Diagnosis of satellite-derived outgoing long wave radiation in relation to rainfall in India

Summary The implications of the hydrostatic assumption for an anelastic two-dimensional numerical model of a gravity current intruding into a neutrally stratified environment are studied. Particular interest is focused on situations where the gravity current encounters an orographic barrier. Considerable discrepancies between hydrostatic and nonhydrostatic calculations are found in the head region for high Froude numbers, when the resolution is high enough to resolve the head of the current. However, the propagation speed and the depth of the feeder flow are well represented in the hydrostatic model.With 15 Figures     

Soil Carbon Sequestration in India

With a large land area and diverse ecoregions, there is a considerable potential of terrestrial/soil carbon sequestration in India. Of the total land area of 329 million hectares (Mha), 297 Mha is the land area comprising 162 Mha of arable land, 69 Mha of forest and woodland, 11 Mha of permanent pasture, 8 Mha of permanent crops and 58 Mha is other land uses. Thesoil organic carbon (SOC) pool is estimated at 21 Pg (petagram = Pg = 1 ×10¹⁵ g= billion ton) to 30-cm depth and 63 Pg to 150-cm depth. The soil inorganic carbon (SIC) pool is estimated at 196 Pg to 1-m depth. The SOC concentration in most cultivated soils is less than 5 g/kg compared with 15 to 20 g/kg in uncultivated soils. Low SOC concentration is attributed to plowing, removal of crop residue and other biosolids, and mining of soil fertility. Accelerated soil erosion by water leads to emission of 6 Tg C/y. Important strategies of soil C sequestration include restoration of degraded soils, and adoption of recommended management practices (RMPs) of agricultural and forestry soils. Potential of soil C sequestration in India is estimated at 7 to 10 Tg C/y for restoration of degraded soils and ecosystems, 5 to 7 Tg C/y for erosion control, 6 to 7 Tg C/y for adoption of RMPs on agricultural soils, and 22 to 26 Tg C/y for secondary carbonates. Thus, total potential of soil C sequestration is 39 to 49 (44± 5) Tg C/y.     

Characteristics of fission tracks in zircon: Applications to Geochronology and Cosmology

We describe a simple method for nearly isotropic revelation of fission tracks in zircon. The etchant is an equivolume mixture of 48% HF and 98% H₂SO₄; etching is carried out under pressure at 150° – 180°C. For fossil track densities above ～ 5 × 10⁶, the etching time is strongly anticorrelated with track density. The total etchable fission fragment track length (2 fragments) is 11 ± 0.5 μm. The length distribution is sharply peaked; the standard deviation in different samples is ± (0.7 – 0.8) μm. Thermal annealing studies indicate a lower activation energy for track fading than was previously repoted using a phosphoric acid etchant. A practical chemical dissolution method is described for quantitatively recovering zircon crystals from rock samples; this method should find application in fission track dating of even zircon poor rocks.     

Characteristics of aerosol optical depth and Ångström parameters over Mohal in the Kullu Valley of Northwest Himalayan Region,India

The measurements using a ground based multi wavelength radiometer (MWR) at Mohal (31°54′N, 77°07′E, 1154 m AMSL) in the Kullu valley of Northwestern Himalayan region show that the spectral aerosol optical depth (AOD) and turbidity coefficient, β, are high in summer, moderate in monsoon season, low in winter and lowest in autumn, while wavelength exponent, α, has an opposite trend. Average annual value of AOD at 500 nm is 0.24±0.01, 0.43±0.02, and 0.28±0.02; that of β is 0.14±0.01, 0.22±0.02, and 0.17±0.03; and that of α is 1.06±0.09, 1.16±0.10, and 0.86±0.13, respectively, for clear, hazy and partially clear sky days. The considerably greater value of β on hazy days indicates more coarse particles in mountain haze. The fractional asymmetry factor (AF) is more negative in summer and autumn months. The AOD and β have significantly positive correlation with temperature and wind speed, suggesting high AODs and turbidity on hot and windy days.     

Holocene Sea Levels and Coastal Change,South-west Viti Levu Island,Fiji

For the first time, a sediment core spanning the entire Holocene has been analysed from Fiji. The 6 m core was obtained from the floor of an ancient coastal lagoon (palaeolagoon) adjacent to Bourewa, the site of the earliest known human settlement in this island group. The basal sediments, just above bedrock, date from 11 470 cal bp. A major transition occurs around 8000 cal bp where marine influences on palaeolagoon sedimentation increase sharply. Full shallow-water marine conditions are attained around 4630 cal bp and last until 3480 cal bp after which there is a regressive phase. The results agree with the area-specific predictions of sea level in the ICE-4G model, particularly in the timing of the highstand. In addition, the results support the ideas (a) that early human colonisation of Fiji occurred during the late Holocene regression, (b) that the first inhabitants of Bourewa utilised both nearshore marine (reefal) and brackish lagoon food sources, and (c) that the abrupt human abandonment of the area around 2500 cal bp could have been prompted by a reduction in these resources driven largely by sea-level fall.     

Paleo-uplift and cooling rates from various orogenic belts of India, as revealed by radiometric ages

The significant discordance of the radiometric (Rb-Sr, Pb-U, K-Ar and fission track) ages from various orogenic cycles of the Dharwar, Satpura, Aravalli and Himalayan orogenic belts in India, coupled with their corresponding blocking temperatures for various radiometric clocks in whole rocks and minerals, has been used to evaluate the cooling and the uplift histories of the respective orogenic belts. The blocking temperatures used in the present study of various Rb-Sr (isotopic homogenization at 600°C, muscovite at 500°C and biotite at 300°C), Pb-U (monazite at 530°C), K-Ar (muscovite at 350°C and biotite at 300°C) and fission-track clock (zircon at 350°C, sphene at 300°C, garnet at 280°C, muscovite at 130°C, hornblende at 120°C and apatite at 100°C for the cooling rate l°C/Ma) have been found suitable to explain the differences in mineral ages by different radiometric techniques. The nature of the cooling curves drawn using the temperature versus age data for various orogenic cycles in India has also been discussed. The cooling and the uplift patterns determined for various orogenic cycles of India, suggest comparatively slow cooling (5.0–0.2°C/Ma) and uplift (180–2 m/Ma) for the Peninsular regions and rapid cooling (25.0–1.0° C/Ma) and fast uplift (800–30 m/Ma) during the Himalayan Orogenic Cycle (Upper Cretaceous—Tertiary) in the Extra-Peninsular region.     

Equilibrium structure of differentially rotating polytropic models of the stars

In this paper we propose a method for computing the equilibrium structure of differentially rotating polytropic models of the stars. A general law of differential rotation of the type ²=b ₀+b ₁ s ²+b ₂ s ⁴, which can account for a reasonably large variety of possible differential rotations in the stars has been used. The distortional effects have been incorporated in the structure equations up to second order of smallness in distortion parametersb ₀,b ₁, andb ₂ using Kippenhahn and Thomas' averaging approach in conjunction with Kopal's results on Roche equipotentials in manner similar to the one earlier used by Mohan and Saxena for computing the equilibrium structure of polytropes having solid body rotation. Numerical results have been obtained for various types of differentially rotating polytropic models of stars of polytropic indices 1.5, 3, and 4. Certain differentially rotating models of the Sun which are possible with such a type of law of differential rotation, have also been computed.     

Water Resources of the South Asian Region in a Warmer Atmosphere

The global mean surface temperature may rise by about 0.3oC per decade during the next Few decades as a result of anthropogenic greenhouse gas emissions in the earth’s atmosphere. The data generated in the greenhouse warming simulations (Business-as-Usual scenario of IPCC) with the climate models developed at Max Planck Institute for Meteorology, Hamburg have been used to assess future plausible hydrological scenario for the South Asian region. The model results indicate enhanced surface warming (2.7oC for summer and 3.6oC for winter) over the land regions of South Asia during the next hundred years. While there is no significant change in the precipitation over most of the land regions during winter, substantial increase in precipitation is likely to occur during summer. As a result, an increase in soil moisture is likely over central India, Bangladesh and South China during summer but a statistically sig-nificant decline in soil moisture is expected over central China in winter. A moderate decrease in surface runoff may occur over large areas of central China during winter while the flood prone areas of NE-India. Bangladesh and South China are likely to have an increase in surface runoff during summer by the end of next century.