Concurrent Use of OSCAT and AltiKa to Characterize Antarctic Ice Surface Features

Radar altimetry provides an important geophysical parameter, backscatter coefficient (σ₀), which is useful in studying target surface characteristics. Ku-band (Oceansat-2 scatterometer- OSCAT) and Ka-band (SARAL-AltiKa altimeter) data are concurrently used to characterize polar surface features over the Antarctic region. Maximum-likelihood classification has been employed to classify combined data set (AltiKa and OSCAT) for discrimination among sea ice, open water, and ice sheet (interior and exterior). The sea ice region obtained using the current approach has been compared with sea ice boundary derived from passive microwave data.     

Measurement of radon exhalation rate in various building materials and soil samples

Indoor radon is considered as one of the potential dangerous radioactive elements. Common building materials and soil are the major source of this radon gas in the indoor environment. In the present study, the measurement of radon exhalation rate in the soil and building material samples of Una and Hamirpur districts of Himachal Pradesh has been done with solid state alpha track detectors, LR-115 type-II plastic track detectors. The radon exhalation rate for the soil samples varies from 39.1 to 91.2 mBq kg^?1 h^?1 with a mean value 59.7 mBq kg^?1 h^?1. Also the radium concentration of the studied area is found and it varies from 30.6 to 51.9 Bq kg^?1 with a mean value 41.6 Bq kg^?1. The exhalation rate for the building material samples varies from 40.72 (sandstone) to 81.40 mBq kg^?1 h^?1 (granite) with a mean value of 59.94 mBq kg^?1 h^?1.     

Debris flow susceptibility zonation using statistical models in parts of Northwest Indian Himalayas—implementation,validation, and comparative evaluation

Natural Hazards - Debris flows are natural disasters with devastating consequences and frequent recurrence in changing climatic regime of the Indian Himalayas. Therefore, it is necessary to...     

MST radar investigation on inertia-gravity waves associated with tropical depression in the upper troposphere and lower stratosphere over Gadanki (13.5°N, 79.2°E)

Continuous measurements of 3-dimensional winds, spectral parameters, and tropopause height for ～114 h during the passage of a tropical depression using mesosphere–stratosphere–troposphere (MST) radar at Gadanki (13.5°N, 79.2°E) are discussed. The spectral analysis of zonal and meridional winds shows the presence of inertia-gravity wave (IGW) with the dominant periodicity of 56 h and intrinsic period of 27 h in the upper troposphere and lower stratosphere (UTLS). The strengthening of easterly jet and associated wind shears during the passage of the depression is one of the causative mechanisms for exciting the IGW. A well-established radar method is used to identify the tropopause and to study its response to the propagating atmospheric disturbances. The significance of the present study lies in showing the response of tropopause height to the IGW during tropical depression for the first time, which will have implications in stratosphere–troposphere exchange processes.     

Assessment of Indian summer monsoon simulation by Community Atmosphere Model (CAM3)

Seasonal prediction of Indian Summer Monsoon (ISM) has been attempted for the current year 2011 using Community Atmosphere Model (CAM) developed at the National Centre for Atmospheric Research (NCAR). First, 30?years of model climatology starting from 1981 to 2010 has been generated to capture the variability of ISM over the Indian region using 30 seasonal simulations. The simulated model climatology has been validated with different sets of observed climatology, and it was observed that the simulated climatological rainfall is affected by model bias. Subsequently, a bias correction procedure using the Tropical Rainfall Measuring Mission (TRMM) 3B43 rainfall has been proposed. The bias-corrected rainfall climatology shows both spatial and temporal variability of ISM satisfactorily. Further, four sets of 10-member ensemble simulations of ISM 2009 and 2010 have been performed in hindcast mode using observed sea surface temperature (SST) and persistence of April SST anomaly, and it has been found that the bias-corrected model rainfall captures the seasonal variability of ISM reasonably well with some discrepancies in these two contrasting monsoon years. With this positive background, the seasonal prediction of ISM 2011 has been carried out in forecast mode with the assumption of persistence of May SST anomaly from June through September 2011. The model assessment shows an 11% deficiency in All-India Rainfall (AIR) of ISM 2011. In particular, the monthly accumulated rains are predicted to be 101% (17.6?cm), 86% (24.3?cm), 83% (21.0?cm) and 95% (15.5?cm) of normal AIR for the months of June, July, August and September, respectively.     

Use of SARAL/AltiKa Observations for Modeling River Flow

In the absence of many gauging stations in the major and mighty river systems, there is a need for satellite-based observations to estimate temporal variations in the river water storage and associated water management. In this study, SARAL/AltiKa application for setting up hydraulic model (HEC-RAS) and river flow simulations over Tapi River India has been discussed. Waveform data of 40 Hz from Ka band altimeter has been used for water levels retrieval in the Tapi river. SARAL/AltiKa retrieved water levels were converted to discharge in the upstream location (track-926) using the rating curve available for the nearby gauging site and using linear spatial interpolation technique. Steady state simulations were done for various flow conditions in the upstream. Validation of river flow model was done in the downstream location (track-367) by comparing simulated and altimeter retrieved water levels (RMSE 0.67 m). Validated model was used to develop rating curve between water levels and simulated discharge for the downstream location which enables to monitor discharge variations from satellite platform in the absence of in situ observations. It has been demonstrated that SARAL/AltiKa data has potential for river flow monitoring and modeling which will feed for flood disaster forecasting, management and planning.     

Response and capacity of monopod caisson foundation under eccentric lateral loads

Monopod caisson foundation is a viable alternative for supporting offshore wind turbines located at shallow water depths. This foundation system has to resist overturning moment generated due to resultant lateral load, arising from wind and water wave action, that can act at any loading height above the seabed. This paper presents results of a numerical investigation performed to determine the influence of loading height, caisson geometry and superstructure load on the ultimate lateral capacity, initial stiffness, and soil failure zone of the foundation, when installed in very dense sand. Both the ultimate and serviceable states of the caisson foundation obtained from the analyses are represented in terms of envelopes plotted between lateral load and overturning moment. Simplified expressions, which take into account the influence of caisson geometry, loading height, and soil properties, are also presented to serve as a preliminary base for design of the monopod caisson foundation.     

Physical and biological response of the Arabian Sea to tropical cyclone Phyan and its implications

The response to the tropical cyclone Phyan, which developed in the eastern Arabian Sea during 9-11 November 2009, was rapid cooling of sea surface temperature (SST), enhancement of chlorophyll a and two-fold increase in net primary productivity (NPP). Cooling of SST was immediate in response to the strong wind-mixing, and the subsequent upward Ekman pumping sustained the cooling even after the dissipation of Phyan. The biological response mediated by the upward Ekman pumping driven vertical transport of subsurface nutrient showed a time lag of 3-4 days. The CO? flux to the atmosphere associated with Phyan was 0.123 Tg C, which accounted for ~85% of the total out-gassing from the eastern Arabian Sea during November. Thus, an increased occurrence of cyclones in a warming environment will lead to an enhanced biomass production and also increase in CO? out-gassing.