Variation of Vp/Vs ratios for granitic layers and weekly average number of earthquakes in NE India

Vp/Vs ratios for the granitic layers in Shillong Plateau and the partially overlapping Tezpur seismic area, have been calculated from Wadati diagrams drawn on the basis of seismic phase data. From Shillong plateau the average of 23 readings for some months of 1979 for Vp/Vs is found to be 1.71. For Tezpur area the average of 29 readings of Vp/Vs for 1991-92 is found to be 1.73, but for 1995-96, the average Vp/Vs from 49 readings is found to be 1.68. The overall average from 78 readings for this area is 1.70. The low Vp/Vs for 1995-97 seems to be precursory. For the granitic layer, taking Vp = 5.92 kms/s and Vp/Vs = 1.70. We get Vs=3.48 km/s for NE India. Values of Vp/Vs ratios and number of shocks per day are plotted against time and are shown to undergo sudden lowering before many M³4.2 earthquakes. Vp/Vs is generally lowered below 1.60 in such cases. In Shillong plateau the number of shocks per day for 1979 is found to be three times the number in the adjoining Tezpur area, for 1991-97.

Sulphur study of the Palaeogene coals from Jaintia Hills, Meghalaya, NE India: Implications for palaeoenvironment, utilisation prospects, and environmental impacts

Coal samples of Eocene age (Shella Formation) from four different mines (Bapung, Jaintia, Sutunga, and Lakadong) of the Jaintia Hills of Meghalaya, Northeast India, were collected and investigated to observe the sulphur content and to understand the palaeoenvironment, utilisation prospects, and environmental impact. The study reveals that these coal samples contain sulphur in higher concentration (4.46% to 7.26%) both organic and inorganic forms. There are 3 coal seams exposed in the area. The organic sulphur is higher (2.53%-5.49%) than the inorganic forms (1.26%-1.77%). The upper seam is found to contain higher concentration of sulphur than the lower seam. Intra seam pyritic sulphur also shows an upward increasing trend. The high sulphur content in the coal seams suggests the marine influence in the peat-forming swamps. These coals are classified as High Sulphur coal (>1%) which is the main obstacle in the utilization although high volatile matter and hydrogen content strongly suggest that these coals are good for liquefaction. Moreover, during coal combustion emissions of sulphur dioxide produce acid rain, affecting the environment of the mine areas.

A satellite based study of pre-monsoon thunderstorms (Nor’westers) over eastern India and their organization into mesoscale convective complexes

Nor’wester studies have a long history of climatological, synoptic and radar observations. These studies have been briefly mentioned and the field programs for the study of Nor’westers implemented in India Meteorological Department (IMD) from 1931-1941 have been touched upon. Indian atmospheric science community organized a multi-year STORM program during 2007-2010 to understand the formation of these severe local storms and also understand their dynamics through modeling. An attempt is made to use INSAT Infrared and Visible imageries to document the convective cells which developed over Eastern and North-East (NE) Indian states and adjoining countries of Bangladesh, Bhutan and Nepal for the year 2009. Also convective cells which organized themselves into Mesoscale Convective Complexes (MCCs) for the four years period 2007-2010 have been studied. It is found that by and large Eastern India (Jharkhand, Orissa, Sub Himalayan West Bengal and Bangladesh) is responsible for the initiation of convection. Development occurs as the cells propagate over the neighbouring areas of Bangladesh and NE India. Important observations with regard to initiation, maturity and dissipation etc. of the MCCs are provided. It is suggested that half hourly to hourly monitoring of convection can be accomplished by using INSAT imagery, along with multiple overlapping radar coverages, which could help in nowcasting of convective cells. Synoptic and thermodynamic forcing can help as broad guidance. The only effective way for effective warning is nowcasting using satellite and multiple radar coverage.

A two layer soil moisture model for estimating crop evapotranspiration and runoff

In the present study, a two layer model has been proposed to estimate evapotranspiration, soil moisture storage and runoff. For this purpose soil profile has been assumed to be composed of two layers : the top layer having a fixed field capacity of 100 mm and the underlying layer having field capacity depending on the soil texture. Normal values of rainfall and potential evapotranspiration have been used in the study. The model, applied to kharif and rabi seasons furnishes crop evapotranspiration period when soil in two layers reach wilting point and surface runoff and its duration. The model developed has been applied to 411ocations representing most of the soil types found in India. The analysis revealed that lowest ET is seen over Himalayan foothills and northeast India in kharif and rabi seasons. Enough residual soil moisture is available to the crops at the end of kharif season over NE India; most of it being in the top layer. Eastern India record largest runoff of 800-1000 mm. Arid to semi-arid region in NW India does not seem to experience much runoff.