Una metodologia para la estimación local de la velocidad del viento mediante un modelo numérico

Se utiliza un modelo numérico unidimensional de Ia capa Iímite atmosférica, con clausura turbulenta de segundo orden, ρara estimar velocidades medias del viento cerca de superficie en lugares donde no existen observaciones disponibles. El modelo emplea como condiciones de contorno datos sinópticos de temperatura, viento geostrófico en niveles standard obtenidos de cartas sinópticas y condiciones locales de rugosidad superficial. El método es verificado por comparación con cuatro series de velocidades de viento, medidas a 15, 60 y 90 metros sobre el nivel de superficie en Ia localidad de Pampa del Castillo (Chubut), durante Ios meses de abril, agosto y octubre de 1980 y enero de 1981. Los errores relativos en Ias velocidades medias computadas en cada uno de Ios cuatro meses y en cualquiera de Ios tres niveles son del orden del 5 por ciento. Los errores cuadráticos medios relativos a Ia varianza y al valor medio son del orden de 0,24 y 0,19 respectivamente en el caso de velocidades medias diarias, y del orden de 0,17 y 0,11 en el caso de velocidades medias semanales. Los resultados numéricos muestran que Ia metodología puede ser útil para obtener, a un costo computacional razonable series cortas de velocidades medias diarias y semanales, y también, para una rápida estimación de Ia velocidad media del viento para períodos largos en lugares que no disponen de observaciones.A one-dimensional atmospheric boundary Iayer model, with a second-order turbulent closure, is used to estimate near surface mean wind velocities in Iocations where no observation is available. Synoptic data, such as tempcrature, geostrophic wind at standard Ievels obtained from synoptic charts, are used as boundary conditions together with local surface roughness parameterization. As methodology verification simulated wind velocity series are compared with observations made at 15, 60 and 90 meters above the ground at Pampa del Castillo (Chubut) Iocation, durlng april, august and october 1980, and january 1981. Relative errors in computed mean veIocities, in each of the four months and at any of the three Ievels are of order of 5 percent. Mean square errors reíative to the variance and to the mean velocity, are about 0,24 and 0,19 respectively in the case of daily mean velocity series, and about 0,17 and 0,11 in the case of weekly mean velocity series. Numerical results show that the methodology can be useful to obtain, at a reasonable computational cost, short series of daily or weekly mean wind velocities, and also, for quick assessment of long-range mean wind velocities at Iocations where observations are not available.Asociación Argentina de Geofísicos y Geodesta

Un modelo numérico de difusión de contaminantes

Se propone la simulación numérica de un proceso de difusión turbulenta desde un emisor lineal de contaminantes. Las ecuaciones hidrodinámicas acopladas con la ecuación de conservación del contaminante y simplificadas con la aproximación de Boussinesq son integradas por diferencias finitas. Se retiene el efecto de la perturbación de la presión sobre el movimiento. Los resultados muestran, para el caso de estabilidad neutral campos estadísticamente estacionarios de la concentración y de las variables hidrodinámicas, los cuales satisfacen las descripciones generales de modelos más simples.A numerical simulation of a turbulent diffusion process from a linear source of pollutant is proposed. The hydrodynamical equations, coupled with the pollutant conservation one, are integrated by a finite difference method. Boussinesq approximation is made and the pressure perturbation effect on momentum equation is preserved. Results, show for the neutral stability case, statically stationary fields both for hydrodynamics variables and pollutant. Agreement with less sophisticated model is observed.Asociación Argentina de Geofísicos y Geodesta

Statistical downscaling estimation of recent rainfall trends in the eastern slope of the Andes mountain range in Argentina

Statistical models for rainfall downscaling based on multiple linear regression techniques have been developed and tested in the Andean Region of west Argentina, an extended mountainous region where three different rain regimes predominate and rainfall has great spatial and temporal variability. The verification procedure was focused on the model's ability to reproduce observed rainfall trends in recent decades. In the northwest of Argentina, domain of the tropical summer rain regime, the monthly rainfall variance accounted for by downscaling models was 77% on average and models reproduced satisfactorily the negative linear trend observed in the last two decades of the past century. In the arid central-west Argentina, a region of rapid transition between two different rain regimes, model performance was rather poor (an average of 50% of explained variance), even so models were able to capture outstanding differences in the linear trend between the northern and southern sectors of the region. In the southwest of Argentina, domain of the mid-latitude winter rain regime, the monthly variance accounted for by downscaling models was 71% on average and models were capable to reproduce a singular change in the onset of the rainy season that occurred during the 1990s. The results achieved demonstrate that it is feasible to establish significant and useful statistical relationships between atmospheric variables and rainfall at monthly and river basin scales, even for a topographically complex region like western Argentina.Fil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Simulation capability of tropical and extratropical seasonal climate anomalies over South America

An ensemble of 20 extended integrations of the atmospheric model CSIRO Mark 2, forced with the sea surface temperature observed during the 1986–1998 period, was performed to analyze the simulation capability of seasonal climate anomalies over South America and adjacent oceanic areas. Variations of the simulation skill within the region and during the experimental period were assessed through standard statistical measures and compared to the signal-to-noise ratio distribution. Before the skill assessment, model systematic errors were thoroughly evaluated. The results confirm that the simulation skill is very high in tropical oceanic areas, and decreases rapidly towards middle and high latitudes. Model performance at mid and high atmospheric levels is substantially better than at low levels. Relatively high simulation capability was found over the Pacific Ocean between the equator and the Antarctic coast, which is coherent with the presence of three relative maximums in the signal-to-noise ratio, similar to the increase of the forced variance found by several authors over much of the Pacific–North American pattern region. Rainfall rate and second-order moments associated with the cyclonic activity and the meridional eddy fluxes of heat and humidity are better simulated in a narrow strip parallel to the SPCZ and extending further southeast into mid latitudes of the continent. The simulation skill noticeably improves during the warm and cold ENSO phases, in correspondence with an intensification of the signal-to-noise ratio, and useful rainfall anomaly simulations can be obtained over the Amazonas and Rio de la Plata river basins.Fil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin

Climate in the Monte Desert: Past trends, present conditions, and future projections

This paper documents the main features of climate and climate variability across the Monte Desert for the Last Glacial Maximum, the Glacial-Interglacial transition, and the Holocene on the basis of proxy records and for the 20th century using instrumental observations. The climate in the Monte is determined by interactions between regional physiography and atmospheric circulation in the 25-45°S sectors of South America. Although arid and semi-arid conditions prevail across the Monte, its large latitudinal extent and complex topography introduce many particularities at local scales. Paleoclimatic records and model simulations of past climates suggest significant variations in the atmospheric circulation, temperature and rainfall patterns since the Last Glacial Maximum. High-resolution proxy records east of the Andes support the existence of complex climatic patterns with similar temperature changes across the whole region but opposite precipitation variations between subtropical and mid-latitude sectors in the Monte during the past millennium. The present-day climate is depicted in terms of the space and time variability of the near-surface temperature, rainfall and tropospheric wind patterns. Uneven temperature trends over the Monte were recorded for two separate (1920-44 and 1977-2001) global warming periods in the 20th century. Additional warming evidence in the region is provided by extreme temperature records. The non-homogeneous regional pattern of precipitation shows a positive long-term increase between 30 and 40°S during the interval 1985-2001. Ensemble of climate experiments accomplished with general circulation models provide the most likely changes in temperature and rainfall to occur by the end of this century in relation to present climate. Temperature increases, larger in summer than in winter, will be concurrent with more abundant precipitations in summer, but almost no changes or even small reductions in winter across the Monte.Fil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

A reply to McMahon et al.(2008)

Recently, McMahon et al. (2008) criticized our article concerning the impacts of climate variability on the reproductive parameters of southern elephant seals (Vergani et al., 2008). We characterized El Niño–Southern Oscillation (ENSO) climate anomalies in the periphery of Antarctica using reanalysed global atmospheric data from Kalnay et al. (1996) encompassing over 40 years of observations. We considered existing evidence for ENSO signals in delineated regions of Antarctica and the current understanding of propagation mechanisms from the source region in the tropical Pacific Ocean to high latitudes of the Southern Hemisphere.Fil: Vergani, Daniel Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Centro de Estudios Territoriales; ArgentinaFil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Advances in the climatic forecast of rainfall anomalies in the Pampa Region

Los modelos globales de la circulación general de la atmósfera (MCGA) son capaces de simular anomalías climáticas estadísticamente significativas de escala estacional o mayor, asociadas con anomalías en la temperatura de la superficie del mar. Los MCGA pueden estimar efectivamente el signo y la probabilidad de tales anomalías climáticas cuando su extensión es varias veces mayor que la resolución espacial del modelo. En este trabajo se presentan algunos avances en la estimación de las anomalías de la lluvia en 22 localidades de la Región Pampeana Argentina mediante downscaling estadístico de la información producida por un ensamble de veinte simulaciones con el MCGA CSIRO-9, prescribiendo la temperatura de la superficie del mar de acuerdo con los valores diarios observados en el período 1987-1998. El downscaling estadístico de la lluvia produjo una mayor correlación con las observaciones locales que los datos de lluvia del MCGA interpolados sobre cada sitio. Los resultados de un Análisis de las Componentes Principales aplicado a los datos observados y estimados indican que este método de downscaling permite discernir áreas con diferente comportamiento de la lluvia dentro de la región de estudio.Atmospheric general circulation models (AGCM) are able to simulate statistically significant climate anomalies of seasonal or larger time-scales, associated with anomalies in the sea surface temperature. AGCMs can effectively estimate the sign and probability of such climate anomalies whenever their extent is several times greater than the spatial resolution of the model. Some progress attained in the estimation of rainfall anomalies in 22 sites of the Pampa Region, Argentina, by means of statistical downscaling of the output from an AGCM are presented in this work. Downscaling models were based in the multiple lineal regression method. Climatic anomalies of the atmospheric independent variables required in the rainfall downscaling procedure were obtained from the ensemble average of twenty simulations carried out with the AGCM CSIRO-9, prescribing the sea surface temperature according to observed daily values in the period 1987-1998. The statistical downscaling of rainfall produced greater correlation with local observation than the AGCM rainfall data interpolated over each location. The results of a Principal Component Analysis applied to the observed and estimated data reveal that this downscaling approach is able to distinguish areas with different rainfall behavior within the study region.Fil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Brandizi, Laura Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Lopez, Monica Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Atmospheric and fuel conditions related to the Puerto Madryn Fire of 21 January, 1994

The atmospheric and fuel conditions that led to the case of extreme fire behaviour registered in Puerto Madryn in north-eastern Patagonia, Argentina, on 21 January 1994 were analysed in this study. The analyses included surface and upper-air meteorological conditions, fuel composition and load, and morphometry of the burnt area. When the fire occurred the total fuel load was 16 688 ± 2 611 kg of dry matter per hectare, with fine fuel representing 66% of the total fuel load. At the time of the major fire run, the air temperature reached 32°C and relative humidity decreased to 13%. The fuel load and its high proportion of fine fuels, the extreme temperatures, the low relative humidity, and the changes in wind directions which resulted from the conjunction of synoptic and local-scale phenomena, enhanced the development of a large convection column which favoured the interaction of surface and upper-air winds. As in similar cases reported for other ecosystems, the combination of these phenomena led to this case of extreme fire behaviour. It is intended that this analysis will contribute to the future development of fire alert systems for the region and to the worldwide knowledge of extreme fire behaviour in different scenarios.Fil: Dentoni, M. C.. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Defossé, Guillermo Emilio. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: del Valle, Hector Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin

Scenarios of Future Climate and Land-Management Effects on Carbon Stocks in Northern Patagonian Shrublands

We analyzed the possible effects of grazing management and future climate change on carbon (C) stocks in soils of northern Patagonian shrublands. To this aim, we coupled the outputs of three (HadCM3, CSIRO Mk2, and CCSR/NIES) global climate models to the CENTURY (v5.3) model of terrestrial C balance. The CENTURY model was initialized with long-term field data on local biome physiognomy, seasonal phenologic trends, and prevailing land-management systems and was validated with recent sequences of 1-km Normalized Difference Vegetation Index (MODIS-Terra) images and soil C data. In the tested scenarios, the predicted climate changes would result in increased total C in soil organic matter (SOMTC). Maximum SOMTC under changed climate forcing would not differ significantly from that expected under baseline conditions (8 kg m−2). A decrease in grazing intensity would result in SOMTC increases of 11% to 12% even if climate changes did not occur. Climate change would account for SOMTC increases of 5% to 6%.Fil: Carrera, Analía Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Ares, Jorge Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Thurner, Stephanie. Universitat Technical Zu Munich; AlemaniaFil: Bertiller, Mónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Apariencia uniforme en los mejillinares intermareales del Atlántico Sudoccidental: ¿El stress ambiental es suficiente explicación?

Las comunidades rocosas intermareales del Atlántico Sudoccidental (ASO) tienen una apariencia uniforme, siendo dominadas por densas extensiones de tres bivalvos Brachidontes rodriguezii, Perumytilus purpuratus y Mytilus sp. Éstas se reemplazan unas a otras a lo largo de un extenso gradiente latitudinal (34°S a 54°S). Esta uniformidad puede atribuirse a varios factores: (1) factores ambientales (stress por desecación) que afectan a toda la comunidad caracterizada por la carencia de depredadores tope, (2) la historia ambiental reciente de las costas que afectaron la distribución geográfica de las especies. En este estudio analizamos la primera hipótesis, estudiando la distribución y composición de las comunidades a nivel regional. Para tal fin, (1) se utilizó la información de abundancia de las 21 localidades S, (2) se construyeron perfiles latitudinales de las variables ambientales: temperatura superficial del mar, amplitud de mareas, precipitaciones, temperatura atmosférica y tasa de evapotranspiración, y (3) se recopiló toda la información disponible y críptica sobre la composición de las comunidades intermareales. Todas las variables ambientales estuvieron linealmente correlacionadas con la latitud, a excepción de la tasa de evapotranspiración. Teniendo en cuenta esta última variable, los resultados permitieron dividir las 21 localidades en 4 grupos: (1) templado cálida, dominada por B. rodriguezii; Patagonia (2) norte, donde B. rodriguezzi es reemplazado por P. purpuratus; (3) centro, dominado por P. purpuratus; y (4) sur, dominado por Mytilus sp. Las localidades del norte y centro de Patagonia presentaron valores máximos de stress por desecación, pero el reemplazo latitudinal de las especies estuvo relacionado con cambios en la temperatura superficial del agua. En conclusión, la apariencia uniforme de las comunidades intermareales debido a la falta de invertebrados depredadores móviles de los mejillines no estaría relacionada con las variaciones registradas en las tasas de desecación y podría ser consecuencia de la historia ambiental reciente del ASO.Fil: Adami, Mariana Laura. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Schwindt, Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; ArgentinaFil: Tablado, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Calcagno, Javier Ángel. Universidad Maimónides. Área de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Labraga, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; ArgentinaFil: Orensanz, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaIX Jornadas Nacionales de Ciencias del Mar y XVII Coloquio de OceanografíaUshuaiaArgentinaCentro Austral de Investigaciones CientíficasUniversidad Nacional de Tierra del Fueg