A Semi-Empirical Approach for Rockfall Prediction Along the Lengpui-Aizawl Highway Mizoram,India

Geotechnical and Geological Engineering - The Lengpui-Aizawl highway in the Northeastern part of India has witnessed several rockfall events in the past decades. This is the only highway that...     

Cause-effect relationships between sea surface temperature, precipitation and sea level along the Bangladesh coast

Summary  The Bangladesh coast, which lies on the confluence of three mighty rivers, the Ganges, the Brahmaputra and the Meghna, with the Himalayas to the north and the Bay of Bengal to the south, is an ideal zone for sea level rise due to enhanced rainfall during the monsoon season from June to September. An attempt has been made here to look into the cause-effect relationships between observed trends in sea surface temperature (SST) over the Bay of Bengal and the trends in monsoon rains and sea level in Bangladesh. The study utilizes the 14-year satellite-derived SSTs over the Bay of Bengal for 1985–1998, the tide gauge stations data along the Bangladesh coast for 1977–1998 and the 31-year monsoon rainfall data for Bangladesh, 1961–1991. Received October 20, 2000     

Mountain range specific analog weather forecast model for northwest Himalaya in India

Mountain range specific analog weather forecast model is developed utilizing surface weather observations of reference stations in each mountain range in northwest Himalaya (NW-Himalaya). The model searches past similar cases from historical dataset of reference observatory in each mountain range based on current situation. The searched past similar cases of each mountain range are used to draw weather forecast for that mountain range in operational weather forecasting mode, three days in advance. The developed analog weather forecast model is tested with the independent dataset of more than 717 days (542 days for Pir Panjal range in HP) of the past 4 winters (2003–2004 to 2006–2007). Independent test results are reasonably good and suggest that there is some possibility of forecasting weather in operational weather forecasting mode employing analog method over different mountain ranges in NW-Himalaya. Significant difference in overall accuracy of the model is found for prediction of snow day and no-snow day over different mountain ranges, when weather is predicted under snow day and no-snow day weather forecast categories respectively. In the same mountain range, significant difference is also found in overall accuracy of the model for prediction of snow day and no-snow day for different areas. This can be attributed to their geographical position and topographical differences. The analog weather forecast model performs better than persistence and climatological forecast for day-1 predictions for all the mountain ranges except Karakoram range in NW-Himalaya. The developed analog weather forecast model may help as a guidance tool for forecasting weather in operational weather forecasting mode in different mountain ranges in NW-Himalaya.     

Bianchi type-II space-times with constant deceleration parameter in self creation cosmology

The properties of locally rotationally symmetric Bianchi type-II perfect fluid space-times are analyzed in Barber’s second self-creation theory by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration parameter. By assuming the equation of state p=γ ρ, many new solutions are obtained for different era—Zel’dovich, radiation, vacuum and vacuum energy dominated. The solutions with power-law and exponential expansion are discussed. A detailed study of geometrical and physical parameters is carried out. The nature of singularity is also clarified in each case.     

Sea Level Changes Along Bangladesh Coast in Relation to the Southern Oscillation Phenomenon

Interannual variations of sea level along the Bangladesh coast are quite pronounced and often dominate the long-term sea level trends that are taking place. The El Niño/Southern Oscillation (ENSO) induced variation is an important component of interannual mode of variations. The present article deals with the relationship between the sea level variations along the Bangladesh coast and the Southern Oscillation phenomenon. The mean tide level data of monsoon season (June to September) pertaining to Hiron Point (in Sundarbans) and Char Changa (on the mouth of Meghna River) have been analyzed and correlated to the Southern Oscillation Index (SOI). The annual variation of mean tide level in the coastal areas of Bangladesh reveals that the tide level reaches its peak during the monsoon season. The maximum tide level during the calendar year is recorded in August. Thus, it is not surprising that the inundation of the coastal belt of Bangladesh due to the floods is most common during the summer monsoon season, especially from July to September. Therefore, the sea level variations during the monsoon are of paramount importance to Bangladesh. The results of the present study show that both at Hiron Point and Char Changa there is a substantial difference between the mean tide level during the El Niño and La Niña monsoons. The mean tide level at Hiron Point is higher by about 5 cm during August of La Niña years as compared to that during the El Niño years. The difference at Char Changa, which is located at the mouth of Meghna River, is much higher. This is probably due to the increased fresh water discharge into the Meghna River during La Niña years. Thus at the time of crossing of a monsoon depression, the chances of widespread inundation are higher during a La Nin~a year as compared to that during an El Niño year. The Correlation Coefficients (CCs) between Mean Tide Levels (MTLs) at Hiron Point and Char Changa and the SOI during September (at the end of monsoon) are +0.33 and +0.39 respectively. These CCs are statistically significant at 90% and 95% levels, respectively. These results may find applications in the preparedness programs for combating sea level associated disasters in Bangladesh.     

Precipitation-runoff simulation for a Himalayan River Basin, India using artificial neural network algorithms

In the Himalayan regions, precipitation-runoff relationships are amongst the most complex hydrological phenomena, due to varying topography and basin characteristics. In this study, different artificial neural networks (ANNs) algorithms were used to simulate daily runoff at three discharge measuring sites in the Himalayan Kosi River Basin, India, using various combinations of precipitation-runoff data as input variables. The data used for this study was collected for the monsoon period (June to October) during the years of 2005 to 2009. ANNs were trained using different training algorithms, learning rates, length of data and number of hidden neurons. A comprehensive multi-criteria validation test for precipitation-runoff modeling has been undertaken to evaluate model performance and test its validity for generating scenarios. Global statistics have demonstrated that the multilayer perceptron with three hidden layers (MLP-3) is the best ANN for basin comparisons with other MLP networks and Radial Basis Functions (RBF). Furthermore, non-parametric tests also illustrate that the MLP-3 network is the best network to reproduce the mean and variance of observed runoff. The performance of ANNs was demonstrated for flows during the monsoon season, having different soil moisture conditions during period from June to October.     

Interaction of the WAT Source in A3395 with the Intracluster Medium

Using X-ray observations from Chandra and XMM-Newton and radio observations from the Australia Telescope Compact Array (ATCA), we have examined the merging environment of the bimodal cluster Abell 3395. From X-ray data we have produced thermodynamic maps of the cluster. The Wide Angle Tail (WAT) galaxy seen in the radio is slightly offset from the X-ray emission peak of the southern part of the cluster. The unsharp masked Chandra image of the cluster does not show any deficit in the X-ray flux near the location of the source possibly because the thermal plasma has leaked into the cavities.     

The two-component extreme value distribution for flood frequency analysis: Derivation of a new estimation method

The two component extreme value (TCEV) distribution has recently been shown to account for most of the characteristics of the real flood experience. A new method of parameter estimation for this distribution is derived using the principle of maximum entropy (POME). This method of parameter estimation is suitable for application in both the site-specific and regional cases and appears simpler than the maximum likelihood estimation method. Statistical properties of the regionalized estimation were evaluated using a Monte Carlo approach and compared with those of the maximum likelihood regional estimators.     

Assessment of Potential Alkali Aggregate Reactivity for Siliceous and Carbonate Aggregates: A Case Study

Alkali-aggregate reactivity (AAR) involves a reaction between the pore solution of concrete and certain minerals found in some aggregates. To assess the potential AAR various physical and chemical tests are available and extensively used. The petrographic examination is the initial assessment that decides the further investigation for potential reactivity of an aggregate. A chemical approach is another option to assess the aggregate for potential AAR. The accelerated mortar bar method and concrete prism tests are other very important tests for determination of potential AAR of aggregates samples. However, a combination of the results of all the techniques provides most reliable results for potential AAR in aggregates. Moreover, each test represents the stepwise investigation and provides the decision for the test of next approach. Petrographic examination and chemical test methods are the quick decision-making methods for the estimation of potential AAR. In some cases, by these two methods, the aggregate can be selected and rejected confidently. However, for critical values or doubtful aggregates, further tests are necessary to develop a higher confidence level of the results. The present study comprises of the assessment of the alkali-reactivity of siliceous and carbonate aggregates using petrographic and chemical approaches. X-ray diffraction analysis was used as a complementary method to the petrographic evaluation. Moreover, under chemical approach, two separate test methods were used for siliceous and carbonate aggregates. The study also included a comparison between the petrographic examination and chemical analysis for the same aggregate samples and found significant results.