Descripción: This work proposes to employ the number of dry days (days without precipitation) as a variable of study, and to analyse their spatial and temporal variability in Argentina. Climatological aspects of dry days, such as their annual mean values and its seasonal cycle, were discussed and compared with precipitation features in the country. Linear trends in the annual number of dry days (ANDD) were identified for the period 1960-2005. Most of the regions exhibited decreasing trends, but few stations showed significant ones. The most important trends were present in the Central-West region and over the Patagonian coast and their magnitudes indicated a decrease of two to six dry days per decade. These trends coincide with the observed increase of accumulated precipitation in part of the country during the second half of the 20th century. To identify long-term fluctuations in the ANDD, a low pass filter, a wavelet analysis and a cubic polynomial fit was applied to the longest time series of the selected locations. Through these methodologies, periodicities were identified in the inter-annual and inter-decadal ranges for the last 80 years. The most important significant cycles were observed in the range of 10-24 years, but also, depending on the region, significant inter-annual variations were found. © 2012 Royal Meteorological Society.

Descripción: Daily station precipitation totals are used to develop a gridded dataset for the region (14°-40°S, 45°-70°W) on a 0.5° × 0.5° latitude/longitude grid, primarily for comparison with regional climate model (RCM) simulations. The gridded dataset covers the period 1961-2000. Much of the paper discusses the quality control of the basic station precipitation series. Although the primary aim of the development has been RCM validation, we have assessed trends in seasonal precipitation totals as well as trends in two measures of precipitation extremes (R95p, the daily precipitation amount exceeded only 5% of the time and Rx5day, the maximum 5-d precipitation total during each season). Relatively few regions across the large domain have statistically significant trends, but those that do tend to be located in the eastern two thirds of the grid, particularly over southeastern Brazil and Uruguay. Significant trends are also more evident in the DJF and MAM seasons. There is good spatial agreement between the trends in seasonal totals and trends in the extreme indices. © 2012 Royal Meteorological Society.

Descripción: This paper evaluates a present climate simulation over southern South America performed with the Meteorological Research Institute/Japanese Meteorological Agency (MRI/JMA) high resolution global model. Main patterns of low and upper-level atmospheric circulation were analysed in a 25-year simulation as well as climate means, interannual variability, trends and bias of temperature and precipitation. The model is able to reproduce the main atmospheric circulation patterns and mean surface variables, although some deficiencies were found such as an overestimation of temperature over central Argentina in most of seasons, an overestimation of austral winter precipitation over northeastern and central Argentina, an underestimation of precipitation in all the seasons over southeast of Brazil, an underestimation of the amplitude of the annual cycle temperature in some regions and an overestimation of the amplitude of the annual cycle of precipitation over mountainous areas. Model interannual variability was also assessed. In general, temperature variability is overestimated, whereas precipitation is underestimated. The spatial structure of the year-to-year variability of precipitation is correctly simulated by the model, although some patterns were misplaced. Most of regions present a cold seasonal bias reaching values of - 2 °C in some regions. It was found that precipitation biases are between 3 and - 1 mm day-1. In some regions and seasons observed and simulated temperature trends coincide, as in austral summer or spring, where the model and the observations show positive trends in most of regions. However, there is no agreement between observed and simulated precipitation trends in almost all the regions and seasons. © 2012 Royal Meteorological Society.

Descripción: This study analyses heating degree-days (HDDs) in Argentina during the period 1900-2008. Gridded temperature data provided by the University of Delaware were analysed to calculate monthly and annual cumulative HDDs. Mean, maximum and minimum values as well as the average duration of the heating season are used to characterize the mean features of the region. Spatial variations are driven by latitude and altitude. The analysis of the temporal distribution of HDDs reveals that the centre of the mean heating season varies from mid-June to mid-July. The length of the cold season grows with increasing latitude and westward with increasing altitude. In the high Andes, the heating season extends all year round. S-mode principal component analysis is used to identify sub-groups of grid points with similar temporal variability. Negative trends in annual cumulative HDDs are detected in most of the country. Linear and nonlinear trends as well as temporal statistics are examined for inter- and intra-annual variability of HDDs to discuss its potential incidence on residential use of natural gas. Seasonal increases in natural gas consumption in the country, including the effect of regional price benefits, could be now better explained not only by population growth but also by the spatial and temporal characterization of the HDD season. © 2012 Royal Meteorological Society.

Descripción: A regression approach was used to quantitatively estimate the attribution of the notable growth in the river flows of the Plata Basin during 1960-1999. The study was conducted in seven large basins that account for most of the Plata River discharge. Annual rainfall integrated over each basin and annual river flows at their closing points were used for the analysis. The contribution of rainfall changes during each of the three phases of El Niño-Southern Oscillation to total rainfall change in these basins was also calculated. The two main drivers for the generalized growth of the river flows were the increased precipitation and the decreased evaporation attributable to land use change, including deforestation of natural forest and crop switch from sugarcane and coffee trees to soybean. Other evaporation changes played a minor role. There was a north-south gradient in the respective importance of each driver, with land use change having greater weight in the northern basins and the precipitation increase in the southern ones. Thus, in the northern part of the Upper Paraná Basdespite the negative trend in precipitation there was a strong augment of the river flow caused by land use change. The contribution to the positive trend of the stream flows in the middle of the Plata Basin came from both land use change and increased precipitation. Finally, in the south, the Uruguay River flow change was basically due to the precipitation trend that was not only observed during the El Niño phase, but also during the Neutral phase. Only in the Middle Paraguay Basin was the shift to more frequent and intense El Niño events that took place in the 1970s an important factor in the contribution of precipitation to streamflow trends. © 2010 Royal Meteorological Society.

Descripción: Intradiurnal variation of arboreal pollen (AP) in Mar del Plata city is compared during three non -consecutive years of survey and described in relation to the associated weather. The daily pattern of pollen abundance has a maximum between 10:00 and 12:00 h, while a minimum occurs at 18:00 h. The first two years of survey showed homogeneous daily trends, but in 1995 the maximum and minimum concentrations were delayed because of the change in position of the collecting station. Arboreal pollen spectrum presented qualitative and quantitative changes in the three years analysed. Results indicate optimal conditions for diurnal dispersion of arboreal pollen are high temperatures and low relative humidity. Also interaction between source position and wind direction has important effects on the timing of the peaks of some pollen types.

Descripción: Rock maenetism techniques were applied to the study of the palaeosols and loess in the Chaco-Pampean plain region, Buenos Aires, Argentina; in addition, several types of non magnetic analysis were carried out: chemical analysis of ferrous and ferric, titanium and magnesium ions and x-Ray difraction. The magnetic susceptibilities of the Argentine palaeosol and loess exhibit different trends to those observed in the well known Chinese examples with which they are compared. In the Chacopampean succession the susceptibility of the loess is higher than that of the palaeosol. This can be explained by differences in the parental material imparting different magnetic properties. © 1998 Asociaciön Geolögica Argentina.

Descripción: A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951-2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with near-complete data for 1901-2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901-1950, 1951-1978 and 1979-2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

Descripción: Monthly lower stratosphere temperature anomalies in a layer centred about 70 hPa, from the MSU data set are analysed for the period 1979-1997. T-mode approach principal component analysis (PCA) is used in order to obtain the leading spatial anomaly patterns and their sequences of occurrence throughout the period under study. Five principal components (PCs) are significantly different from the spatial distribution of noisy data. The patterns given by the PC scores represent ten typical spatial anomaly patterns: five correspond to the direct mode, that is to say anomaly fields with the same sign as the PC score patterns, and five have the opposite sign. The first three PCs represent simple spatial temperature anomaly distributions, with zonal wave 0 to wave 2 wave structures. The following significant PCs, orders four and five, display a more complex spatial behaviour, with wave 3 wave structures. The first two PC's frequency distribution in time, given by the PC loadings time series, do not show noticeable changes throughout the period analysed. The remaining three PCs show changes in their frequency of occurrence that might be associated with the negative trends in the lower stratosphere temperature, as well as to the other different features observed in the real temperature anomaly time series for the grid points in the Southern Hemisphere. The latter are studied with the PCA in the S-mode approach in the companion paper (Compagnucci et al., 2001. International Journal of Climatology 21: 419-437). Copyright © 2001 Royal Meteorological Society.

Descripción: Crystal structures are presented for two members of the homologous series of 1,2-dibromo-4,5-dialkoxybenzenes, viz. those with decyloxy and hexadecyloxy substituents, namely 1,2-dibromo-4,5-bis(decyloxy)benzene, C26H44Br2O2, (II), and 1,2-dibromo-4,5-bis(hexadecyloxy)benzene, C38H68Br2O2, (III). The relative influences which halogen bonding, π- π stacking and van der Waals interactions have on these structures are analysed and the results compared with those already found for the lightest homologue, 1,2-dibromo-4,5- dimethoxybenzene, (I) [Cukiernik, Zelcer, Garland & Baggio (2008). Acta Cryst. C64, o604-o608]. The results confirm that the prevalent interactions stabilizing the structures of (II) and (III) are van der Waals contacts between the aliphatic chains. In the case of (II), weak halogen C - Br ⋯(Br - C) ′ interactions are also present and contribute to the stability of the structure. In the case of (III), van der Waals interactions between the aliphatic chains are almost exclusive, weaker C - Br ⋯ π interactions being the only additional interactions detected. The results are in line with commonly accepted models concerning trends in crystal stability along a homologous series (as measured by their melting points), but the earlier report for n = 1, and the present report for n = 10 and 16, are among the few providing single-crystal information validating the hypothesis.

Descripción: We investigated the selective predation of mixotrophic and heterotrophic flagellates (MF and HF) on different heterotrophic prokaryote phylotypes (HPP; Bacteria + Archaea) living in natural assemblages from oligotrophic Antarctic lakes. In situ prey preference was analyzed for the first time on different mixotrophic taxa (Pseudopedinella sp., Ochromonas-like cells, Chrysophyceae >5 μm). The relative abundances of seven different HPP hybridized by CARD-FISH (catalyzed reporter deposition-fluorescent in situ hybridization) in natural community were compared with the proportions of hybridized cells inside digestive vacuoles. Our results showed some general trends to selectivity over some HPP. Alphaproteobacteria and Betaproteobacteria were the most abundant groups, and strikingly, a negative selection trend was detected in most samples by all bacterivorous protists. In contrast, for Actinobacteria a positive selection trend was observed in most samples, whereas Bacteroidetes seemed to be randomly preyed upon. Interestingly, similar prey preferences were observed in all bacterivorous flagellates. Our results suggest that phylogenetic affiliation determines part of the process of prey selection by protists in these lakes. Nevertheless, other features, such as cell size, morphology and the presence of the S-layer, might also significantly contribute to prey selectivity on the HPP. © 2012 The Author 2012. Published by Oxford University Press. All rights reserved.

Descripción: Proximity effects on 1J(CH) couplings are studied from a theoretical point of view in the following systems: CH4/FH (A) and H2O/HCN (B) which form dimers by hydrogen-bond interactions. 1J(CH) couplings for different intermolecular distances are calculated for the C - H bond facing the atom bearing lone pairs. While in the former system, this coupling is increased owing to the proximity to the F atom; in the latter this coupling is decreased owing to the proximity to the O atom. These opposite trends are accompanied by slight shortening and lengthening, respectively, of the corresponding C - H bond lengths. As part of this work, measurements of 1J(CH) couplings in 9-(1,3-dioxolan-2-yl)-1,2,3,4-tetrafluorotriptycene (I) and 1-formyl-2-hydroxy-8-fluoronaphthalene (II) and 1J(NH) in o-fluorobenzamide (III), showing proximity effects as those described above are carried out. These results suggest that 1J(XH) couplings are adequate probes to distinguish two different types of X-H⋯Y hydrogen bonds. © 1994 American Chemical Society.

Descripción: Factors of soils formation, parent material, and relief in western part of Santa Cruz province (southermost Patagonia) were studied in rio de las Vueltas valley beetween Laguna del Desierto and Lago Viedma (49oS-49o30′S y a 73o W). There is great soil variability related to a strong north-west-south-east bioclimatic and geomorphic gradient. Soils were studied in a NW-SE transect, where three different sectors could be distinguished. The western area, including the Patagonian Andean Cordillera and piedmont is characterised by strong landscape variations due to glacial processes, colluvial, glacial, cineritc and glacifluvial parent materials, a udic-xeric regime and Nothofagus woodlands. The landscape of the eastern area is mainly of glacial-fluvioglacial, fluvial origin, with aeolian landforms, an and regime, grassland-shrub steppe and large flat structural plain landscape. Because of their different landscape-relief features and parent materials, both areas have different soils associations. The western area is characterized by a distrudepts, udivitrands/hapludands and haploxerolls sequence, meanwhile the eastern by an haplargides, torriortents and haplocalcides trends. In the western area, podzolisation features were recognized. In the north-western sector, Bs and E horizons were recognized, and low pH base saturation values, due to climatic conditions, indicate ongoing podzolization. Elsewhere in the south-eastern sector calcium carbonate from the surface, basic pH and total saturation are soils main features. © 2004 Asociación Geológica Argentina.

Descripción: Geochemical features and neomorphism of Chachao Formation calcareous rocks (Valanginian)-Malargüe Anticline, Mendoza. The Lower Cretaceous Chachao Formation in the Malargüe anticline area consists of wackestone, packstone, grainstone and minor mudstone rich in benthic fauna (mainly bivalves) which were deposited in a shallow carbonate ramp as previous sedimentological studies have proposed. Standard petrographic, XRD, SEM, cathodoluminiscense and trace element determinations composition of micrite and microsparite mosaic crystals were undetaken in order to characterize their original mineralogy. The SEM shows that the mud fraction is composed of a mosaic texture of subhedral to anhedral micrite and microsparite crystals, both showing similar features such as smooth (unpitted) surfaces and lack of aragonite relicts. Crystal morphology also rules out the possible presence of aragonite. These features together with the microfabric, low Sr content (average: 592 ppm) of both micrite and microsparite point to an original high-magnesium calcite composition of the muds. Geochemical data from the micrite and microsparite of the mud-supported rocks of the Chachao Formation show two contrasting trends : decreasing-upward Sr and Na concentrations and increasing-upward Mg and Mn concentrations. The loss of Sr and Na are related to mineralogical stabilization of metastable carbonate particles involving the inversion of high-magnesium calcite to low-magnesium calcite, whereas local dolomitization in the upper part of the studied sequence has formed dolomite crystals showing different stages of dissolution due to meteoric and marine water influences. © 1999 Asociación Geológica Argentina.

Descripción: Along the eastern front of the Sierra de Velasco and at the southern end of the Sierra de Ambato, western Sierras Pampeanas, have been found new evidences of Quaternary tectonic activity near La Rioja city. Observed evidences correspond to different reactivated sections of the faults that bound the mountain fronts, as well as to structures affecting the Quaternary deposits on the piedmont. The bounding faults of the Sierra de Velasco Oriental-front exhibit a NNE trend and WNW dip, while structures at the southernmost Ambato range are characterized by NE trend and NW dip. The neotectonic faults of the El Carrizal block are the result of the interference of both structural trends, resulting in a sector with higher structural complexity. The here described deformation show the persistence of a compressive regime during the Quaternary, with eastern to southeastern verging reverse faults. It is considering that these faults are driving the current uplift of the mountain ranges and constitute potential earthquake sources.

Descripción: We tested the applicability of Allen ' s rule in 47 species and 32 unnamed forms (populations that are probably good species or undefined taxa within a superspecies or species group) of the South American subterranean Hystricomorph rodents of the genus Ctenomys (tuco-tucos) (Rodentia: Ctenomyidae) by analyzing tail length in relation with head and body length, and body mass. Tail length allometry was analyzed by Reduced Major Axis regression while the possible correlation of relative tail length with temperature, precipitation and evapotranspiration variables was explored through Simultaneous Autoregression to account for spatial autocorrelations. Our results indicate that tuco-tucos do not follow Allen ' s rule but its converse, tail proportion relative to body mass increasing with latitude while body size decreases in the same direction (the trend is similar for tail length relative to head and body length but not statistically significant). Regarding climatic variables, the main predictors of relative tail length were temperature and evapotranspiration variables with trends confirming the positive (non-Allenian) correlation of relative tail length with latitude. We conclude that tuco-tucos, being almost fully subterranean, thermoregulate behaviorally by maintaining constant temperatures within their burrows independent of geographic location. The former confirms previous results that indicated that Ctenomys follows the converse to Bergmann ' s rule. Relative tail length variation would be a result of simple allometric growth. © 2011 by Walter de Gruyter.

Descripción: Although there have been many ecological field studies on the key components of planktonic food webs, there are still gaps in knowledge on some groups, environments and seasons. This is the first report on the spatial distribution of the density and biomass of almost all the taxonomic groups and size fractions of protozooplankton across a cold-temperate shelf during winter. Twenty-eight stations (two or three depths) were sampled on four cross-shelf transects in Patagonian waters (south-western Atlantic; 47-55°S, 60-69°W) during September 2006. Loricate ciliates, radiolarians and foraminiferans showed the lowest densities, and were distributed mainly in coastal, slope or the whole shelf waters, respectively. The density and biomass of aloricate ciliates and heterotrophic nanoflagellates and dinoflagellates were low and homogeneous both vertically and across the shelf south of 51°S, but peaked in the upper 40 m in offshore waters at 47°S. Microplanktonic aloricate ciliates, which represented 53% of the total protozooplankton biomass, reached values as high as 16 μg CL-1 on the last transect. Consequently, both protozooplankton biomass and its ratio to chlorophyll a concentration were significantly higher in the northern offshore waters. These trends were linked to higher subsurface temperature and chlorophyll a concentration, and lower copepod nauplii biomass. Our results probably reflect changes in both the availability of food resources and predators and the physical structure of the water column, which are a consequence of the different environmental conditions that coexist over the large latitudinal and longitudinal gradients covered during late winter. © The Author 2010.

Descripción: Background: Detailed analysis of the dynamic interactions among biological, environmental, social, and economic factors that favour the spread of certain diseases is extremely useful for designing effective control strategies. Diseases like tuberculosis that kills somebody every 15 seconds in the world, require methods that take into account the disease dynamics to design truly efficient control and surveillance strategies. The usual and well established statistical approaches provide insights into the cause-effect relationships that favour disease transmission but they only estimate risk areas, spatial or temporal trends. Here we introduce a novel approach that allows figuring out the dynamical behaviour of the disease spreading. This information can subsequently be used to validate mathematical models of the dissemination process from which the underlying mechanisms that are responsible for this spreading could be inferred. Methodology/Principal Findings: The method presented here is based on the analysis of the spread of tuberculosis in a Brazilian endemic city during five consecutive years. The detailed analysis of the spatio-temporal correlation of the yearly geo-referenced data, using different characteristic times of the disease evolution, allowed us to trace the temporal path of the aetiological agent, to locate the sources of infection, and to characterize the dynamics of disease spreading. Consequently, the method also allowed for the identification of socio-economic factors that influence the process. Conclusions/Significance: The information obtained can contribute to more effective budget allocation, drug distribution and recruitment of human skilled resources, as well as guiding the design of vaccination programs. We propose that this novel strategy can also be applied to the evaluation of other diseases as well as other social processes. © 2010 Zorzenon dos Santos et al.

Descripción: A database of daily extreme temperature was created for as many stations as possible for Uruguay, as far back as possible. This is the first attempt to gather all the different data sources together, perform a quality control and homogeneity assessment. We work with seven stations; it should be taken into account that Uruguay is a small country (around 177 000 km2) and this represents most of the available data. There are three old series with starting dates in 1930, and four that start around 1950. From this database, a set of four extreme temperature indices was constructed for the oldest five stations, warm days (TX90), cold days (TX10), warm nights (TN90) and cold nights (TN10). The index TN10 shows the largest significant negative trend for the period 1960-2002, while TN90 shows a positive but not significant trend for this period indicating a strong warming of nighttime temperature. A spectral analysis was performed using the multi taper methods (MTM) to the de-trended annual, summer Dec-Feb (DJF) and winter Jun-Aug (JJA) indices time-series. This analysis shows that on inter-annual timescales, the most significant range of frequencies is from 2 to 2.5 years and from 3 to 6 years. Low frequencies of variability were detected when the MTM was applied to de-trended smoothed annual time-series, around the range of frequencies of 15-25 years for almost all the indices analysed. Links with global sea surface temperature (SST) were studied for two stations (Paysandu and Rocha), and it was found that the indices showed largest correlations with SST anomalies in the Pacific Ocean. We detected changes in the response of the TN10 index for Rocha station when the series was split up into two different periods (1942-1976 and 1977-2005). Copyright © 2007 Royal Meteorological Society.