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Circulation Patterns (circulation + pattern)
Kinds of Circulation Patterns Selected AbstractsMeasurement of Solid Circulation Patterns in Liquid,Solid and Gas,Liquid,Solid Fluidized BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Shahzad Barghi Abstract Solid circulation patterns were determined by measuring collisions between tracer particles and cylindrical probes in liquid,solid and gas,liquid,solid fluidized beds. Special probes were used to obtain two- and three-dimensional views of particle motion. Circulation patterns for 3 and 5 mm glass beads were studied. Mixing cells, which had been formed at low liquid velocities, grew in size and eventually merged as the liquid velocity increased. The flow patterns of smaller particles having the same density as bed particles and particles lighter than bed particles (graphite particles) with the same size were also measured. On a déterminé des profils de circulation des solides en mesurant les collisions entre des traceurs particulaires et des sondes cylindriques dans des lits fluidisés liquide, solide et gaz,liquide,solide. Des sondes spéciales ont été employées pour obtenir des images bidimensionnelle et tridimensionnelle du déplacement des particules. Les profils de circulation pour des billes de verre de 3 mm et 5 mm ont été étudiés. Les cellules de mélange, qui se forment à de faibles vitesses de liquide, augmentent en taille et finissent par fusionner à mesure que la vitesse du liquide augmente. On a également mesuré les profils d'écoulement des particules plus petites ayant la même masse volumique que les particules de lit et des particules plus légères que les particules de lit (particules de graphite) ayant la même taille. [source] Recent advances in understanding the circulation and hydrography of the East China SeaFISHERIES OCEANOGRAPHY, Issue 6 2002Heung-Jae Lie Abstract The physical oceanography of the East China Sea (ECS) has been studied extensively through comprehensive observing programmes conducted in the 1990s, allowing clarification of the major oceanographic processes involved in establishing the hydrography and circulation. An overview of the general circulation and hydrography in the ECS is given here, mainly based on the new observational results and with special attention to the Kuroshio bifurcation north-east of Taiwan and south-west of Kyushu and the major currents in the outer continental shelf. A new schematic circulation pattern of the ECS is sketched using these observations. The oceanographic conditions and fisheries environments of the ECS are not only seasonally variable because of the response of the basin to the seasonally varying atmospheric conditions, but also spatially and temporally complicated because of the wide spectrum of phenomena that coexist with various scales. [source] Weather regimes and their connection to the winter rainfall in PortugalINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2005J.A. Santos Abstract Wintertime rainfall over Portugal is strongly coupled with the large-scale atmospheric flow in the Euro-Atlantic sector. A K -means cluster analysis, on the space spanned by a subset of the empirical orthogonal functions of the daily mean sea-level pressure fields, is performed aiming to isolate the weather regimes responsible for the interannual variability of the winter precipitation. Each daily circulation pattern is keyed to a set of five weather regimes (C, W, NAO,, NAO+ and E). The dynamical structure of each regime substantiates the statistical properties of the respective rainfall distribution and validates the clustering technique. The C regime is related to low-pressure systems over the North Atlantic that induce southwesterly and westerly moist winds over the country. The W regime is characterized by westerly disturbed weather associated with low-pressure systems mainly located over northern Europe. The NAO, regime is manifested by weak low-pressure systems near Portugal. The NAO+ regime corresponds to a well-developed Azores high with generally settled and dry weather conditions. Finally, the E regime is related to anomalous strong easterly winds and rather dry conditions. Although the variability in the frequencies of occurrence of the C and NAO, regimes is largely dominant in the interannual variability of the winter rainfall throughout Portugal, the C regime is particularly meaningful over northern Portugal and the NAO, regime acquires higher relevance over southern Portugal. The inclusion of the W regime improves the description of the variability over northern and central Portugal. Dry weather conditions prevail in both the NAO+ and E regimes, with hardly any exceptions. The occurrence of the NAO+ and the NAO, regimes is also strongly coupled with the North Atlantic oscillation. Copyright © 2005 Royal Meteorological Society [source] Trends in the southern oscillation phenomenon and Australian rainfall and changes in their relationshipINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2004Ramasamy Suppiah Abstract An attempt has been made to investigate decadal-scale trends in Australian rainfall and in the southern oscillation index (SOI) and their influence on the relationship between them. Monthly rainfall data from high-quality stations in Australia (from 1900 to 1995), India, Sri Lanka and Tahiti are used. The relationship between the SOI and Australian rainfall is positive, but shows decadal-scale variations during the past century. Although there were extended and severe El Niño events in the early 1990s and in 1997, Australia did not experience the expected severe rainfall deficiencies characteristic of previous events. However, severe drought conditions over eastern Australia were associated with a moderate El Niño event during 2002,03. Long-term fluctuations of March,May (MAM) rainfall show high-frequency variations, but trends during June,August (JJA), September,November (SON) and December,February (DJF) show low-frequency or decadal-scale variations. Trends and multi-decadal fluctuations in all-Australian spring (SON) and summer (DJF) rainfall are strongly dominated by rainfall trend fluctuations in northern and eastern Australia. Austral summer rainfall shows an increasing trend during the 1980s and 1990s, particularly in Queensland and New South Wales, despite the occurrence of extended and severe El Niños. However, some parts of New South Wales and Queensland experienced severe rainfall deficiencies during 2002,03 in conjunction with an El Niño event. The relationship between the SOI and rainfall on the interannual time scale is strong when the SOI and rainfall follow the same direction, but it is weak when they follow opposite directions on a decadal-time scale. The poor correlation during the 1920s and 1930s was due to a slightly increasing trend in the SOI and a stronger decreasing trend in rainfall. A weakening in the relationship between the SOI and rainfall in recent years, after the mid-1970s, is due to a small increase in rainfall in the 1980s and 1990s and a strong decrease in the SOI. Rainfall trends were enhanced (stronger decreases or increases) when the influence of the SOI (or El Niño-southern oscillation (ENSO)) was removed. Enhanced increases and decreases are particularly strong during SON and DJF, when the ENSO phenomenon is at the mature stage and also the influence on Australian rainfall is strong. The increasing trend in rainfall during the 1980s and 1990s in some parts of eastern Australia and the decreasing trend in the SOI result in more rainfall for a given SOI compared with the same SOI during the previous period, i.e. before the mid-1970s. A similar analysis was carried out for two periods, before and after 1972, for Tahiti, India and Sri Lanka. The upward or downward shift in regression lines is very clear during the season, that shows a strong relationship between rainfall and the SOI. Moreover, strengthening or weakening of the relationship between rainfall and the SOI is largely dependent on their multi-decadal variations and trends during the past century. Increases in rainfall during the 1980s and the 1990s and decreases in the SOI have weakened their relationship, both in Australia and India. Such a relationship gives more rainfall for a given SOI after 1973. The pattern was reversed for Sri Lanka, where rainfall during the second intermonsoon season has decreased. Analyses of trends in temperature at Darwin and Tahiti and of rainfall over Australia, India, Tahiti and Sri Lanka suggest a regional-scale change in climate, whereas the SOI reflects a change in the large-scale circulation pattern over the Indo-Pacific region after the mid-1970s. Copyright © 2004 Royal Meteorological Society [source] Changes in seasonal mean maximum air temperature in Romania and their connection with large-scale circulationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2002Rodica Tomozeiu Abstract This paper investigates the temporal and spatial variability of the seasonal mean of maximum air temperature in Romania and its links with the large,scale atmospheric circulation. The Romanian data sets are represented by time series at 14 stations. The large-scale parameters are represented by the observed sea-level pressure (SLP) and geopotential height at 500 hPa (Z500). The period analysed was 1922,98 for winter and 1960,98 for all seasons. Before analysis, the original temperature data were tested to detect for inhomogeneity using the standard normal homogeneity test. Empirical orthogonal functions (EOFs) were used to analyse the spatial and temporal variability of the local and large-scale parameters and to eliminate noise from the original data set. The time series associated with the first EOF pattern of the SLP and mean maximum temperature in Romania were analysed from trend and shifts point of view using the Pettitt and Mann,Kendall tests respectively. The covariance map computed using the Z500 and the seasonal mean of maximum temperature in Romania were used as additional methods to identify the large-scale circulation patterns influencing the local variability. Significant increasing trends were found for winter and summer mean maximum temperature in Romania, with upward shifts around 1947 and 1985 respectively. During autumn, a decreasing trend with a downward shift around 1969 was detected. These changes seem to be real, since they are connected to similar changes in the large-scale circulation. So, the intensification of the southwesterly circulation over Europe since 1933 overlapped with the enhancement of westerly circulation after the 1940s could be the reason for the change in winter mean maximum temperature. The slight weakening of the southwesterly circulation during autumn could be one of the reasons for the decrease in the regime of the mean maximum temperature for autumn seasons. Additionally, the covariance map technique reveals the influence of the North Atlantic oscillation in winter, East Atlantic Jet in summer and Scandinavian (or Euroasia-1) circulation pattern in autumn upon mean maximum air temperature. Copyright © 2002 Royal Meteorological Society. [source] Effects of atmospheric circulation on ice conditions in the southern Baltic coastal lagoonsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2001Józef Piotr Girjatowicz Abstract Relationships between atmospheric circulation patterns and ice conditions in the southern Baltic coastal lagoons were explored. Ice data consisted of number of ice days (L) and duration of ice season (S) in the Szczecin Lagoon (off Karnin), the Puck Bay (off Puck) and the Vistula Lagoon (off Krasnoflotskoye) from 1950/1951 to 1989/1990. Atmospheric circulation patterns for the period studied were extracted from Lity,ski's ,Calendar of atmospheric circulation types' developed at the Institute of Meteorology and Water Management (IMWM). A circulation pattern was identified by three numerical parameters: the zonal circulation index, the meridional circulation index, both pertaining to a zone delimited by coordinates 40,60°N, 0,35°E, and the surface pressure index for Warsaw. The number of days with individual atmospheric circulation patterns occurring from October to March was calculated. Subsequently, the selected patterns were combined by wind direction sectors and several month-long periods that most closely correlated with ice conditions. The highest linear correlation coefficients (r>0.8) were obtained for the relationship between the number of days with winds from the east from December to February and December to March and the winter number of ice days (L). Somewhat higher were multiple correlation coefficients with winds from the east and west as circulation type predictors. Slightly lower correlation coefficients for the sectors and circulation periods mentioned were obtained for the duration of the ice season (S), although some of the coefficients were significant even at the probability level of ,=0.01. Higher correlation coefficients were obtained for correlations involving ,cold' circulation patterns (sector NE+E+SE winds) and ice conditions than for those involving ,warm' patterns (sector SW+W+NW). Copyright © 2001 Royal Meteorological Society [source] Evidence for Changing Flood Risk in New England Since the Late 20th Century,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2009Mathias J. Collins Abstract:, Long-term flow records for watersheds with minimal human influence have shown trends in recent decades toward increasing streamflow at regional and national scales, especially for low flow quantiles like the annual minimum and annual median flows. Trends for high flow quantiles are less clear, despite recent research showing increased precipitation in the conterminous United States over the last century that has been brought about primarily by an increased frequency and intensity of events in the upper 10th percentile of the daily precipitation distribution , particularly in the Northeast. This study investigates trends in 28 long-term annual flood series for New England watersheds with dominantly natural streamflow. The flood series are an average of 75 years in length and are continuous through 2006. Twenty-five series show upward trends via the nonparametric Mann-Kendall test, 40% (10) of which are statistically significant (p < 0.1). Moreover, an average standardized departures series for 23 of the study gages indicates that increasing flood magnitudes in New England occurred as a step change around 1970. The timing of this is broadly synchronous with a phase change in the low frequency variability of the North Atlantic Oscillation, a prominent upper atmospheric circulation pattern that is known to effect climate variability along the United States east coast. Identifiable hydroclimatic shifts should be considered when the affected flow records are used for flood frequency analyses. Special treatment of the flood series can improve the analyses and provide better estimates of flood magnitudes and frequencies under the prevailing hydroclimatic condition. [source] A HYDROCLIMATOLOGICAL ANALYSIS OF THE RED RWER OF THE NORTH SNOWMELT FLOOD CATASTROPHE OF 1997,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2001Paul E. Todhunter ABSTRACT: The flood hydroclimatology of the Grand Forks flood of April 1997, the most costly flood on a per capita basis for a major metropolitan area in United States history, is analyzed in terms of the natural processes that control spring snowmelt flooding in the region. The geomorphological characteristics of the basin are reviewed, and an integrated assessment of the hydroclimatological conditions during the winter of 1996 to 1997 is presented to gain a real-world understanding of the physical basis of this catastrophic flood event. The Grand Forks flood resulted from the principal flood-producing factors occurring at either historic or extreme levels, or at levels conducive to severe flooding. Above normal fall precipitation increased the fall soil moisture storage and reduced the spring soil moisture storage potential. A concrete frost layer developed that effectively reduced the soil infiltration capacity to zero. Record snowfall totals and snow cover depths occurred across the basin because of the unusual persistence of a blocking high circulation pattern throughout the winter. A severe, late spring blizzard delayed the snowmelt season and replenished the snow cover to record levels for early April. This blizzard was followed by a sudden transition to an extreme late season thaw due to the abrupt breakdown of the blocking circulation pattern. The presence of river ice contributed to backwater effects and affected the timing of tributary inflows to the main stem of the Red River. Only the absence of spring rains prevented an even more catastrophic flood disaster from taking place. This paper contributes to our understanding of the flood hydroclimatology of catastrophic flood events in an unusual flood hazard region that possesses relatively flat terrain, a north-flowing river, and an annual peak discharge time series dominated by spring snowmelt floods. [source] A broad transition zone between an inner Baltic hybrid swarm and a pure North Sea subspecies of Macoma balthica (Mollusca, Bivalvia)MOLECULAR ECOLOGY, Issue 6 2008RAISA NIKULA Abstract The populations of the bivalve clam Macoma balthica in the low-salinity Northern Baltic Sea represent an admixture of two strongly diverged genomic origins, the Pacific Macoma balthica balthica (approx. 60% genomic contribution) and Atlantic Macoma balthica rubra (40%). Using allozyme and mtDNA characters, we describe the broad transition from this hybrid swarm to the pure M. b. rubra in the saline North Sea waters, spanning hundreds of kilometre distance. The zone is centred in the strong salinity gradient of the narrow Öresund strait and in the adjacent Western Baltic. Yet the multilocus clines show no simple and smoothly monotonic gradation: they involve local reversals and strong differences between neighbouring populations. The transitions in different characters are not strictly coincident, and the extent of introgression varies among loci. The Atlantic influence extends further into the Baltic in samples from the southern and eastern Baltic coasts than on the western coast, and further in deeper bottoms than at shallow (< 1 m) sites. This fits with the counterclockwise net circulation pattern and with a presumably weaker salinity barrier for invading Atlantic type larvae in saline deeper water, and corresponding facilitation of outwards drift of Baltic larvae in diluted surface waters. Genotypic disequilibria were strong particularly in the shallow-water samples of the steepest transition zone. This suggests larval mixing from different sources and limited interbreeding in that area, which makes a stark contrast to the evidence of thorough amalgamation of the distinct genomic origins in the inner Baltic hybrid swarm of equilibrium structure. [source] Viruses and atypical bacteria associated with asthma exacerbations in hospitalized children,PEDIATRIC PULMONOLOGY, Issue 6 2010Alberto F. Maffey MD Abstract Objectives and Working Hypothesis To evaluate the prevalence of respiratory viruses Mycoplasma pneumoniae and Chlamydophila pneumoniae and gain insight into their seasonal circulation pattern in children with acute asthma exacerbations in a temperate southern hemisphere region. Study Design Patients hospitalized between 3 months and 16 years of age were included in a 1-year prospective, observational, cross-sectional study. Respiratory secretions were collected and the presence of different viruses and atypical bacteria analyzed by immunofluorescence and polymerase chain reaction. Results Two hundred nine patients (118 females) aged (mean,±,SD) 4.4,±,4 years were included. A potential causative agent was detected in 78% of the patients. The most frequently detected viruses were respiratory syncytial virus (HRSV) (n,=,85; 40%) and rhinovirus (HRV) (n,=,52; 24.5%); M. pneumoniae and C. pneumoniae were detected in 4.5% and 2% of the cases, respectively. Patients with HRSV (vs. HRV) were hospitalized for a longer time (6.7 vs. 5.2 days, P,=,0.012), required more days of oxygen supply (5.1 vs. 3.4, P,=,0.005), had a longer duration of the exacerbation before hospitalization (3.6 vs. 1.9 days, P,=,0.001) and were younger (3.7 vs. 5.1 years, P,=,0.012). Three peaks of admissions were observed. A first peak (early autumn) caused by HRV, a second peak (winter) caused mainly by HRSV and a third one (spring), caused by HRSV, an increase in HMPV together with a second outbreak of HRV. Conclusions Children with an acute asthma exacerbation presented a high prevalence of respiratory viruses. Most hospitalizations corresponded to seasonal increases in prevalence of HRV and HRSV. Pediatr Pulmonol. 2010; 45:619,625. © 2010 Wiley-Liss, Inc. [source] Intermediary Spleen Microvasculature in Canis familiaris, Morphological Evidences of a Closed and Open TypeANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 5 2003G. Alexandre-Pires Summary Numerous studies have been made regarding circulation via the red pulp of the spleen, and intense controversy surrounds the question as to whether or not endothelial continuity exists between arterial and venous vessels. Aware of this intense controversy, and in order to perform investigation over the spleen of dogs infected with a parasitic disease (future reports shall be done), the authors studied the vascularization of the normal dog spleen in order to define its normal pattern and evaluate the eventual changes of the circulation pattern under the parasitic condition. These studies led us to report, unequivocally, using complementary vascular replective techniques, that the normal dog's intermediary circulation is morphologically closed and of the open kind also. These findings are contrary to the thesis that defends the existence of a physiologically closed and morphologically open circulation in the dog spleen. Lymphatic vessels in the spleen of the dog are also demonstrated. [source] A Bayesian hierarchical model for local precipitation by downscaling large-scale atmospheric circulation patternsENVIRONMETRICS, Issue 7 2006Jorge M. Mendes Abstract Precipitation over the Western part of Iberian Peninsula is known to be related to the large-scale sea level pressure field and thus to advection of humidity into this area. The major problem is to downscale this synoptic atmospheric information to local daily precipitation patterns. One way to handle this problem is by weather-state models, where, based on the pressure field, each day is classified into a weather state and precipitation is then modeled within each weather state via multivariate distributions. In this paper, we propose a spatiotemporal Bayesian hierarchical model for precipitation. Basic objective and novelty of the paper is to capture and model the essential spatiotemporal relationships that exist between large-scale sea level pressure field and local daily precipitation. A specific local spatial ordering that mimics the essential large-scale patterns is used in the likelihood. The model is then applied to a network of rain gauge stations in the river Tagus valley. The inference is then carried out using appropriate MCMC methods. Copyright © 2006 John Wiley & Sons, Ltd. [source] Prediction of sea surface temperature from the global historical climatology network dataENVIRONMETRICS, Issue 3 2004Samuel S. P. Shen Abstract This article describes a spatial prediction method that predicts the monthly sea surface temperature (SST) anomaly field from the land only data. The land data are from the Global Historical Climatology Network (GHCN). The prediction period is 1880,1999 and the prediction ocean domain extends from 60°S to 60°N with a spatial resolution 5°×5°. The prediction method is a regression over the basis of empirical orthogonal functions (EOFs). The EOFs are computed from the following data sets: (a) the Climate Prediction Center's optimally interpolated sea surface temperature (OI/SST) data (1982,1999); (b) the National Climatic Data Center's blended product of land-surface air temperature (1992,1999) produced from combining the Special Satellite Microwave Imager and GHCN; and (c) the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis data (1982,1999). The optimal prediction method minimizes the first- M -mode mean square error between the true and predicted anomalies over both land and ocean. In the optimization process, the data errors of the GHCN boxes are used, and their contribution to the prediction error is taken into account. The area-averaged root mean square error of prediction is calculated. Numerical experiments demonstrate that this EOF prediction method can accurately recover the global SST anomalies during some circulation patterns and add value to the SST bias correction in the early history of SST observations and the validation of general circulation models. Our results show that (i) the land only data can accurately predict the SST anomaly in the El Nino months when the temperature anomaly structure has very large correlation scales, and (ii) the predictions for La Nina, neutral, or transient months require more EOF modes because of the presence of the small scale structures in the anomaly field. Copyright © 2004 John Wiley & Sons, Ltd. [source] From egg to juvenile in the Bay of Biscay: spatial patterns of anchovy (Engraulis encrasicolus) recruitment in a non-upwelling regionFISHERIES OCEANOGRAPHY, Issue 6 2008XABIER IRIGOIEN Abstract In this study the spatial distribution of eggs, larvae and juveniles of European anchovy (Engraulis encrasicolus) was followed in 2004 and 2005 during three consecutive cruises each year in spring,summer to test what the limits of retention are in a non-upwelling area. Eggs, small larvae and large juveniles were mainly distributed over the shelf, whereas large larvae and small juveniles were found mainly off the shelf. Although overall distributions were similar, the 2 yr differed in that there was more of a coastal distribution of individuals in 2004, whereas in 2005 more individuals were found off the shelf. There were no significant differences in the length,weight relationships for individuals found on and off the shelf or between years. The correspondence in circulation patterns and the lack of difference in the length,weight relationships suggest that a single population is present, larvae drifting off the shelf due to currents and returning as mobile juveniles. Quantile regression analysis of the long-term recruitment index suggests that transport off the shelf may favour good recruitments. This would suggest that in non-upwelling regions the retention area resulting in good recruitment may not be restricted to the shelf. [source] Climate change and abundance of the Atlantic-Iberian sardine (Sardina pilchardus)FISHERIES OCEANOGRAPHY, Issue 2 2004C. Guisande Abstract Climatic warming is affecting oceanic circulation patterns in coastal upwelling areas, but the impact of this climatic change on pelagic fish populations remains unclear. From juvenile landings collected over 38 years, the thresholds of environmental factors were determined that limited the optimal environmental window (OEW) for sardine (Sardina pilchardus recruitment success in the northwestern Iberian peninsula. The environmental factors considered were: water column stability in February, offshore water transport in March,April (QxMA), upwelling intensity in the preceding year from May to August (QxMJJA), and the winter North Atlantic Oscillation (NAO) index. From 1875 to the mid-1920s, the mean number of years within the OEW was relatively constant. However, since the mid-1920s, there have been oscillations and alternating decades with high and low number of years within the OEW, which were related to oscillations in sardine landings. From 1906 to 2000, there were four record, low sardine catches in the 1920s, 1950s, 1970s and 1990s, related to a high number of successive years with prevailing conditions out of the OEW. From 1875 to the present, a high year-to-year variation of the NAO, QxMJJA and water stability in February was observed, although with mean values usually within the OEW. The collapse in the 1950s was related, partly, to successive years with low QxMJJA. Successive years with high NAO values may be related to the collapse of the sardine fishery in the 1990s. QxMA has been the most significant factor controlling SRS in this area, being the factor related to the low catches observed in the 1920s, 1950s and 1970s. Water stability was not responsible for any of the collapses observed, but since the 1920s, there has been a significant trend toward decreasing water column stability before the onset of the spring bloom. [source] The effects of diel changes in circulation and mixing on the longitudinal distribution of phytoplankton in a canyon-shaped Mediterranean reservoirFRESHWATER BIOLOGY, Issue 9 2010JAVIER VIDAL Summary 1. The near-surface distribution of phytoplankton cells along the thalweg of a canyon-shaped reservoir (El Gergal, southern Spain) during two surveys is described and interpreted as the result of time-varying large-scale circulation patterns, vertical mixing processes and the physiological capacity of algal cells to regulate its position in the water column. 2. Vertical gradients of chlorophyll-a concentration developed in the water column during the day but disappeared at night, as a result of the shoaling and deepening of the diurnal mixed layer (dml). The changes in the depth of the dml are largely controlled in El Gergal by convectively driven mixing processes. The longitudinal circulation changes, in turn, as a result of weak and diurnal land-sea breezes. The distribution of algal cells was patchy at all times but did not change during any of the surveys. 3. An expression is proposed to estimate time scales for the development of horizontal patchiness TP based on simple concepts of transport. It is shown that TP is in the order of a week, indicating that horizontal patchiness does not respond immediately to hourly changes in the controlling factors. The magnitude of TP, though, depends on how the vertical distribution of chlorophyll-a and longitudinal currents change on subdiurnal time scales. In particular, TP is sensitive to the lag existing between the momentum and heat fluxes through the free surface, driving circulation and vertical mixing. [source] Analysis of snow cover variability and change in Québec, 1948,2005HYDROLOGICAL PROCESSES, Issue 14 2010Ross D. Brown Abstract The spatial and temporal characteristics of annual maximum snow water equivalent (SWEmax) and fall and spring snow cover duration (SCD) were analysed over Québec and adjacent area for snow seasons 1948/1949,2004/2005 using reconstructed daily snow depth and SWE. Snow cover variability in Québec was found to be significantly correlated with most of the major atmospheric circulation patterns affecting the climate of eastern North America but the influence was characterized by strong multidecadal-scale variability. The strongest and most consistent relationship was observed between the Pacific Decadal Oscillation (PDO) and fall SCD variability over western Québec. El Niño-Southern Oscillation (ENSO) was found to have a limited impact on Québec snow cover. Evidence was found for a shift in circulation over the study region around 1980 associated with an abrupt increase in sea level pressure (SLP) and decreases in winter precipitation, snow depth and SWE over much of southern Québec, as well as changes in the atmospheric patterns with significant links to snow cover variability. Trend analysis of the reconstructed snow cover over 1948,2005 provided evidence of a clear north,south gradient in SWEmax and spring SCD with significant local decreases over southern Québec and significant local increases over north-central Québec. The increase in SWEmax over northern Québec is consistent with proxy data (lake levels, tree growth forms, permafrost temperatures), with hemispheric-wide trends of increasing precipitation over higher latitudes, and with projections of global climate models (GCMs). Copyright © 2010 Her Majesty the Queen in right of Canada. Published by John Wiley & Sons. Ltd [source] Long-term final void salinity prediction for a post-mining landscape in the Hunter Valley, New South Wales, AustraliaHYDROLOGICAL PROCESSES, Issue 2 2005Dr G. R. Hancock Abstract Opencast mining alters surface and subsurface hydrology of a landscape both during and post-mining. At mine closure, following opencast mining in mines with low overburden to coal ratios, a void is left in the final landform. This final void is the location of the active mine pit at closure. Voids are generally not infilled within the mines' lifetime, because of the prohibitive cost of earthwork operations, and they become post-mining water bodies or pit lakes. Water quality is a significant issue for pit lakes. Groundwater within coal seams and associated rocks can be saline, depending on the nature of the strata and groundwater circulation patterns. This groundwater may be preferentially drawn to and collected in the final void. Surface runoff to the void will not only collect salts from rainfall and atmospheric fallout, but also from the ground surface and the weathering of fresh rock. As the void water level rises, its evaporative surface area increases, concentrating salts that are held in solution. This paper presents a study of the long term, water quality trends in a post-mining final void in the Hunter Valley, New South Wales, Australia. This process is complex and occurs long term, and modelling offers the only method of evaluating water quality. Using available geochemical, climate and hydrogeological data as inputs into a mass-balance model, water quality in the final void was found to increase rapidly in salinity through time (2452 to 8909 mg l,1 over 500 years) as evaporation concentrates the salt in the void and regional groundwater containing high loads of salt continues to flow into the void. Copyright © 2004 John Wiley & Sons, Ltd. [source] Godunov-type adaptive grid model of wave,current interaction at cuspate beachesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2004Benedict D. Rogers Abstract This paper presents a second-order accurate Godunov-type numerical scheme for depth- and period-averaged wave,current interaction. A flux Jacobian is derived for the wave conservation equations and its eigensystem determined, enabling Roe's approximate Riemann solver to be used to evaluate convective fluxes. Dynamically adaptive quadtree grids are used to focus on local hydrodynamic features, where sharp gradients occur in the flow variables. Adaptation criteria based on depth-averaged vorticity, wave-height gradient, wave steepness and the magnitude of velocity gradients are found to produce accurate solutions for nearshore circulation at a half-sinusoidal beach. However, the simultaneous combination of two or more separate criteria produces numerical instability and interference unless all criteria are satisfied for mesh depletion. Simulations of wave,current interaction at a multi-cusped beach match laboratory data from the United Kingdom Coastal Research Facility (UKCRF). A parameter study demonstrates the sensitivity of nearshore flow patterns to changes in relative cusp height, angle of wave incidence, bed roughness, offshore wave height and assumed turbulent eddy viscosity. Only a small deviation from normal wave incidence is required to initiate a meandering longshore current. Nearshore circulation patterns are highly dependent on the offshore wave height. Reduction of the assumed eddy viscosity parameter causes the primary circulation cells for normally incident waves to increase in strength whilst producing rip-like currents cutting diagonally across the surf zone. Copyright © 2004 John Wiley & Sons, Ltd. [source] Changes in hot days and heat waves in China during 1961,2007INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2010Ting Ding Abstract Based on the daily maximum temperature (DMT) records at 512 stations during 1961,2007, the geographical patterns and temporal variations of hot days (HDs) and heat waves (HWs, including those persisting for 3,5 days and longer) over mainland China were studied. The HD (and hence HW) was defined in two ways, one by an absolute criterion, DMT > 35 °C, as applied in the nationwide meteorological agencies and another in a relative sense, DMT > the 90th percentile threshold of a local daily temperature distribution around the day. Two centers of high frequencies (over 5 days per year) of the absolute HDs during June,September were found in the regions of Xinjiang and the mid-lower reaches of the Yangtze River. The highest frequencies of the absolute HWs were about 1.5 times per year in the Xinjiang region and to the south of the mid-lower reaches of the Yangtze River. The frequencies of the relative HWs were about 1,1.5 times per year in most of China. The HDs and HWs increased significantly during the studied period in most of China, especially over the southeastern coast and northern China (by over 4 days per decade for relative HDs and 0.4 times per decade for relative HWs), but decreased significantly at some stations in the lower reaches of the Yellow River. Over most of China except northwestern China, the frequency of HDs was high during the 1960s,1970s, low in the 1980s, and high afterwards, with strong interannual variations. A remarkable increasing trend of HDs occurred after the 1990s in all regions. The changes in HDs and HWs were closely related to those in rain days and atmospheric circulation patterns at the interannual and interdecadal scales. Copyright © 2009 Royal Meteorological Society [source] Early 20th century Arctic warming in retrospectINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2010Kevin R. Wood Abstract The major early 20th century climatic fluctuation (,1920,1940) has been the subject of scientific enquiry from the time it was detected in the 1920s. The papers of scientists who studied the event first-hand have faded into obscurity but their insights are relevant today. We review this event through a rediscovery of early research and new assessments of the instrumental record. Much of the inter-annual to decadal scale variability in surface air temperature (SAT) anomaly patterns and related ecosystem effects in the Arctic and elsewhere can be attributed to the superposition of leading modes of variability in the atmospheric circulation. Meridional circulation patterns were an important factor in the high latitudes of the North Atlantic during the early climatic fluctuation. Sea surface temperature (SST) anomalies that appeared during this period were congruent with low-frequency variability in the climate system but were themselves most likely the result of anomalous forcing by the atmosphere. The high-resolution data necessary to verify this hypothesis are lacking, but the consistency of multiple lines of evidence provides strong support. Our findings indicate that early climatic fluctuation is best interpreted as a large but random climate excursion imposed on top of the steadily rising global mean temperature associated with anthropogenic forcing. Copyright © 2009 Royal Meteorological Society [source] Synoptic forcing of precipitation in the Mackenzie and Yukon River basinsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2010Elizabeth N. Cassano Abstract The relationship between near-surface atmospheric circulation, as characterized by sea level pressure patterns, and precipitation in the Mackenzie and Yukon River basins is presented. A synoptic climatology of sea level pressure patterns based on daily sea level pressure anomalies from the ERA40 reanalysis dataset was created using the method of self-organizing maps. This objective analysis identified all major near-surface atmospheric circulation patterns in the region and illustrated the change in dominant circulation patterns throughout the seasons, with strong Aleutian low patterns dominant in the winter and patterns characterized by low pressure over land areas and the Beaufort/Chukchi Seas in the summer. These synoptic patterns were then related to daily precipitation in the Mackenzie and Yukon River basins. The largest daily precipitation values, for both the Mackenzie and Yukon basins, were associated with patterns that occur most frequently in the summer, likely associated with increased frequency of cyclones and convective events that occur over land in that season. During winter, the largest positive precipitation anomalies were along the coastal mountain range in southeastern Alaska associated with Aleutian lows bringing warm, moist flow from the south resulting in upslope flow on the windward side of these mountains. These patterns were responsible for many of the large precipitation events in the winter in the Mackenzie basin. The largest precipitation events in the winter in the Yukon basin occurred with patterns that have a low pressure centre to the southwest of the basin. This synoptic pattern results in southerly flow advecting moisture into the basin to the west of the higher topography which bounds much of the southern boundary of the Yukon watershed. Copyright © 2009 Royal Meteorological Society [source] China's snow disaster in 2008, who is the principal player?INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2009Gao Hui Abstract The unprecedented snow disaster in January 2008 brought serious human and economic losses to China. It has been suggested that the La Nina event is the principal cause. But analysis indicates that in December 2007, the circulation patterns in the tropical regions are quite similar with those in January 2008. In contrast large differences existed at high latitudes, especially the Siberia high (SH) and the north polar vortex (NPV). The differences can also be found between other extreme heavy and light snow years. In the extreme heavy (light) snow years, the SH is stronger (weaker) and the NPV is deeper (shallower). But these extreme snow events don't correspond to ENSO events well. Statistical results also indicate that both the SH and the NPV are independent of ENSO. So, rather than the La Nina event, the abnormal circulations at the high latitudes may play a more crucial role in making this snow disaster. Copyright © 2009 Royal Meteorological Society [source] Long-term variability in precipitation and streamflow in Iceland and relations to atmospheric circulationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2009Jóna Finndís Jónsdóttir Abstract How the variability of the atmospheric circulation affects precipitation in Iceland is not completely understood. Also, the sea surface temperature (SST) has a strong influence on the temperature over the country, and thereby, snow and glacial melt. This study, therefore, aims at explaining how atmospheric circulation and sea surface temperature influence seasonal and annual precipitation, and, consequently, runoff in Iceland. Empirical orthogonal function (EOF) analysis is performed on annual and seasonal time series of precipitation and discharge to identify their key modes of variability during the period 1966,2004. The correlation between the time series of each EOF mode with individual time series of sea level pressure (SLP), air temperature and SST was then evaluated. The analyses evidenced how large-scale climate variables are connected to the regional precipitation and runoff in Iceland. They showed that the strength of the polar vortex may be, at least, as important for the precipitation in some areas of Iceland as the strength of the Icelandic Low (IL). Moreover, the location of the semi-permanent IL often defines the predominant wind direction over the country and, as such, the regions of preferred precipitation. Since the watersheds act as large precipitation gauges with response patterns depending on the geology and glaciers, the variability of the annual discharge closely resembles the variability of precipitation, except for the glacial rivers. Glacial melt is highly correlated to air temperature and SST, and the spring discharge is affected by winter and spring temperatures. The results also revealed that Icelandic hydrological conditions in the spring can be forecasted by precipitation and temperature of the autumn and winter seasons, as well as by the general prevalent circulation patterns. Additionally, a potential for seasonal forecast of precipitation, and river discharge in other seasons was identified, particularly if seasonal forecast of SLP is available. Copyright © 2008 Royal Meteorological Society [source] Statistical downscaling of extremes of daily precipitation and temperature and construction of their future scenariosINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2008Yeshewatesfa Hundecha Abstract Two statistical downscaling methods have been tested in terms of their ability to construct indices of extremes of daily precipitation and temperatures from large-scale atmospheric variables with the aim of developing a tool for the construction of future scenarios of the extremes. One of the methods implements an approach for constructing seasonal indices of extremes of precipitation and temperature from seasonal measures of large-scale variables, while the other method implements a stochastic model for generating daily series of precipitation and temperature whose parameters are conditioned on large-scale circulation patterns. While both models generally tend to perform fairly well in reproducing indices of precipitation in winter, their performance for the summer season is not attractive. For indices of temperature, the performance of both models is better than the corresponding performance for indices of precipitation and the seasonal variation in performance is less prominent. The models were applied to construct scenarios of the extremes for the end of the 21st century using predictor sets simulated by the Hadley Centre GCM (HadAM3P) forced by two of the special report on emission scenarios (SRES) emission scenarios. Both models project an increase in both the mean daily minimum and mean daily maximum temperatures for future climate change scenarios in all seasons. The summer increase is accompanied by an increase in the inter-annual variability of the temperatures. On the other hand, they show consistency in the direction of the projected changes in indices of precipitation only in winter, where they projected an increase in both the magnitude and frequency of extremes as well as the mean precipitation. The disparity in the changes simulated by the two models revealed the existence of considerable inter-model uncertainty in predicting changes for future climate. Copyright © 2007 Royal Meteorological Society [source] Statistical downscaling model based on canonical correlation analysis for winter extreme precipitation events in the Emilia-Romagna regionINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2008A. Busuioc Abstract Optimum statistical downscaling models for three winter precipitation indices in the Emilia-Romagna region, especially related to extreme events, were investigated. For this purpose, the indices referring to the number of events exceeding the long-term 90 percentile of rainy days, simple daily intensity and maximum number of consecutive dry days were calculated as spatial averages over homogeneous sub-regions identified by the cluster analysis. The statistical downscaling model (SDM) based on the canonical correlation analysis (CCA) was used as downscaling procedure. The CCA was also used to understand the large-/regional-scale mechanisms controlling precipitation variability across the analysed area, especially with respect to extreme events. The dynamic (mean sea-level pressure-SLP) and thermodynamic (potential instability-,Q and specific humidity-SH) variables were considered as predictors (either individually or together). The large-scale SLP can be considered a good predictor for all sub-regions in the dry index case and for two sub-regions in the case of the other two indices, showing the importance of dynamical forcing in these cases. Potential instability is the best predictor for the highest mountain region in the case of heavy rainfall frequency, when it can be considered as a single predictor. The combination of dynamic and thermodynamic predictors improves the SDM's skill for all sub-regions in the dry index case and for some sub-regions in the simple daily intensity index case. The selected SDMs are stable in time only in terms of correlation coefficient for all sub-regions for which they are skilful and only for some sub-regions in terms of explained variance. The reasons are linked to the changes in the atmospheric circulation patterns influencing the local rainfall variability in Emilia-Romagna as well as the differences in temporal variability over some sub-regions and sub-intervals. It was concluded that the average skill over an ensemble of the most skilful and stable SDMs for each region/sub-interval gives more consistent results. Copyright © 2007 Royal Meteorological Society [source] Time variations of the effects of circulation variability modes on European temperature and precipitation in winterINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2008Romana Beranová Abstract Five modes of variability are identified in winter monthly mean 500 hPa heights over the Euro-Atlantic sector by rotated principal component analysis. Time variations of the effects of the modes on temperature and precipitation at more than 100 European stations are examined for period 1958,1998. Time variations are investigated by running correlations with the 15-year window. At most of the stations, the correlations with circulation patterns vary considerably in time, both for temperature and precipitation. The spatial structure of the variations is assessed by cluster analysis of time variations of correlations. The groupings together with changes in the intensity and position of the circulation modes suggest possible mechanisms of the time variations in the circulation-to-climate effects. Copyright © 2007 Royal Meteorological Society [source] The influence of atmospheric circulation at different spatial scales on winter drought variability through a semi-arid climatic gradient in Northeast SpainINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2006Sergio M. Vicente-Serrano Abstract This paper analyses the spatial and temporal variability of winter droughts in a semi-arid geographic gradient in Northeast Spain, from the Pyrenees in the north to the Mediterranean coastland in the south. Droughts that occurred between 1952 and 1999 were analysed by means of the Standardised Precipitation Index (SPI). The influence of the weather-type frequency and of the general North Atlantic atmospheric circulation patterns was analysed. The results indicate that winter droughts show an important spatial variability in the study area, differentiating three well-defined patterns. These correspond to the Pyrenees, the centre of the Ebro Valley, and the Mediterranean coastland. General negative trends in winter SPI have been found, which are indicative of the increase in winter drought conditions in the study area. Nevertheless, important spatial differences have also been recorded. Dominant north,south gradients in the influence of weather types are shown. Moreover, the negative trends in winter-SPI values agree with the negative trend in the frequency of the weather types prone to cause precipitation, such as the C, SW and W weather types and the increase in the frequency of A weather types. Nevertheless, in the Mediterranean coastland, the positive trend in SPI values agrees with the increase in the frequency of weather types of the east (E, SE), which are prone to cause precipitation in this area. Interannual variations in the frequency of the different weather types have been highly determined by different general atmospheric circulation patterns, mainly the North Atlantic Oscillation (NAO). Nevertheless, the correlation between the time series of weather-type frequency and the winter SPI is higher than that found between the SPI and the NAO. Thus, although the interannual NAO variability explains a high percentage of the interannual differences in the frequency of different weather types, it is not sufficient to explain the spatial and temporal variability of droughts, which respond better to atmospheric variability at more detailed (synoptic) spatial scales. Copyright © 2006 Royal Meteorological Society. [source] Synoptic climatology of extreme fire-weather conditions across the southwest United StatesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2006Michael A. Crimmins Abstract Extreme fire-weather conditions are usually thought of as discrete events rather than part of a continuum of meteorological and climatological variability. This study uses a synoptic climatological approach (weather typing) to examine the seasonal climatology of extreme fire-weather conditions across the southwest United States (Arizona and New Mexico) during the period of 1988,2003. Three key circulation patterns representing broad southwesterly flow and large geopotential height gradients are associated with over 80% of the extreme fire-weather days identified in this study. Seasonal changes in relative humidity levels, strength of height gradient, and geopotential heights all modulate the relationship between these key circulation patterns and extreme fire-weather days. Examination of daily incident summaries for three recent wildfires (May 2000, June 2002 and June 2003) shows that wildfire activity can be strongly regulated by these critical fire-weather circulation patterns. Copyright © 2006 Royal Meteorological Society. [source] Responses of large volcanic eruptions in the instrumental and documentary climatic data over Central EuropeINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2006Jan Písek Abstract Responses of large volcanic eruptions in selected long temperature series from Austria, the Czech Republic and Germany as well as in three global radiation series in Central Europe are studied. In the example of seven large tropical eruptions (Krakatau 1883; Pelée, Soufriére and Santa María 1902; Agung, 1963; El Chichón, 1982; Mt Pinatubo, 1991) it has been demonstrated that volcanic signal in regional series is not so strongly expressed as in the hemispheric scale owing to different local effects and circulation patterns. This is also valid in the case of two further discussed eruptions of Tambora (1815) and Katmai (1912). The responses of eruptions in areas closer to Central Europe such as Iceland or Italy are more important. In nine analysed cases with VEI = 4,5 with a single exception of the Hekla eruption (1917), cold seasons were observed to follow the eruption. Responses to the Lakagígar eruption (1783) of Iceland with important impacts are also discussed in detail. Moreover, correlation between temperatures (annual and winter half-year series) and NAOI is prevailingly smaller for the period following eruptions than in the period preceding eruptions. The importance of documentary evidence as a valuable source of the information about the impacts of volcanic eruptions is demonstrated. Copyright © 2006 Royal Meteorological Society. [source] | |||||||||||||||||||