Validación de las alturas geopotenciales de 1000 hPa obtenidas del modelo de diagnóstico del Servicio Meteorológico Nacional

Se realiza un análisis espacial objetivo de datos diarios de alturas geopotenciales del nivel de 1000 hPa sobre la región del Cono Sur, calculados a partir del modelo de diagnóstico del Servicio Meteorológico Nacional Argentino, correspondientes a los meses de Enero y Julio del período 1990-95; a fin de arribar a una evaluación de su confiabilidad en estudios con escala de tiempo superior a la sinóptica. Para ello se emplea el Análisis de Componentes Principales no-rotadas con matriz de entrada en modo-T, técnica que se repite para diferentes enrejados; comparando estos resultados con los obtenidos previamente por Compagnucci y Salles (1996), bajo la misma metodología, para un período distinto y con datos observados desde estaciones meteorológicas de superficie. El modelo ajusta razonablemente la configuración de los sistemas que se presentan en el área, mostrando asimismo la influencia del relieve. Sin embargo, la inclusión de la región oceánica en el análisis podría estar forzando una estructura similar a la del flujo básico, perdiéndose además la variabilidad estacional de los campos resultantes. Este comportamiento se vería reflejado en la mayor varianza explicada por el campo medio al incluir observaciones marítimas, con lo cual, las inferencias estadísticas extraídas a partir de datos del modelo deberían contemplar este hecho, que tendería a subestimar la varianza explicada por perturbaciones de mayor frecuencia.An objective spatial analysis has been performed from 1000 hPa-geopotential heights daily data obtained from the Meteorological National Service diagnostic model output for the southern cone region and correspond to the months of January and July from the period 1990-95. It aims to evaluate the diagnostic model reliability in time scales longer than synoptic scale for future weather researches. Unrotated Principal Component Analysis with T-mode input matrix has been applied to different gridpoint distributions in order to compare the results to those previously obtained by Compagnucci and Salles (1996) with the same methodology applied to observed data from surface meteorological stations though for a different period. The model reasonably fits the synoptic systems features present over the area. However, the inclusion of the oceanic region in the analysis could possibly force to a structure similar to of the resulting fields. This behavior can be observed in the major variance explained by the mean field when including sea observations. For this reason, eventual statistics inferences drawn from the diagnostic model output ought to take into consideration this fact giving that it would tend to underestimate the concomitant variance of higher frequency perturbations.Asociación Argentina de Geofísicos y Geodesta

Comparison between circulation patterns associated to frost events in the humid pampa in climatic settings related with the experiments CMIP3 and CMIP5 of the GFDL model

El propósito de este estudio es investigar los cambios en la circulación atmosférica asociados a eventos de heladas en la Pampa Húmeda (PH) en el clima futuro para los escenarios más críticos proyectados por el modelo acoplado oceano-atmósfera GFDL. Se emplea el modelo GFDL en sus dos versiones (GFDL-CM2 para el CMIP3 y GFDL-CM3 para el CMIP5). Se analiza la capacidad del modelo para simular los cinco eventos extremos más fríos en el clima presente (1961-1990), respecto de los obtenidos en el reanálisis del NCEP/NCAR. Luego se comparan las simulaciones del clima futuro (2081-2100) con las del presente. En el experimento CMIP3 del clima presente el modelo muestra una mayor penetración de la isoterma de 0°C en 850 hPa, con anomalías de temperatura negativas más intensas que las del NCEP. El anticiclón pos frontal se observa más extendido meridionalmente sobre el continente, con valores de anomalías similares principalmente en la Pampa Húmeda. El gradiente de presión entre la alta y la baja corriente abajo, provoca un flujo de aire frio del sur más intenso en 850 hPa que en el reanálisis, propiciando heladas del tipo advectivas en la región de estudio. En el clima futuro el modelo proyecta una menor incursión de la isoterma de 0°C y con anomalías negativas de temperatura más pequeñas. El máximo del anticiclón en el futuro se localiza más al norte que en el presente, propiciando heladas del tipo radiativas. En el campo de altura, el jet subtropical se presenta más zonal y con intensidades ligeramente mayores que en las simulaciones del clima presente. Para el experimento CMIP5 en el clima presente el modelo logra simular la incursión de la isoterma de 0°C, pero la anomalía de temperatura es mayor que en el reanálisis. El campo de presión presenta similares características que en el experimento de CMIP3, pero con anomalías más intensas al sur del continente. En el escenario futuro el modelo proyecta la incursión de la isoterma de 0°C, así como la anomalía negativa de temperatura, similares al presente. El anticiclón pos frontal se localiza más al norte, sobrestimando tanto su valor así como su anomalía en la PH. El campo de viento no muestra diferencias respecto del presente. En suma, comparando los dos experimentos, el de CMIP3 en el futuro muestra importantes cambios respecto al presente, lo que no ocurre en el CMIP5. Esos cambios se ven principalmente en el campo de presión, donde para el CMIP3 (CMIP5) las heladas tipo radiativas (advectivas) serían las favorecidas en la Pampa Húmeda debido a la posición del anticiclónThe purpose of this study is to investigate the change in the atmospheric circulation associated with frost events in the Wet Pampa (WP) in the future climate for the most critical scenarios projected by the GFDL oceanatmosphere coupled model. Two versions of the GFDL model are used, the GFDL-CM2 for CMIP3 and GFDL-CM3 for CMIP5. We analyze the model capability to simulate the five most extreme cold events in the present climate (1961-1990), with respect to those obtained with the NCEP/NCAR Reanalysis. Then, we compare the future climate simulations (2081-2100) with the model simulation for the present climate. For the present climate the CMIP3 experiment presents more penetration of the 0°C isotherm in 850 hPa, intensifying the negative temperature anomalies in comparison to the reanalysis. The postfrontal anticyclone is more meridionally extended over the continent, with similar anomalies to those of the reanalysis, mainly over WP. The gradient between the high pressure and the low pressure downwind creates a more intense southerly cold airflow at 850 hPa than the reanalysis, giving place to advective frosts in the studied region. For the future climate, the model projects less penetration of the 0°C isotherm and less intense negative temperature anomalies. The anticyclone maximum is located further north than in the present climate, propitiating radiative frosts. In the upper levels, the subtropical jet shows a more zonally layout and slightly higher intensity than in the present climate simulations. For the present climate the CMIP5 experiment simulates well the incursion of the 0°C isotherm, although with a more intense temperature anomaly in comparison to the reanalysis. The pressure field presents similar characteristics to those shown in the CMIP3 experiment, but with larger anomalies in the southern part of the continent. For the future scenario, the model projects the 0°C isotherm incursion as well as the negative temperature anomalies similar to the present. The post frontal anticyclone is located further north, overestimating its value and the anomaly over WP. The wind field is similar to the present simulation. Summarizing the results of both experiments, the future projections with CMIP3 show significant changes with respect to the present, which is not the case with the CMIP5 experiment. These changes are mainly reflected in the pressure field, in which the position of the anticyclone in CMIP3 (CMIP5) would favor radiative (advective) frosts over WP.Fil: Muller, Gabriela Viviana. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Rabelo Da Rocha Repinaldo, Cintia. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Araneo, Diego Christian. 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; ArgentinaFil: Andrade, Kelen. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; Brasi

Geo-climatic hazards in the eastern subtropical Andes: Distribution, Climate Drivers and Trends

Detecting and understanding historical changes in the frequency of geo-climatic hazards (G-CHs) is crucial for the quantification of current hazards and project them into the future. Here we focus in the eastern subtropical Andes (32-33° S), using meteorological data and a century-long inventory of 553 G-CHs triggered by rainfall or snowfall. We first analyse their spatio-temporal distributions and the role of climate variability on the year-to-year changes in the number of days per season with G-CHs. Precipitation is positively correlated with the number of G-CHs across the region and year-round; mean temperature is negatively correlated with snowfall-driven hazards in the western (higher) half of the study region during winter and with rainfall-driven hazards in the eastern zone during summer. The trends of the G-CHs frequency since the mid-20th century were calculated taking cautions for their non-systematic monitoring. The G-CHs series for the different triggers, zones and seasons were generally stationary. Nonetheless, there is a small positive trend in rainfall-driven G-CHs in the eastern zone during summer congruent with a rainfall increase there. We also found a decrease in snowfall-driven G-CHs in the western zone since the late 1990?s onwards, most likely due to a reduction in winter precipitation rather than to an increase in temperature.Fil: Vergara Dal Pont, Iván Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales; ArgentinaFil: Moreiras, Stella Maris. 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; ArgentinaFil: Araneo, Diego Christian. 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; ArgentinaFil: Garreaud, René. Universidad de Chile; Chile. Centro de Ciencia del Clima y la Resiliencia; Chil

Seasonal moisture sources and the isotopic composition of precipitation, rivers, and carbonates across the Andes at 32º-35.5°S

Constraining the influence of different moisture sources across the flanks of mountain ranges is important for understanding tectonic, geomorphic, and paleoclimate problems at geologic timescales, as well as evaluating climate change and water resources on human time scales. The stable isotope compositions of stream waters and precipitation are an ideal tool for this task. This study reports the results of a 2 year monthly precipitation sampling campaign on the eastern flank of the Andes in the Mendoza Province of Argentina, which began in September 2008. A total of 104 precipitation samples spanning some 2500 m of relief from nine sites were analyzed for δD and δ18O. In addition, 81 samples from Andean rivers collected on both sides of the range in 2002 and 2007 were analyzed. We employ a Rayleigh isotope fractionation modeling approach to explore spatial and temporal variations in precipitation and river water compositions. The results indicate that precipitation on the eastern slopes of the Andes at ~33°S, at elevations above 2 km, is largely derived from a westerly, Pacific-source component and a mixture of easterly and westerly sources below 2 km. Further south at ~35°S, river water compositions exhibit a strong winter influence. At 33°S, rivers have an isotopic minimum of ~ −18? across the core of the range, which has an average elevation of 4000 m, and are topographically offset from similar isotopic values of precipitation by +1000 m. Comparison of precipitation and river water data with temperature-corrected δ18O estimates from pedogenic carbonates illustrates that carbonates capture the range of variability observed in modern precipitation and Rayleigh fractionation models.Fil: Hoke, Gregory D.. Syracuse University. Department of Earth Sciences; Estados UnidosFil: Aranibar, Julieta Nelida. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Viale, Maximiliano. Universidad de Chile. Departamento de Geofísica. Facultad de Ciencias Físicas y Matemáticas; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Araneo, Diego Christian. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Llano, Carina. Museo de Historia Natural de San Rafael. Departamento de Antropología; Argentin

Tropospheric circulation features associated with interannual streamflow variability of the Tecka - Gualjaina river in Argentina

La cuenca del río Tecka - Gualjaina se localiza al Noroeste de la provincia de Chubut, Argentina y desarrolla una superficie de 5.318 km2. El trabajo explora los forzantes del sistema atmósfera-océano asociados a la variabilidad interanual del caudal para la temporada de máximo caudal (de junio a noviembre), que representa el 80% del total anual, y de mínimo caudal (de diciembre a mayo). El balance hídrico de la cuenca arrojó condiciones de aridez, por lo que el comportamiento temporal del caudal depende del de la precipitación. En el registro disponible 1956-2013 la serie de máximo caudal presentó tendencia negativa, con un cambio de régimen en las anomalías de caudal a comienzos de los 80, pasando de un predominio positivo antes a otro negativo después. La serie de mínimo caudal mostró ser más estacionaria, sin tendencia significativa. Los ciclos dominantes en ambas series temporales sólo se observaron en la alta frecuencia interanual (~ 2 años y ~ 4-5 años). Las teleconexiones y forzantes asociados a las series de caudal se analizaron para el período 1979-2013 mediante el reanálisis del ERA-Interim. Las variaciones interanuales del caudal máximo estuvieron asociadas a teleconexión troposférica de baja frecuencia (interanual) simétrica respecto del Ecuador, posiblemente asociada a variaciones en la convección tropical entre aproximadamente 10oN-10oS y 150oE-180oE, inducidas por variaciones de temperatura superficial del mar en el Pacífico occidental ecuatorial (entre 180oO-150oO). La teleconexión afectó la posición e intensidad de las corrientes en chorro subtropical y polar, alterando la trayectoria de sistemas baroclínicos invernales que precipitan en la región. Las variaciones interanuales del mínimo caudal estuvieron asociadas a una variabilidad de altas latitudes simétricamente anular, modulada por un tren de onda 3 en latitudes medias sobre el Pacífico Sur y el Atlántico Sur. Estas características pudieron haber favorecido cambios dinámicos en el transporte de humedad dando lugar a cambios en la precipitación hacia el centro-oeste y sur de la Patagonia, afectando la cuenca del río Tecka-Gualjaina. Los resultados muestran que al menos en el período 1979-2013, el río Tecka-Gualjaina tuvo como forzante principal teleconexiones trópico-extratrópico asociadas a variaciones en el calentamiento de las temperaturas de la superficie del mar del Pacífico central ecuatorial, en parte debido a la actividad de El Niño - Oscilación del Sur (ENOS).The basin of the Tecka-Gualjaina River is located in the northwest of the Chubut Province, extended over an area of 5,318 km2. The paper explores the influence of the atmosphere-ocean system on the interannual streamflow variability for the season of maximum streamflow (from June to November), which represents 80% of the annual streamflow, and of minimum streamflow (from December to May). The Hydric balance yielded dryness conditions, for which the temporal behavior of the streamflow depends on precipitation. The maximum streamflow series showed negative trend in the full available record 1956-2013, with a change in the regime of streamflow anomalies by the beginning of the 80s, evolving from a positive predominance before to a negative one after. The minimum streamflow series was more stationary, without significant trend. The dominant cycles in both time series are only observed in the interannual high frequency (~ 2 years and ~ 4-5 years). Teleconnections and forcing associated to the streamflow time series were analyzed in the period 1979-2013 using ERA-Interim reanalysis. The year-to-year variations of maximum streamflow time series were associated with low frequency (interannual) tropospheric teleconnection, symmetric about the equator, possibly associated with variations of tropical convection between about 10o N-10o S and 150o E -180o E, induced by variations of sea surface temperature in the equatorial western Pacific (180o W-150o W). The teleconnection affected the position and intensity of the subtropical and polar jets, altering the trajectory of winter baroclinic systems that precipitate in the region. The year-to-year variations of maximum streamflow time series were associated with a high latitude annular mode-like variability, modulated by a wave-3 train at mid-latitudes over the South Pacific and South Atlantic. These features might have favored dynamic changes in the extratropical moisture transport leading to changes in precipitation towards the mid-west and southern Patagonia, affecting the Tecka-Gualjaina River basin. The results showed that at least between 1979 and 2013, the Tecka-Gualjaina River streamflow variability had tropic-extratropical teleconnections as a main forcing, associated with variations in the warming of sea surface temperatures of the equatorial central Pacific, being partly due to ENSO activity.Facultad de Ciencias Astronómicas y Geofísica

Comparison between circulation patterns associated to frost events in the humid pampa in climatic settings related with the experiments CMIP3 and CMIP5 of the GFDL model

El propósito de este estudio es investigar los cambios en la circulación atmosférica asociados a eventos de heladas en la Pampa Húmeda (PH) en el clima futuro para los escenarios más críticos proyectados por el modelo acoplado oceano-atmósfera GFDL. Se emplea el modelo GFDL en sus dos versiones (GFDL-CM2 para el CMIP3 y GFDL-CM3 para el CMIP5). Se analiza la capacidad del modelo para simular los cinco eventos extremos más fríos en el clima presente (1961-1990), respecto de los obtenidos en el reanálisis del NCEP/NCAR. Luego se comparan las simulaciones del clima futuro (2081-2100) con las del presente. En el experimento CMIP3 del clima presente el modelo muestra una mayor penetración de la isoterma de 0°C en 850 hPa, con anomalías de temperatura negativas más intensas que las del NCEP. El anticiclón pos frontal se observa más extendido meridionalmente sobre el continente, con valores de anomalías similares principalmente en la Pampa Húmeda. El gradiente de presión entre la alta y la baja corriente abajo, provoca un flujo de aire frio del sur más intenso en 850 hPa que en el reanálisis, propiciando heladas del tipo advectivas en la región de estudio. En el clima futuro el modelo proyecta una menor incursión de la isoterma de 0°C y con anomalías negativas de temperatura más pequeñas. El máximo del anticiclón en el futuro se localiza más al norte que en el presente, propiciando heladas del tipo radiativas. En el campo de altura, el jet subtropical se presenta más zonal y con intensidades ligeramente mayores que en las simulaciones del clima presente. Para el experimento CMIP5 en el clima presente el modelo logra simular la incursión de la isoterma de 0°C, pero la anomalía de temperatura es mayor que en el reanálisis. El campo de presión presenta similares características que en el experimento de CMIP3, pero con anomalías más intensas al sur del continente. En el escenario futuro el modelo proyecta la incursión de la isoterma de 0°C, así como la anomalía negativa de temperatura, similares al presente. El anticiclón pos frontal se localiza más al norte, sobrestimando tanto su valor así como su anomalía en la PH. El campo de viento no muestra diferencias respecto del presente. En suma, comparando los dos experimentos, el de CMIP3 en el futuro muestra importantes cambios respecto al presente, lo que no ocurre en el CMIP5. Esos cambios se ven principalmente en el campo de presión, donde para el CMIP3 (CMIP5) las heladas tipo radiativas (advectivas) serían las favorecidas en la Pampa Húmeda debido a la posición del anticiclón.The purpose of this study is to investigate the change in the atmospheric circulation associated with frost events in the Wet Pampa (WP) in the future climate for the most critical scenarios projected by the GFDL ocean-atmosphere coupled model. Two versions of the GFDL model are used, the GFDL-CM2 for CMIP3 and GFDL-CM3 for CMIP5. We analyze the model capability to simulate the five most extreme cold events in the present climate (1961-1990), with respect to those obtained with the NCEP/NCAR Reanalysis. Then, we compare the future climate simulations (2081-2100) with the model simulation for the present climate. For the present climate the CMIP3 experiment presents more penetration of the 0°C isotherm in 850 hPa, intensifying the negative temperature anomalies in comparison to the reanalysis. The postfrontal anticyclone is more meridionally extended over the continent, with similar anomalies to those of the reanalysis, mainly over WP. The gradient between the high pressure and the low pressure downwind creates a more intense southerly cold airflow at 850 hPa than the reanalysis, giving place to advective frosts in the studied region. For the future climate, the model projects less penetration of the 0°C isotherm and less intense negative temperature anomalies. The anticyclone maximum is located further north than in the present climate, propitiating radiative frosts. In the upper levels, the subtropical jet shows a more zonally layout and slightly higher intensity than in the present climate simulations. For the present climate the CMIP5 experiment simulates well the incursion of the 0°C isotherm, although with a more intense temperature anomaly in comparison to the reanalysis. The pressure field presents similar characteristics to those shown in the CMIP3 experiment, but with larger anomalies in the southern part of the continent. For the future scenario, the model projects the 0°C isotherm incursion as well as the negative temperature anomalies similar to the present. The post frontal anticyclone is located further north, overestimating its value and the anomaly over WP. The wind field is similar to the present simulation. Summarizing the results of both experiments, the future projections with CMIP3 show significant changes with respect to the present, which is not the case with the CMIP5 experiment. These changes are mainly reflected in the pressure field, in which the position of the anticyclone in CMIP3 (CMIP5) would favor radiative (advective) frosts over WP.Asociación Argentina de Geofísicos y Geodesta

Variability in the annual cycle of the Río Atuel streamflows and its relationship with tropospheric circulation

Climate-induced changes in the annual regime of snow-fed rivers have serious implications for water resource management. In the Central Andes (CA, 28°–36°S) of Argentina–Chile, the snow accumulated in high-elevation mountains in winter is the dominant component of streamflows during the spring–summer melting season. Although topography introduces complexity in snowpack responses to the annual temperature cycle, streamflow series over a century in length make the CA particularly suitable for identification of long-term hydrological changes. Principal component (PC) analysis of Río Atuel annual hydrographs from 1906 to 2012 discriminates between precipitation- and temperature-related components associated with variations in snow accumulation (49% of variance) and advances/delays of the streamflow annual peak (21% of variance), respectively. The temporal evolution of PC1 loadings reveals a predominant negative period from 1917 to 1976 and from 1988 to present, suggesting the propensity to undergo long periods with reduced flows. In turn, the PC2 pattern is predominantly positive from 1948 to the present, revealing a tendency to more frequent peak flows in late spring since the mid-20th century. Above-average streamflows related to abundant snowfalls in the CA are associated with northward shifts in stormtracks that are remotely induced by above-average sea surface temperatures in the equatorial Pacific. On the other hand, earlier streamflow peaks in November-December are concurrent with above-average temperatures across the Atuel basin induced by enhanced meridional circulation from the Tropics due to the strengthening of the South Atlantic anticyclone. These circulation anomalies are linked to the persistent positive phase of the Southern Annular Mode during the last decades. Additionally, years with reduced streamflows in January, and proportionally larger flow contributions in November-December, are associated with anomalous air cooling at high levels induced by low pressure centres over the region as part of a quasi-zonal stationary Rossby wave train that extends from Australia to the South American–South Atlantic sector.Fil: Araneo, Diego Christian. 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; Argentina. Universidad Nacional de Cuyo; 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

Zonda wind classification using machine learning algorithms

Zonda wind is a typical downslope windstorm over the eastern slopes of Central Andes, in Argentina, which produces extremely warm and dry conditions creating substantial socioeconomic impacts. To achieve the Zonda wind classification, objective methods based on supervised machine learning (ML) algorithms are used. ML training and supervision is based on the subjective Zonda wind classification assessing the total hourly data that correspond to Zonda wind observations for three surface stations longtime series. ML algorithms includes; the linear discriminant analysis (LD), linear support vector machine (SVM), k nearest neighbours (k-NN), logistic regression (LR) and classification trees. Metrics obtained from the confusion matrix are used to compare the models' skills in class separation. Considering event-based statistics, the obtained probability of detection values locate all models above 85% with a probability of false detection lower than 0.523% and a missing ratio below 15%. From an alarm-based perspective, algorithms show values below 11.42% in false alarm rate, lower than 0.7% in missing alarm ratio and higher than 88.85% in correct alarm ratio. The false negative rate occurs mostly from August to December, where the onset time of the events presents greater difficulty in the classification than the offset, while the false alarm increases in June and October months. Models skills reveal that k-NN, SVM and LR are better discriminators than LD and classification tree. The high efficiency of these models indicates that ML classification models could be used for the phenomenon diagnosis.Fil: Otero, Federico. 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; ArgentinaFil: Araneo, Diego Christian. 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

Forecasting Zonda Wind Occurrence with Vertical Sounding Data

Zonda wind is a typical downslope windstorm over the eastern slopes of the Central Andes in Argentina, which produces extremely warm and dry conditions and creates substantial socioeconomic impacts. The aim of this work is to obtain an index for predicting the probability of Zonda wind occurrence. The Principal Component Analysis (PCA) is applied to the vertical sounding data on both sides of the Andes. Through the use of a binary logistic regression, the PCA is applied to discriminate those soundings associated with Zonda wind events from those that are not, and a probabilistic forecasting tool for Zonda occurrence is obtained. This index is able to discriminate between Zonda and non-Zonda events with an effectiveness close to 91%. The best model consists of four variables from each side of the Andes. From an event-based statistical perspective, the probability of detection of the mixed model is above 97% with a probability of false detection lower than 7% and a missing ratio below 1%. From an alarm-based perspective, models exhibit false alarm rate below 7%, a missing alarm ratio lower than 1.5% and higher than 93% for the correct alarm ratio. The zonal component of the wind on both sides of the Andes and the windward temperature are the key variables in class discrimination. The vertical structure of Zonda wind includes two wind maximums and an unstable lapse rate at midlevels on the lee side and a wind maximum at 700 hPa accompanied by a relatively stable layer near the mountain top.焚风是阿根廷中安第斯山脉东坡典型的下坡风暴, 可导致极其温暖干燥的气象条件, 并产生巨大的社会经济影响, 通过主成分分析法( análisis de componentes principales, PCA),析法辨识与焚风相关的探空数据, 得到焚风的概率预报模型。该指数能够区分焚风和非焚风事件, 有效率接近91%。最佳模型由安第斯山脉两侧的四个变量组成。从已发生的焚风事件的统计结果看, 混合模型的探测效率在97%以上, 空探测率低于7%, 漏探测率低于1%, 漏报率低于1,5%, 预报准确率高于93%时的垂直结构特征为背风坡中层的两个风速峰值区和不稳定温度递减率以及迎风坡700 hPa处的风速峰值和接近山顶处的相对稳定层。Fil: Otero, Federico. 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; ArgentinaFil: Araneo, Diego Christian. 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

Sea Surface Temperature and Atmospheric Circulation features associated to the Argentinean Andean rivers streamflow variability

Two zones are identified alongside the Argentinean Andes where river streamflows show similar time variability behavior. The zones are represented by the Chubut river (between the Neuquén and the Senguer) and the Atuel river (between the Jachal and the Colorado). It is noticeable the low correlation between the streamflows from one another, which means statistical independence between them. The different topography and climates give rise to differentiable hydric regimes as shown by the correlation between the streamflows with temperature and precipitation. The Atuel water-volume from November to March is a product of summer melting of high-Andean snows accumulated in the previous winter. In turn, the Chubut water-volume shows a maximum in winter due to winter precipitation, and a secondary peak in spring due to precipitation and snow-melting. The relationship between streamflows and sea surface temperature (SST) is significant in large areas of the Southern Hemisphere (SH) central Pacific. However, the Atuel variability seems to be highly linked to El niño / Southern Oscillation (ENSO) patterns with strong signal in the tropical-equatorial Pacific and the Indian Ocean, whereas the Chubut seems to be less associated with the ENSO, showing signal restricted to the SH central subtropical Pacific. High streamflows in the Atuel zone are associated with frequent passage of northwest-southeast oriented lows moving over the subtropical Pacific that induce moisture convergence from lower latitudes and its advection toward the Andean region. The lows reaching the central Chilean coast would produce upward air motion with intense snowstorms in the high mountains and downward air motion with relative high pressures leeward the Andes. Hence, over northeastern Argentina and southern Brazil, a later cyclogenesis would be produced and an increase in baroclinicity linked to a frontal zone with consequent moisture convergence from Brazil, upward air motion and high pre-frontal temperatures. In cases of high streamflows in the Chubut zone, the lows from the Pacific would reach the Chilean coast at higher latitudes, crossing over the natural further low Andes with no discontinuity and transporting moisture from subtropical latitudes. The subtropical low systems are linked to a remarkable reduction of the westerlies owing to higher frequency of highs from the southern Pacific. Some researchers associate these highs with equatorial SST anomalies and the decadal ENSO-like variability and they may take part of a wave-train from the Indian Ocean extended over the southern Pacific. The wave-train can be observed with the correlation between the Atuel streamflows and the geopotential height, but not for the Chubut streamflows. Inverse circulation and SST features would be associated to low streamflows in the studied regions.Pages: 693-70