Signature of a southern hemisphere extratropical influence on the summer monsoon over India

The weakening relationship of El Nino with Indian summer monsoon reported in recent years is a major issue to be addressed. The altered relationships of Indian monsoon with various parameters excite to search for other dominant modes of variability that can influence the precipitation pattern. Since the Indian summer monsoon circulation originates in the oceanic region of the southern hemisphere, the present study investigates the association of southern extratropical influence on Indian summer monsoon using rainfall and reanalysis parameters. The effect of Southern Annular Mode (SAM) index during the month of June associated with the onset phase of Indian summer monsoon and that during July–August linked with the active phase of the monsoon were analysed separately for a period from 1951 to 2008. The extra-tropical influence over the monsoon is illustrated by using rainfall, specific humidity, vertical velocity, circulation and moisture transport. The June high SAM index enhances the lower level wind flow during the onset phase of monsoon over Indian sub-continent. The area of significant positive correlation between precipitation and SAM in June also shows enhancement in both ascending motion and specific humidity during the strong phase of June SAM. On the other hand, the June high SAM index adversely affects July–August monsoon over Indian subcontinent. The lower level wind flow weakens due to the high SAM. Enhancement of divergence and reduction in moisture transport results in the Indian monsoon region due to the activity of this high southern annular mode. The effect is more pronounced over the southwest region where the precipitation spell has high activity during the period. Significant correlation exists between SAM and ISMR, even after removing the effect of El Nino. It indicates that the signals of Indian summer monsoon characteristics can be envisaged to a certain extend using the June SAM index.     

Constraining basin thermal history and petroleum generation using palaeoclimate data in the Piceance Basin,Colorado

Careful assessment of basin thermal history is critical to modelling petroleum generation in sedimentary basins. In this paper, we propose a novel approach to constraining basin thermal history using palaeoclimate temperature reconstructions and study its impact on estimating source rock maturation and hydrocarbon generation in a terrestrial sedimentary basin. We compile mean annual temperature (MAT) estimates from macroflora assemblage data to capture past surface temperature variation for the Piceance Basin, a high‐elevation, intermontane, sedimentary basin in Colorado, USA. We use macroflora assemblage data to constrain the temporal evolution of the upper thermal boundary condition and to capture the temperature change with basin uplift. We compare these results with the case where the upper thermal boundary condition is based solely upon a simplified latitudinal temperature estimate with no elevation effect. For illustrative purposes, 2 one‐dimensional (1‐D) basin models are constructed using these two different upper thermal boundary condition scenarios and additional geological and geochemical input data in order to investigate the impact of the upper thermal boundary condition on petroleum source rock maturation and kerogen transformation processes. The basin model predictions indicate that the source rock maturation is very sensitive to the upper thermal boundary condition for terrestrial basins with variable elevation histories. The models show substantial differences in source rock maturation histories and kerogen transformation ratio over geologic time. Vitrinite reflectance decreases by 0.21%Ro, source rock transformation ratio decreases 10.5% and hydrocarbon mass generation decreases by 16% using the macroflora assemblage data. In addition, we find that by using the macroflora assemblage data, the modelled depth profiles of vitrinite reflectance better matches present‐day measurements. These differences demonstrate the importance of constraining thermal boundary conditions, which can be addressed by palaeotemperature reconstructions from palaeoclimate and palaeo‐elevation data for many terrestrial basins. Although the palaeotemperature reconstruction compiled for this study is region specific, the approach presented here is generally applicable for other terrestrial basin settings, particularly basins which have undergone substantial subaerial elevation change over time.     

Progress towards better weather forecasts for city dwellers: from short range to climate change

Summary The current resolution of operational weather forecast model is not sufficient in general to explicitly resolve even the major cities of the World. As a consequence, urban areas have traditionally been neglected in such models. The introduction of tiled land surface models has enabled sub-gridscale landuse to be modelled, and hence has provided the opportunity to model cities within weather forecast models. However, to date there has been little effort made within the operational weather forecast community. At present there is only one operational centre that explicitly resolves urban areas. This centre includes a simple urban scheme within its mesoscale and global models, which has been shown to have a positive impact on the forecast. However, with the recent developments within urban meteorology there are now a variety of urban schemes, which vary in their complexity and parameter requirements, that would be suitable for operational weather forecast models. So it is likely that more operational models, and in particular mesoscale models, will include urban areas in the near future. With the majority of the World‘s population living in cities, the resilience of these cities to the impacts of climate change is also becoming of increasing interest. This means that urban areas will have to be included within climate change simulations, as well as weather forecast simulations, in the future. At present, only one climate change model has included a parametrisation for urban areas. However, this is likely to increase if work in this area grows rapidly.     

Seismic hazard assessment using intensity point data

The influence of the attenuation model used in seismic hazard assessment in terms of intensity and acceleration is studied. For two sites in central Italy, the catalogue of the actual observed intensities during the last three centuries has been recovered. In the study region, the data collected during a recent seismic sequence give the basis for relating intensity and acceleration. The results show the importance of establishing statistical relationships among the used quantities, based on a representative set of data.     

加拿大不列颠哥伦比亚省温哥华岛纳奈莫群的帆翼龙类化石

An unusual jaw found in a calcite nodule from Collishaw Point, Hornby Island, British Columbia (off the east coast of Vancouver Island) represents the first definitive pterosaur found in British Columbia, and the first istiodactylid from Canada.     

Assessment of boundary-element method for modelling a free-floating sloped wave energy device. Part 1: Numerical modelling

The boundary-element method has been widely used as a design tool in the offshore and ship building industry for more than 30 years. Its application to wave energy conversion is, however, more recent. This paper deals with the numerical modelling of a free-floating sloped wave energy device. The power take-off mechanism of the device consists of an immersed tube with a piston sliding inside. The modelling is done using the boundary-element method package WAMIT. The model is first worked out for the case where the axis of the tube is vertical. It is then derived for the tube inclined and successfully verified against numerical benchmark data. A companion paper presents results of a detailed comparison with a physical model study.     

Petrogenetic evolution of the Koziakas ophiolite complex (W. Thessaly, Greece)

Summary The Koziakas ophiolitic complex is situated in W. Thessaly and is interpreted as an incomplete ophiolite sequence, thrust over the Western Thessaly Unit (W.T.U.). Two tectonically distinct units represent it: (1) the lower unit with a metamorphic sole and a tectonosedimentary mélange and (2) the upper unit including mantle peridotites and basaltic lavas. The mantle peridotites are composed by harzburgite, lherzolite and plagioclase lherzolite intruded by a sparse network of gabbroic, plagiogranitic and doleritic dykes. The volcanic sequence of the upper unit can be geochemically subdivided into four groups of basalts with: (1) tholeiitic N-type MORB affinities, (2) low-Ti boninitic affinities, (3) subalkalic E-MORB type affinities and (4) alkali characteristics displaying a different petrogenetic evolution with respect to the other groups. The magmatic history of the Koziakas ophiolite is in agreement with extensive fractional crystallization and variable degrees of partial melting of a heterogeneous mantle source, yielding, magmas mainly of MORB composition. Modal and cryptic metasomatic phenomena of the mantle peridotites as well as Sr-Nd isotopic ratios imply that this melt contained also a hydrous component derived from melting of a subducted lithosphere. The above geochemical characteristics and the correlation with the adjacent ophiolite suites of Pindos, Othris and Vourinos indicate that Koziakas ophiolitic complex formed in a small backarc basin situated at the eastern margin of the greater Pindos Ocean, between the Western Thessaly Unit (W.T.U.) and the Pelagonian continent.     

The geological history and geodynamics of the Earth

The Earth formed through a hot accretion process. Almost simultaneously, the core and the mantle were separated from each other. At the final stages of the accretion process, the outer layer approximately 2000 km thick was molten, thus representing a magma ocean. This magma ocean produced the primary crust of the Earth. Surface waters were precipitated from the atmosphere and released from the crystallizing magma ocean. The plate tectonic processes started at around 4.3 to 4 Ga BP. In the Archean, the overall tectonic mechanism was quite specific, due to substantially higher mantle temperature and thicker oceanic crust. The normal plate tectonics acted during the Proterozoic and Phanerozoic with the periodic assembly of continents, which are known as supercontinent cycles.     

Geochemistry and Petrogenesis of Siwana Peralkaline Granites, West of Barmer, Rajasthan, India

The bimodal Malani suite, West of Barmer, Rajasthan is characterized by discontinuous, ring shaped outcrops of Siwana peralkaline granite with minor outcrops of basalt. The peralkaline, within- plate and A-type nature of granite are evident by its chemical characteristics. The granite is characterized by high Na₂O+K₂O, Fe/Mg, Zr, Nb, Y, Zn; low Al₂O₃, CaO and Sr and is significantly low in absolute abundance of trace and REE elements compared to type area Siwana granite. The granite is correlated to the “Pan-African” event and its petrogenesis and tectonic significance are discussed.     

Comparison of garnet-biotite, calcite-graphite, and calcite-dolomite thermometry in the Grenville Orogen; Ontario, Canada

The Elzevir Terrane of the Grenville Orogen in southern Ontario contains metapelites and abundant graphitic marbles that were regionally metamorphosed from the upper greenschist to upper amphibolite facies. Comparative thermometry was undertaken with widely used calibrations for the systems garnet-biotite, calcite-dolomite, and calcite-graphite. Temperatures that are obtained from matrix biotites paired with prograde garnet near-rim analyses are usually consistent with those determined using calcite-graphite thermometry. However, calcite-graphite thermometry occasionally yields low temperatures due to lack of equilibration of anomalously light graphite. Application of calcite-graphite and garnet-biotite systems may yield temperatures up to 70 °C higher than calcite-dolomite in amphibolite facies rocks. Calcite-dolomite temperatures most closely approach those from calcite-graphite and garnet-biotite when the samples contain a single generation of dolomite and calcite grains contain no visible dolomite exsolution lamellae. However, some of these samples yield temperatures considerably lower than temperatures calculated from calcite-graphite and garnet-biotite thermometry, indicating that the calcite-dolomite thermometer may have been partially reset during retrogression. Estimated peak metamorphic temperatures of regional metamorphism between Madoc (upper greenschist facies) and Bancroft (upper amphibolite facies) range from 500 to 650 °C. These results place the chlorite-staurolite isograd at 540 °C, the kyanite-sillimanite isograd at 590 °C, and the sillimanite-K-feldspar isograd at 650 °C. Although each thermometer may have an absolute uncertainty of as much as ±50 °C, the 50 to 60 °C temperature differences between the isograds are probably accurate to 10 to 20 °C. An incomplete picture of the thermal gradients can result from the application of only one thermometer in a given area. Simultaneous application of several systems allows one to recognize and overcome the inherent limitations of each thermometer. Received: 26 March 1997 / Accepted: 15 April 1998