Home About us Contact
|
Home About us Contact | ||
|
|
||
Coherent Pattern (coherent + pattern)
Selected AbstractsThe influence of environment and spawning distribution on the survival of anchovy (Engraulis encrasicolus) larvae in the Bay of Biscay (NE Atlantic) investigated by biophysical simulationsFISHERIES OCEANOGRAPHY, Issue 6 2007GWENHAEL ALLAIN Abstract A growth and survival model of the early life stages was run along virtual drift trajectories tracked in a hydrodynamic model to simulate the annual recruitment process of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). These biophysical simulations concerning three different years were analysed in order to investigate the influence of environment and spawning dynamics on the survival of larvae and juveniles. The location of space,time survival windows suggested major environmental mechanisms involved in simulated recruitment variability at the different scales , retention of larvae and juveniles in favourable habitats over the shelf margins and turbulence effects. These small-scale and meso-scale mechanisms were related to the variations in wind direction and intensity during spring and summer. Survival was also variable according to the origin of the drift trajectories, that is spawning distribution in space and time. The observed spawning distribution (according to field surveys) was compared with the spawning distribution that would maximize survival (according to the biophysical model) on a seasonal scale, which revealed factors not considered in the biophysical model (e.g. spawning behaviour of the different age classes). The variation of simulated survival according to spawning distribution was examined on a multi-annual scale and showed a coherent pattern with past and present stock structures. The interaction processes between the population (influence on spawning) and its environment (influence on survival) and its implications on recruitment and stock dynamics are discussed. [source] Effect of autumn and winter meteorological variables on spring aphid populations in the Po valley, Northern ItalyJOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2001D. Rongai Prediction of aphid populations is crucial to the successful application of control strategies. In previous studies clear relationships between aphid catches and meteorological variables were highlighted. The primary objective of this study was to quantify the effects of autumn and winter meteorological variables on the aphid species populations the following spring. The data on all the species caught at two Italian sites (Ozzano Emilia and Budrio) up to 31 May from 1992 to 1999 were used for this study. Different models were found according to the aphid biological cycle (i.e. holocycle, anholocycle, holo-anholocycle). A fourth group of minor species, designated as ,others', was properly modelled as holo-anholocycle species. A satisfactory fit was observed when holocycle species were plotted against minimum temperature and precipitation in October, anholocycle species against minimum temperature and precipitation in December,January, holo-anholocycle species and ,others' against wind speed and number of frosty days in November, and minimum temperature and precipitation in December,January. Model response was more consistent at Budrio (open flat site) than at Ozzano Emilia (flat site delimited by a hill). A coherent pattern was found with an overall comparison of the estimates against observations. The possibility offered by these empirical models for forecasting spring aphid populations of all species at a given site is clearly of interest. This first study encouraged further investigation aimed at validating models before applying them in practice. [source] Variation in peak P,T conditions across the upper contact of the UHP terrane, Dabieshan, China: gradational or abrupt?JOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2006Y. SHI Abstract The Southern Dabieshan Terrane (SDT) has previously been divided into high-pressure (HP) and ultrahigh-pressure (UHP) terranes, and its regional extent and the tectonic nature of its boundaries are hotly debated topics. In this study, an eclogite-bearing area of 100 km2 near Taihu is mapped in detail, and divided into Northern, Middle and Southern Zones on the basis of lithological characteristics. The Northern Zone consists of epidote-biotite gneiss and eclogite blocks, the Middle Zone includes granitic gneiss, biotite gneiss, eclogites and amphibolite, and the Southern Zone is composed mainly of garnet-bearing mica schist. The eclogites occur mainly as lens or blocks in the Northern and Middle Zones. The peak P,T conditions for 61 eclogite samples across the area are estimated using the Grt-Cpx Fe2+ -Mg thermometers and the Grt-Cpx-Phe barometers. The results indicate three different P,T regions: 2.82,4.09 GPa/759,942 °C in the Northern Zone, and 2.00,3.54 GPa/641,839 °C in the granitic gneiss and 1.38,2.36 GPa/535,768 °C in the biotite gneiss from the Middle Zone. Combined with the spatial distribution of eclogites across the area, the P,T values for eclogites increase continuously from the south to the north, defining a reference ,geotherm' of 5 °C km,1. However, some unreasonable apparent gradients can be established along two south,north profiles across the area, and display a P,T difference between the Northern and Middle zones. On the basis of the average P,T data for eclogites across the area, a gap of at least 0.3 GPa/20 °C exists between the Northern and Middle zones. By contrast, the P,T values of eclogites from the Middle zone show a coherent pattern with transitional characteristics from HP in the south to UHP in the north. We suggest that the SDT was a coherent slab during subduction, and was broken up by a major fault during exhumation, which was formed under UHP metamorphic conditions. [source] Measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravelEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2004Colin D. Rennie Abstract Maps are presented of the spatial distribution of two-dimensional bedload transport velocity vectors. Bedload velocity data were collected using the bottom tracking feature of an acoustic Doppler current pro,ler (aDcp) in both a gravel-bed reach and a sand-bed reach of Fraser River, British Columbia. Block-averaged bedload velocity vectors, and bedload velocity vectors interpolated onto a uniform grid, revealed coherent patterns in the bedload velocity distribution. Concurrent Helley-Smith bedload sampling in the sand-bed reach corroborated the trends observed in the bedload velocity map. Contemporaneous 2D vector maps of near-bed water velocity (velocity in bins centered between 25 cm and 50 cm from the bottom) and depth-averaged water velocity were also generated from the aDcp data. Using a vector correlation coef,cient, which is independent of the choice of coordinate system, the bedload velocity distribution was signi,cantly correlated to the near-bed and depth-averaged water velocity distributions. The bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress. Published in 2004 by John Wiley & Sons, Ltd. [source] Spatial patterns of water surface topography at a river confluenceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2002Dr Pascale M. Biron Abstract Understanding flow structures in river confluences has largely been the product of interpretations made from measured flow velocity data. Here, we turn the attention to the investigation of the patterns of both the average and standard deviations of the micro-topography of the water surface at an asymmetrical natural discordant confluence for different flow conditions. Water surface topography is measured using a total station to survey the position of a reflector mounted on a custom-built raft. To limit error problems related to changes in the water level, measurements are taken and analysed by cross-stream transects where five water surface profiles are taken before moving to the next transect. Three-dimensional numerical simulations of the flow dynamics at the field site are used to examine predicted water surface topography for a steady-state situation. The patterns are interpreted with respect to flow structure dynamics, visual observations of boils, and bed topography. Results indicate that coherent patterns emerge at the water surface of a discordant bed confluence for different flow conditions. The zone of stagnation and the mixing layer are characterized by super-elevation, a lateral tilt is present at the edge of the mixing layer, and a zone of super-elevation is present on the tributary side at the downstream junction corner. The latter seems associated with periodical upwelling and is not present in the numerical simulations that do not take into account instantaneous velocity fluctuations. Planform curvature, topographic steering related to the tributary mouth bar, and turbulent structures associated with the mixing layer all play a key role in the pattern of both the average and standard deviation of the water surface topography at confluences. Copyright © 2002 John Wiley & Sons, Ltd. [source] Recent variations in seasonality of temperature and precipitation in Canada, 1976,95INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2002Paul H. Whitfield Abstract A previously reported analysis of rehabilitated monthly temperature and precipitation time series for several hundred stations across Canada showed generally spatially coherent patterns of variation between two decades (1976,85 and 1986,95). The present work expands that analysis to finer time scales and a greater number of stations. We demonstrate how the finer temporal resolution, at 5 day or 11 day intervals, increases the separation between clusters of recent variations in seasonal patterns of temperature and precipitation. We also expand the analysis by increasing the number of stations from only rehabilitated monthly data sets to rehabilitated daily sets, then to approximately 1500 daily observation stations. This increases the spatial density of data and allows a finer spatial resolution of patterns between the two decades. We also examine the success of clustering partial records, i.e. sites where the data record is incomplete. The intent of this study was to be consistent with previous work and explore how greater temporal and spatial detail in the climate data affects the resolution of patterns of recent climate variations. The variations we report for temperature and precipitation are taking place at different temporal and spatial scales. Further, the spatial patterns are much broader than local climate regions and ecozones, indicating that the differences observed may be the result of variations in atmospheric circulation. Copyright © 2002 Environment Canada. Published by John Wiley & Sons, Ltd. [source] | ||||||||||