Intercomparison of High-Resolution Bay of Bengal Circulation Models Forced with Different Winds

The high-resolution Bay of Bengal circulation modeling in the region [80E–95E; 5N–22N] is performed with a horizontal resolution of 10 km and the highest vertical resolution of 5 m near the surface. The intercomparison experiments, with ocean model forced with the near-surface (1) National Centers for Environmental Prediction (NCEP) reanalysis winds and (2) blended seawinds data (a combination of remotely sensed scatterometer and in situ observations) are carried out for a period of 17 years during 1998–2014. The seasonal variability of the realistically simulated surface hydrographic (temperature and salinity) and circulation (currents) variables from both the experiments is compared and contrasted with the observational data. The mixed layer depth seasonal variability of the region is also studied. The mesoscale features of currents at 50 and 100 m are also studied. The volume transport across different sections in the Bay of Bengal is computed and its relation with summer monsoon rainfall is investigated. The results suggest that there is no real advantage of using high-resolution blended seawinds over the much coarser NCEP reanalysis winds.     

Crustal structure in the North Arabian Sea from magnetic surveys

The spectral study of the aero-magnetic map of the North Arabian Sea (above 20°N) has delineated three horizons at average depths of 45 km, 21 km, and 8 km. Spectral estimates from smaller blocks of data drawn from the original map suggest that the 21 km horizon varies in depth from 14 km on the abyssal plain (oceanic crust) to 24 km towards the north and 28 km towards the east onto the continental shelf. This appears to correspond to the crust-mantle interface (Moho). The 8 km horizon corresponds to the top of the igneous basement. The significance of the deepest layer (45 km) is discussed as the maximum depth of the Curie point geotherm in this region. The spectral estimate of the block of data on the continental shelf off the west coast of India (above 20°N) has brought out some magnetic inhomogeneity at a shallower depth of 4 km. This appears to be connected with the sea-floor spreading phenomenon from the Carlsberg ridge. The presence of such a magnetic inhomogeneity at a depth of 4 km is further confirmed by the spectral estimate of a marine magnetic map off the west coast of India around Bombay. The depth of the basement inferred from this study is in close agreement with that obtained from other studies in this region, such as seismics.     

Total column ozone retrieval using INSAT-3D sounder in the tropics: A simulation study

The present study examines the potential of infrared sounder observations from Indian geostationary satellite INSAT-3D for the estimation of total column integrated ozone over the tropical Indian region. A dataset with diverse profiles was used to create training and testing datasets using forward simulations from a radiative transfer model for infrared sounder channels. A study was carried out for the standard tropical atmospheric profile to examine the sensitivity of ozone band radiance corresponding to the atmospheric temperature, water vapour, and ozone mixing ratios at different atmospheric pressure levels. Further, statistical retrieval technique has been used for the total column ozone estimation using two different approaches: (i) ozone channel observation along with the a-priori estimate of temperature and water vapour profile and (ii) only sounder channels observations. The accuracy of the retrieval algorithms was examined for different errors in the atmospheric profiles for the method (i) and different sensor noise specification for the method (ii). This study has shown that accurate temperature information is very important for ozone estimation and lower instrument noise results in better ozone estimates.     

Catchment area‐based evaluation of the AMC‐dependent SCS‐CN‐based rainfall–runoff models

Using a large set of rainfall–runoff data from 234 watersheds in the USA, a catchment area‐based evaluation of the modified version of the Mishra and Singh (2002a) model was performed. The model is based on the Soil Conservation Service Curve Number (SCS‐CN) methodology and incorporates the antecedent moisture in computation of direct surface runoff. Comparison with the existing SCS‐CN method showed that the modified version performed better than did the existing one on the data of all seven area‐based groups of watersheds ranging from 0·01 to 310·3 km². Copyright © 2005 John Wiley & Sons, Ltd.     

Seasonal and spatial variations in the scaling and correlation structure of streamflow data

Seasonal and spatial variability in scaling, correlation and wavelet variance parameter of daily streamflow data were investigated using 56 gauging stations from five basins located in two different climate zones. Multifractal temporal scaling properties were detected using a multiplicative cascade model. The wavelet variance parameter yielded persistence properties of the streamflow time series. Seasonal variations were found to be significant in that winter and spring seasons where large‐scale frontal events are dominant showed higher long‐term correlations and less multifractality than did summer and fall seasons. Coherent spatial variations were apparent. The Neches River basin located in a subtropic humid climate zone exhibited high persistence and long‐term correlation as well as less multifractality as compared with other basins. It is found that larger drainage areas tend to have smaller multifractality and higher persistence structure, and this tendency becomes apparent in regions that receive large amounts of precipitation and decreases towards arid regions. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of convective scale downdrafts on the rainfall simulation in NCAR-CAM3

In this work, an attempt is made to systematically evaluate the effect of convective scale downdrafts on the model-simulated rainfall, in both aqua- and actual-planet frameworks, using the NCAR CAM3. From the aqua-planet simulations, it was found that there is a reduction in the total rainfall (TRF) with increase in the intensity of downdrafts, which is primarily attributed to the reduction in the deep convective component (DRF). However, with stronger downdrafts, the shallow convective and the large-scale components (SRF and LRF, respectively) are found to increase. The reduction in DRF is due to the increased evaporation of convective precipitation within the downdrafts. It is found that, with intense downdrafts, there is an increase in relative humidity throughout the troposphere, due to the combined effect of both moisture and temperature. There is an overall increase in specific humidity of the atmosphere with stronger downdrafts, excepting at around the 900-hPa level. In addition, there is a reduction in temperature throughout the troposphere, primarily due to the reduction in the overall temperature tendency due to moist processes and that due to the radiative processes. The changes in the radiative forcing are found to be primarily due to a significant increase in the low cloud fraction with strong downdrafts. In the actual-planet framework, it is seen that, with strong convective downdrafts, there is a reduction in TRF and DRF and a corresponding increase in SRF and LRF, similar to the results obtained from the aqua-planet simulations. The vertical structures of the thermodynamic variables (RH, q, and T) show similar sensitivity to the downdraft intensity as that seen in the aqua-planet framework. Sensitivity of frequency and intensity of model-simulated rainfall to the downdraft intensity was also analyzed, and it was seen that there were significant differences in the frequency distribution of rainfall. It was seen that, with an increase in downdraft intensity, there is an increase in the frequency of light rain (1–10?mm/day) for TRF with a corresponding reduction in all other rainfall bins. A similar behavior was seen for the DRF as well, while the SRF and LRF components showed an increase in rainfall accumulation in all the bins. In addition, the impact of convective downdrafts on the mean spatial pattern of rainfall is also analyzed, for the DJF and JJA periods (boreal winter and summer, respectively). For the DJF period, with strong downdrafts, it was seen that grossly over the whole domain, there were a reduction in DRF and an increase in SRF and LRF. In contrast, during JJA, although a major part of the domain showed a reduction in DRF, there were regions like western Arabian Sea and the Somali coast with increase in DRF with intense downdrafts. The SRF and LRF components, however, show a spatially homogeneous increase over almost the entire domain with increase in downdraft intensity.     

Electrokinetic properties and flotation behaviour of apatite and calcite in the presence of sodium oleate and sodium metasilicate

Calcite is generally associated with apatite minerals in phosphate deposits. To explore the possibility of separating these minerals by a soap flotation technique, their electrokinetic properties and flotation behaviour were studied in the presence of sodium oleate.Microelectrophoresis data indicate oleate adsorption on these minerals, and from Hallimond-tube flotation tests it has been noted that in a controlled pH environment and for a certain sodium oleate concentration range, separation of these minerals is possible.The study of apatite/calcite-sodium metasilicate-sodium oleate systems indicates the preferential adsorption of silicate at the calcite surface. This suggests the potential use of sodium metasilicate as the modifying agent for the separation of apatite from calcite by depressing calcite when using sodium oleate as collector.