Impact of horizontal resolution on prediction of tropical cyclones over Bay of Bengal using a regional weather prediction model

The present study is carried out to examine the performance of a regional atmospheric model in forecasting tropical cyclones over the Bay of Bengal and its sensitivity to horizontal resolution. Two cyclones, which formed over the Bay of Bengal during the years 1995 and 1997, are simulated using a regional weather prediction model with two horizontal resolutions of 165 km and 55 km. The model is found to perform reasonably well towards simulation of the storms. The structure, intensity and track of the cyclones are found to be better simulated by finer resolution of the model as compared to the coarse resolution. Rainfall amount and its distribution are also found to be sensitive to the model horizontal resolution. Other important fields, viz., vertical velocity, horizontal divergence and horizontal moisture flux are also found to be sensitive to model horizontal resolution and are better simulated by the model with finer horizontal grids.     

Chlorine-36 in groundwater of the United States: empirical data

Natural production of the radionuclide chlorine-36 (³⁶Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear weapons, has also produced large amounts of ³⁶Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the probable preanthropogenic levels of ³⁶Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional pattern of ³⁶Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of ³⁶Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States. Electronic Publication     

Fault plane solutions of the january 26th, 2001 bhuj earthquake sequence

A 12-station temporary microearthquake network was established by the Geological Survey of India for aftershock monitoring of the January 26th, 2001 Bhuj earthquake (M _w 7.6) in the Kutch district of Gujarat state, western India. The epicentres of the aftershocks show two major trends: one in the NE direction and the other in the NW direction. Fault-plane solutions of the best-located and selected cluster of events that occurred along the NE trend, at a depth of 15–38 km, show reverse faulting with a large left-lateral strike-slip motion, which are comparable with the main-shock solution. The NW trending upper crustal aftershocks at depth <10 km, on the other hand, show reverse faulting with right-lateral strike-slip motion, and the mid crustal and lower crustal aftershocks, at a depth of 15–38 km, show pure reverse faulting as well as reverse faulting with right-lateral and left-lateral strike-slip motions; these solutions are not comparable with the main-shock solution. It is inferred that the intersection of two faults has been the source area for stress concentration to generate the main shock and the aftershocks.     

Assessment of groundwater vulnerability to pollution in Dire Dawa,Ethiopia using DRASTIC

Assessment of groundwater vulnerability to pollution is an effective tool for the delineation of groundwater protection zones. DRASTIC approach was used to determine vulnerability zones in Dire Dawa groundwater basin, a semiarid region of Ethiopia. Maps of the seven DRASTIC parameters were prepared. GIS-ArcView was used for mapping and performing weighted-overlay analysis. The result of the analysis indicated that eastern part of the study area, in which Dire Dawa town is located, is highly vulnerable. A low aquifer vulnerability class was determined for the western portion of the study area as a result of greater groundwater depths, higher relative soil-clay content, and relatively low recharge rates for this area. The area between the two zones is of medium vulnerability. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. Some of the boreholes in the Sabian well field (Dire Dawa area) already deliver groundwater with nitrate levels significantly exceeding health standards set by the World Health Organization, while boreholes in the western part (low vulnerability zone) contain almost no nitrate. The result of this study is useful for risk assessments and for the development of effective groundwater management strategies for this region and others like it.     

Structural and magnetic fabric studies of recess structures in the western Himalaya: Implications for 1905 Kangra earthquake

Kinematic information from deformation structures and magnetic fabrics are used to infer recent tectonics around Kangra and Dehradun recesses, western Himalaya. Three types of magnetic fabrics (Type I & II, III, and IV) are identified based on the angle between K3 axis and bedding pole. It was observed that Kangra recess shows more mature fabric type IV as compared to Dehradun recess, where orientation of K3 axes and tectonic fabric reveals dominance of superposed deformation. In the vicinity of Dehradun recess, normal faults occur in un-indurated Quaternary fan deposits confirming their recent formation. The observations are in conformity with earlier studies that during the 1905 Kangra earthquake, the Main Boundary Thrust (MBT) (or one of its subsidiary thrusts) near Kangra showed thrusting whereas the MBT near Dehradun underwent either normal faulting or post seismic adjustments characteristic of normal faulting. The thrusting could be a result of subsurface processes whereas the normal faulting was a result of prevailing surface strains.     

The Darasun gold deposit,Eastern Transbaikal region: Chemical composition,REE patterns,and stable carbon and oxygen isotopes of carbonates from ore veins

The chemistry, REE patterns, and carbon and oxygen isotopic compositions of carbonates from ore veins of the Darasun deposit are discussed. In addition to the earlier described siderite, calcite, and carbonates of the dolomite-ankerite series, kutnahorite is identified. The total REE content in Fe-Mg carbonates of the dolomite-ankerite series (2.8–73 ppm) is much lower than in later calcite (18–390 ppm). δ¹³C of Fe-Mg carbonates and calcite varies from +1.1 to −6.7‰ and from −0.9 to −4.9‰, respectively. δ¹⁸O of Fe-Mg carbonates and calcite varies from +17.6 to 3.6‰ and from +15.7 to −0.5‰, respectively. The REE sum and carbon and oxygen isotopic compositions reveal zonal distribution relative to the central granodiorite porphyry stock. The correlation between the carbon and oxygen isotopic compositions and REE sum reflects variations in the physicochemical formation conditions and composition of ore-forming fluid. The isotopic composition of fluid is calculated, and possible sources of its components are considered. Earlier established evidence for a magmatic source of ore-forming fluid and participation of meteoric water in ore formation is confirmed. Geochemical evidence for interaction of ore-forming fluid with host rocks is furnished. The relationships between the REE sum, on the one hand, and carbon and oxygen isotopic compositions of hydrothermal ore-forming fluid, on the other, are established.     

Petrology and geochemistry of greywackes from Goa-Dharwar sector,western Dharwar Craton: Implications for volcanoclastic origin

Late Archaean Supracrustals of the Goa-Dharwar sector (GDS) are composed of a thick sequence of greywacke sequence with narrow intercalations of quartzite, BIF and carbonates. Mafic volcanics occupy the base of the sequence. The greywackes are predominantly tuffacious containing chlorite-sericite and hornblende. Arkosic variations containing biotite dominate the western part of the sector. Fine-grained variations occur as isolated narrow lenses within other types of greywackes. The conglomeratic greywackes are localized along the western and the eastern margins of the sector. All of the greywackes are all typically immature containing coarser clasts of mostly plagioclase (18–23%) and quartz (32–34%). Lithic fragments of felsic volcanic rocks are common. The matrix is dominated by mafic material. Biotite and amphibole are related to metamorphic recrystallization. Chlorite, sericite, epidote, carbonate and chert are products of the interplay of diagenesis and low-grade metamorphism. Fe-Ti oxide, sphene, apatite and zircon are usual accessories. But for slight enrichment in K₂O, the major element chemistry of the GDS greywackes is similar to the chemistry of Late Archaean greywackes. They also compare in respect of V, Co, Hf contents, K₂O/Na₂O, SiO₂/Al₂O₃, Na₂O/Al₂O₃, Ba/Rb, Th/U, La/Th, Sm/Nd ratios, steep REE patterns with distinct LREE enrichment and HREE depletion. The GDS greywackes however are distinctly enriched in Rb, Ba, Sr, Th, U, Cu, Zr, Ce/Ce* and depleted in Cr, Ni, and Zn. The conglomeritic and biotite bearing verities contain considerable proportions of clasts derived from the basement tonalitic/granitic terrain. The common tuffacious greywackes containing hornblende and biotite-sericite however include only volcanic clasts and bear evidence of derivation from submarine weathering of predominantly felsic volcanics erupted on a large scale to form a magmatic arc in the later stages of geosynclinal deposition. Geochemical data suggest that the GDS greywackes were laid down in progressively changing basin geometry from a passive to active continental margin and island arc setting.     

Permian fusulinids of the East Hindu Kush and West Karakorum (Pakistan)

Fusulinids from the Rosh Gol, Mastuj, Reshun Gol (East Hindu Kush) and Baroghil (West Karakorum) localities are studied. Five successive fusulinid assemblages from the Rosh Gol section characterize the Sakmarian (?), Yakhtashian-Bolorian, and Kubergandian stages of the Permian. Fusulinids of the Sakmarian (?) Stage are discovered in the Baroghil locality. In the Mastuj and Reshun Gol localities, rocks of natural outcrops, talus cones, and pebbles of the Cretaceous conglomerates yield predominantly the Kubergandian fusulinids accompanied sometimes by the Sakmarian (?) and Bolorian forms. Four new species Monodiexodina talenti, Nonpseudofusulina conaghani, N. yarkhunensis, and N. mawsoni are described.     

Geochemistry of core sediments from Mullipallam creek,South East coast of India

The Mullipallam creek in Muthupet mangroves region is the only E-W trending coastal strip in the SE coast of India and is very important, as the mangrove acts as a barrier to natural diasters. Natural, anthropogenic signals and accumulation of elements were made by collecting sediment samples at various depths in a core. All sediments were analyzed for carbonates (CaCO₃), organic carbon (OC), major (Si, Al, Fe, Na, K, Ca, Mg, P), and trace (Mn, Cr, Cu, Ni, Co, Pb, Zn). Normalization with Al values has been done for all the major and trace elements and enrichment factors have been calculated. The calculated enrichment factors and comparison indicate that the trace metals (especially Pb) are enriched mainly due to the external (anthropogenic) activities in the land as well as in the coastal zone (Palk Strait).