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.     

Heat flow and crustal thermal structure in the Late Archaean Closepet Granite batholith,south India

The Late Archaean Closepet Granite batholith in south India is exposed at different crustal levels grading from greenschist facies in the north through amphibolite and granulite facies in the south along a ∼400 km long segment in the Dharwar craton. Two areas, Pavagada and Magadi, located in the Main Mass of the batholith, best represent the granitoid of the greenschist and amphibolite facies crustal levels respectively. Heat flow estimates of 38 mW m⁻² from Pavagada and 25 mW m⁻² from Magadi have been obtained through measurements in deep (430 and 445 m) and carefully sited boreholes. Measurements made in four boreholes of opportunity in Pavagada area yield a mean heat flow of 39 ± 4 (s.d.) mW m⁻², which is in good agreement with the estimate from deep borehole. The study, therefore, demonstrates a clear-cut heat flow variation concomitant with the crustal levels exposed in the two areas. The mean heat production estimates for the greenschist facies and amphibolite facies layers constituting the Main Mass of the batholith are 2.9 and 1.8 μW m⁻³, respectively. The enhanced heat flow in the Pavagada area is consistent with the occurrence of a radioelement-enriched 2-km-thick greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented in the Magadi area. The crustal heat production models indicate similar mantle heat flow estimates in the range 12–14 mW m⁻², consistent with the other parts of the greenstone-granite-gneiss terrain of the Dharwar craton.     

Geochemistry of granitoids of Bilgi area,northern part of eastern Dharwar craton,southern India — Example of transitional TTGs derived from depleted source

Mildly deformed granitoids exposed around Bilgi in the northernmost part of the eastern Dharwar craton are divided into two groups viz. granodiorites and monzogranites. The granodiorites contain microgranular enclaves and amphibolite xenoliths, and show low-Al TTG affinity with high SiO₂ (71–74 %), Na₂O, Y and Sr/Y, moderate to moderately high Mg#, Cr and Ni, low to moderate LILE, and low Nb and Ta. However, compared to similar TTGs from different cratons the Bilgi granodiorites have distinctly higher K₂O, K₂O/Na₂O, Rb and lower REE and Th. The amphibolite xenoliths are characterized by variable enrichment of K₂O, Rb, Ba and Th and depletion of Ti, Zr and P compared to MORB. The microgranular enclaves are quartz diorite to granodiorite in composition with high Mg, Ni and Cr, and compared to MORB, are enriched in LILE and depleted in Ti and Y. The monzogranites, compared to the granodiorites, display higher SiO₂, K₂O and Rb with lower Mg#, although still maintaining the high Na₂O, Ni and Cr and low REE character. The Bilgi granodiorites are explained as transitional TTGs late synkinematic with respect to regional deformation. Geochemical signatures and regional geological set up suggest that they are probably derived from partial melting of a highly depleted slab material (metabasalt) followed by variable contamination or assimilation of intermediate crustal rocks in a subduction zone set up. Late stage fluid activity on the granodioritic magma is probably responsible for the generation of monzogranites. The amphibolite xenoliths predate the granodiorites and possibly represent fragments of a schist belt carried away by the granitic magma. They are probably island arc basalt derived from mantle source that has been metasomatized by slab-derived fluids. The microgranular enclaves are coeval with the Bilgi granodiorites and also likely to be island arc magmas derived from mantle variably enriched in slab-derived and within-plate components.     

BED SHEAR IN EVOLVING SCOUR AT A CYLINDER:A THEORETICAL APPROACH

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VORTEX FLOW FIELD IN A SCOUR HOLE AROUND ABUTMENTS

The three-dimensional flow field in a scour hole around different abutments under a clear water regime was experimentally measured in a laboratory flume, using the Acoustic Doppler Velocimeter (ADV). Three types of abutments used in the experiments were vertical-wall (rectangular section), 45° wing-wall (45° polygonal section) and semicircular. The three-dimensional time-averaged velocity components were detected at different vertical planes for vertical-wall abutment and azimuthal planes for wing-wall and semicircular abutments. The velocity components were also measured at different horizontal planes. In the upstream, presentations of flow field through vector plots at vertical / azimuthal and horizontal planes show the existence of a primary vortex associated with the downflow inside the scour hole. On the other hand, in the downstream, the flow field shows a reversed flow near the abutments having a subsequent recovery with a passage of flow as a part of the main flow. The data presented in this p     

FLOW FIELD IN SCOURED ZONE OF CHANNEL CONTRACTIONS

Experiments were conducted in a laboratory flume to measure the two-dimensional turbulent flow field in the scoured zone of channel contractions under a clear-water scour condition. The Acoustic Doppler Velocimeter (ADV) was used to detect the flow field at different vertical lines along the centerline of uncontracted (main channel) and contracted zones of the channel. The distributions of time-averaged velocity components, turbulent intensity, turbulent kinetic energy, and Reynolds stresses are presented in nondimensional graphical form. The bed shear stresses are computed from the measured Reynolds stresses being in threshold condition within the zone of contraction where bed was scoured. The data presented in this paper would be useful to the investigators for the development of kinematic flow model and morphological model of scour at a channel or river contraction.