt has been made to bring out the observational aspects of vertical wind shear in thunderstorms over Minicoy. Case studies of thunderstorm events have been examined to find out the effect of vertical wind shear and instability on strength and longevity of thunderstorms. Role of vertical wind shear in thunderstorms and its mechanism has been explored in this study. Results reveal that for prolonged thunderstorms high and low instability along with moderate to high vertical wind shear (moderate: 0.003 S⁻¹ ≤ vertical wind shear ≤ 0.005 S⁻¹ and high: > 0.005 S⁻¹) play a significant role in longevity and strength of thunderstorms. The mechanism of vertical wind shear in thunderstorms was investigated in a few cases of thunderstorm events where the duration of thunderstorm was covered by the radiosonde/rawin ascent observation taken at Minicoy. Empirical model has been developed to classify thunderstorm type and to determine the strength and longevity of thunderstorms. Model validation has been carried out for selected cases. Model could classify thunderstorm type for most of the cases of thunderstorm events over island and coastal stations.  相似文献   

South Asian summer monsoon precipitation variability: Coupled climate model simulations and projections under IPCC AR4   总被引：6，自引：2，他引：6  

R. H. Kripalani  J. H. Oh  A. Kulkarni  S. S. Sabade  H. S. Chaudhari 《Theoretical and Applied Climatology》2007,90(3-4):133-159

Summary South Asian summer monsoon precipitation and its variability are examined from the outputs of the coupled climate models assessed as part of the Intergovernmental Panel on Climate Change Fourth Assessment. Out of the 22 models examined, 19 are able to capture the maximum rainfall during the summer monsoon period (June through September) with varying amplitude. While two models are unable to reproduce the annual cycle well, one model is unable to simulate the summer monsoon season. The simulated inter-annual variability from the 19 models is examined with respect to the mean precipitation, coefficient of variation, long-term trends and the biennial tendency. The model simulated mean precipitation varies from 500 mm to 900 mm and coefficient of variation from 3 to 13%. While seven models exhibit long-term trends, eight are able to simulate the biennial nature of the monsoon rainfall. Six models, which generate the most realistic 20th century monsoon climate over south Asia, are selected to examine future projections under the doubling CO₂ scenario. Projections reveal a significant increase in mean monsoon precipitation of 8% and a possible extension of the monsoon period based on the multi-model ensemble technique. Extreme excess and deficient monsoons are projected to intensify. The projected increase in precipitation could be attributed to the projected intensification of the heat low over northwest India, the trough of low pressure over the Indo-Gangetic plains, and the land–ocean pressure gradient during the establishment phase of the monsoon. The intensification of these pressure systems could be attributed to the decline in winter/spring snowfall. Furthermore, a decrease of winter snowfall over western Eurasia is also projected along with an increase of winter snowfall over Siberia/eastern Eurasia. This projected dipole snow configuration during winter could imply changes in mid-latitude circulation conducive to subsequent summer monsoon precipitation activity. An increase in precipitable water of 12–16% is projected over major parts of India. A maximum increase of about 20–24% is found over the Arabian Peninsula, adjoining regions of Pakistan, northwest India and Nepal. Although the projected summer monsoon circulation appears to weaken, the projected anomalous flow over the Bay of Bengal (Arabian Sea) will support oceanic moisture convergence towards the southern parts of India and Sri Lanka (northwest India and adjoining regions). The ENSO-Monsoon relationship is also projected to weaken.  相似文献   

Parametric study of site instability due to presence of a weakening shale layer above sloping bedrock     

Sanjeev Kumar  Michael L. Hall 《Geotechnical and Geological Engineering》2004,22(3):361-374

Several areas of St. Louis County, Missouri have been classified as unstable for any type of construction because of the presence of highly plasticity soil/shale on sloping bedrock. These areas have the potential of becoming unstable due to change in any natural condition that can change its moisture content and/or its steepness. One of the structures constructed in this area showed significant movements several years after its construction. The primary goal of this investigation was to analyze site slope configurations in these problematic areas. A parametric study of two site slope profiles, natural and modified, was performed to investigate the effects of various variables such as slope configuration and shale properties, on the stability of a site where potential of site instability exists due to the presence of a shale/clay layer above sloping bedrock. From the results of the parametric study, design charts were developed that incorporate all variables studied in this investigation. These charts will help engineers make informed decisions and help them recognize conditions, which may cause the site slope to become unstable. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Corporate Greening of Foreign Transnationals in Singapore     

Martin Perry  Sanjeev Singh 《Singapore journal of tropical geography》2001,22(1):52-73

The environmental performance of transnational corporations (TNCs) may need to be updated to include evidence of increased corporate environmental responsibility. This is a challenge to geographical perspectives that have been critical of the environmental performance of TNCs. The paper reports the findings of a survey of TNCs with branches in Singapore. Using the survey evidence, TNCs are classified according to their degree of participation in a range of voluntary environmental initiatives. According to the classification, there is a similar proportion of low and high performers but a dominance of medium level activity that can involve little organisational change. A significant association between organisational size and environmental activity is found. Respondents most frequently report that corporate environmental standards motivate environmental action in Singapore. Overall the survey evidence indicates that few TNCs are significantly changing their environmental behaviour. The absence of citizen, NGO and government pressure on TNCs is reducing the extent of voluntary environmental action in Singapore and expectations of widespread corporate greening overlook organisational differences in their opportunity to benefit from investment in environmental management. It is concluded that voluntary corporate environmentalism does not reduce the need for government regulation.  相似文献   

Weathering of dolomite in industrial environments     

K. Lal Gauri  Sanjeev S. Tambe  Emine N. Caner-Saltik 《Environmental Geology》1992,19(1):55-63

To the exclusion of other major atmospheric pollutants, sulfur dioxide is mainly responsible for attack upon dolomite. This article characterizes Laurel Dolomite on the basis of composition, texture, and porosity; describes the mechanism of the SO₂ reaction with dolomite; and develops two equations for the prediction of the rate of decay of dolomite. Over a period of 120 yr nearly 3.57 mm surface reduction at protected areas and 0.915 mm surface reduction at unprotected surfaces of a building in Louisville was calculated. However, these values could not be verified because measurement of these quantities in the field cannot be made.Dr. Caner-Saltik worked at the University of Louisville during her sabbatical leave from Middle East Technical University, Ankara, Turkey from September 1989 to August 1990 as a Fulbright scholar.  相似文献   

Regular spacing of drainage outlets from linear fault blocks   总被引：3，自引：0，他引：3  

Peter J. Talling  Michael D. Stewart  Colin P. Stark  Sanjeev Gupta  & Stephen J. Vincent 《Basin Research》1997,9(4):275-302

Outlets of river basins located on fault blocks often show a regular spacing. This regularity is most pronounced for fault blocks with linear ridge crests and a constant half-width, measured perpendicular to the ridge crest. The ratio of the half-width of the fault block and the outlet spacing is used in this study to characterize the average shape (or spacing ratio) of 31 sets of drainage basins. These fault-block spacing ratios are compared with similar data from small-scale flume experiments and large-scale mountain belts. Fault-block spacing ratios are much more variable than those measured for mountain belts. Differences between fault-block spacing ratios are attributed to variability in factors influencing the initial spacing of channel heads and subsequent rates of channel incision during the early stages of channel network growth (e.g. initial slope and uplift rate, precipitation, runoff efficiency and substrate erodibility). Widening or narrowing of fault blocks during ongoing faulting will also make spacing ratios more variable. It is enigmatic that some of these factors do not produce similar variability in mountain belt spacing ratios. Flume experiments in which drainage networks were grown on static topography show a strong correlation between spacing ratios and surface gradient. Spacing ratios on fault blocks are unaffected by variations in present-day gradients. Drainage basins on the Wheeler Ridge anticline in central California, which have formed on surfaces progressively uplifted by thrust faulting during the last 14 kyr, demonstrate that outlet spacing is likely to be determined during the early stages of drainage growth. This dependency on initial conditions may explain the lack of correlation between spacing ratios of fault blocks and slopes measured at the present day. Spacing ratios determine the location of sediment supply points to adjacent areas of deposition, and hence strongly influence the spatial scale of lateral facies variations in the proximal parts of sedimentary basins. Spacing ratios may be used to estimate this length scale in ancient sedimentary basins if the width of adjacent topography is known. Spacing ratio variability makes these estimates much less precise for fault blocks than for mountain belts.  相似文献   

Evaluation of cloud properties in the NCEP CFSv2 model and its linkage with Indian summer monsoon     

Anupam Hazra  Hemantkumar S. Chaudhari  Ashish Dhakate 《Theoretical and Applied Climatology》2016,124(1-2):31-41

  相似文献   

Seafloor sediment classification from single beam echo sounder data using LVQ network     

Y. Satyanarayana  Sanjeev Naithani  R. Anu 《Marine Geophysical Researches》2007,28(2):95-99

Seafloor sediment classification based on echo characteristics obtained from single-beam echosounder is very useful in remote and instant sediment classification. Results of different classification techniques using such data provide robust results when the acoustic beam has a normal incidence with the seabottom. This may not always be true and show poor classification, with the data acquired during rough sea periods corresponding to both oblique and normal incidence of the acoustic pulse, due to roll and pitch motion of the ship. In the present study, an attempt is made to exploit the artificial neural network (ANN) techniques for better classification with such data. Learning Vector Quantisation (LVQ) is a supervised learning algorithm of ANN that is found to be an effective tool and show good performance. The input data to the network include the roughness index (E1) and hardness index (E2) derived from echo characteristics. The network utilizes the competitive learning, a distance function in the first layer and a linear function in the second layer. The network was tried with a different size of hidden neurons and training data size to see the influence on classification. It is found that with ten neurons in the first layer and four neurons in the second layer good performance in classification for the data was achieved.  相似文献   

Tomographic approach for gas hydrate investigation in Kerala-Konkan region,India     

Naresh Kumar Thakur  Pasupuleti Prasada Rao  N. Vishwanath  Sanjeev Rajput  Bhaskarabhatla Ashalatha 《Marine Geophysical Researches》2007,28(4):373-378

Seismic tomography is an effective means of estimating velocity and structure from multichannel seismic (MCS) reflection data. In this study we have followed a 2D approach to arrive at the probable velocity field configuration from multichannel seismic data and infer the presence of gas hydrates/free-gas in the offshore Kerala-Konkan region, along the eastern part of a seismic line on which a bottom simulating reflector (BSR) has previously been identified. Tomographic modeling consists of the identification of reflection phases and picking of respective travel times for various source-receiver positions. These picks were then utilized to arrive at a 2D velocity field following a forward and inversion approach using a ray tracing technique. The modeling for the first time brought out the finer scale velocity structure under the region of investigation. Modeling through the 2D approach shows lateral variation in velocity field along the studied segment of the seismic line. The results indicate a thin (∼50–60 m) sedimentary cover with velocity ranging from 1,770 to 1,850 m/s. A sedimentary layer with high P-wave velocity 1,980–2,100 m/s below the sea floor was interpreted as the hydrate layer. The thickness of this layer varies between 110 and 140 m. The hydrate layer is underlain by a low-velocity layer having velocities in the range 1,660–1,720 m/s. This low velocity may represent a free gas layer, whose thickness varies between 50 and 100 m located below the hydrated layer. The investigation suggests the occurrence of gas hydrate underlain by free gas in some parts of the Kerala-Konkan offshore region.  相似文献