Features of the Northwestern Argentinean low during the 1997-2003 period: selection criteria and statistical analysis

En este trabajo se proponen y analizan diversas metodologías para detectar eventos de Depresión del Noroeste Argentino (DNOA) con el objeto de poder documentar su posición, intensidad y duración media a lo largo del año, durante un período que va de marzo de 1997 a febrero de 2003. A través de una selección cuidadosa de eventos, se documentan diversos aspectos estadísticos de la DNOA, en base a un período sustantivamente mayor que cualquier otro antecedente al respecto, al tiempo que se comparan estos resultados con los obtenidos en trabajos pre-existentes. Los resultados muestran que durante el período de estudio se identifican similar cantidad de eventos de baja presión durante todas las estaciones del año, mostrando que la DNOA es un patrón dominante que caracteriza el clima de la región sur de Sudamérica. Asimismo, la cantidad de días bajo régimen DNOA es menor en invierno y en otoño, como así también la duración media de los eventos. Finalmente se encuentra que la posición media del mínimo de presión de la DNOA se ubica más al norte que la documentada por otros autores, y presenta una mayor variabilidad espacial en las estaciones cálidas que en las frías.In this paper we propose and analyze several methodologies to detect Northwestern Argentinean Low (NAL) events, in order to document its mean position, intensity, duration and their variability. The period of analysis encompasses from March 1997 to February 2003. Through a careful selection of events, various statistical aspects of the NAL are documented. This characterization is based on a period substantially longer than any other precedent in this regard, and results obtained are compared with previous ones. Our results show similar amount of low pressure events for all seasons, showing that the NAL events constitute a dominant pattern that characterizes the climate of southern South America. Also, the number of days under NAL regime is lower during winter and autumn, as well as the mean duration of the events. Finally, we found that the mean position of the NAL center turns out to be northward than documented by other authors, exhibiting larger spatial variability during the warm season than during cold one.Fil: Ferreira, Lorena Judith. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Saulo, Andrea Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; ArgentinaFil: Seluchi, Marcelo Enrique. Centro de Previsao de Tempo e Estudos Climaticos; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Relationship between ENSO cycles and frost events within the Pampa humeda region

The objective of the present paper is to analyse the possible impact of ENSO events on the spatial and the temporal distribution of frost occurrences, within the central region of Argentina. Therefore, the minimum temperature series have been studied for 41 meteorological stations within the Pampa Húmeda region and, for a period of 30 years from 1961 to 1990, exploring possible relationships with El Niño (EN)/La Niña (LN) events and the changes in the Southern Oscillation. It can be concluded that part of the frost frequency variability within this region is explained by the ENSO cycle. Results indicate that, for at least 1 of the 2 years in which the EN event takes place, the mean number of frost occurrences drops below the climatological value. The low phase of the Southern Oscillation Index (SOI) also coincides with those years for which the number of frost events remained below the total annual mean in all cases, with the year 1965 as an exception. Conversely, during the high phase of the SOI, this number was above the total annual mean for four of the six classified cases. In the particular case of seasonal frost occurrence, it is related to the warm event development state, exhibiting a greater impact during the autumn and winter months, for which the cold event also seems to have influence. Copyright © 2000 Royal Meteorological SocietyFil: Muller, Gabriela Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Nuñez, Mario Nestor. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Seluchi, Marcelo Enrique. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Vento tipo Foehn nas Serras do Sudeste do Brasil visto pela simulação do Modelo Eta

The present study gives evidence of the occurrence of foehn-like wind on the eastern slopes of the mountains at South-eastern Brazil. A particular case was detected based on observational evidence on 4 July 2015 near the city of Cruzeiro, state of Sao Paulo, on the Serra da Mantiqueira mountains. Results obtained from numerical simulations are consistent with the foehn wind occurrence deducted from the analysis of regional patterns and time series of selected meteorological parameters.O presente trabalho evidencia a ocorrência de vento tipo foehn nas encostas orientais das serras do Sudeste do Brasil. Um caso particular foi detectado a partir de evidências observacionais em 4 de Julho de 2015 perto da cidade de Cruzeiro, Estado de São Paulo, na Serra da Mantiqueira. Os resultados obtidos por simulações numéricas são consistentes com a ocorrência de vento foehn, como pode ser visto a partir da análise de padrões regionais e séries temporais de certos parâmetros meteorológicos.Fil: Antico, Pablo Luis. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - la Plata. Laboratorio Geo - Aggo.; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Chan Chou, Sin. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Seluchi, Marcelo Enrique. Centro Nacional de Monitoramento e Alertas de Desastres Naturais; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sueiro, Gustavo R.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; Brasi

A seca e a crise hídrica de 2014-2015 em São Paulo

During most of the rainy season in 2014, the Southeast of Brazil – including the Cantareira reservoir system – received below-normal rainfall. The main cause leading to that heavy lack of rain was an intense, persistent and anomalous highpressure system blocking moisture flow from the Amazon and the development and passage of cold front systems and the South Atlantic Convergence Zone, which are responsible for rainfall in this region during summer. This blocking system lasted for 45 days, which is extremely rare. Low rainfall amounts coupled with an increased demand for water and an inefficient water management system led to the so-called “water crisis” during 2014, which extended into 2015A maior parte da estação chuvosa de 2014 transcorreu com valores de chuva inferiores à média histórica sobre a porção sudeste do país, incluindo o Sistema Cantareira. A causa principal para a grande falta de chuva foi a atuação de um intenso, persistente e anômalo sistema de alta pressão atmosférica que prejudicou o transporte de umidade da Amazônia, assim como a passagem/ desenvolvimento dos principais sistemas causadores de chuva, como a Zona de Convergência do Atlântico Sul e as frentes frias. Esse sistema, denominado de bloqueio atmosférico, teve uma duração de 45 dias, fato que resulta extremamente raro. A combinação dos baixos índices pluviométricos, o grande crescimento da demanda de água e o ineficiente gerenciamento desse recurso têm gerado uma “crise hídrica” durante os anos 2014 e 201

A case study of a midtropospheric cold vortex in the subtropics of South America

Este trabalho descreve a estrutura sinótica-dinâmica de um vórtice de altos níveis sobre latitudes subtropi-cais da América do Sul. O centro ciclônico formou-se entre duas regioes baroclínicas associadas respectivamente a um sistema frontal e a uma perturbação proveniente do Oceano Pacifico. Com o objetivo de diagnosticar os processos físicos responsáveis pelo desenvolvimento do vórtice utilizou-se a equação da vorticidade, que foi avaliada com os diagnósticos gerados pelo modelo regional Eta/CPTEC. A advecção horizontal de vorticidade ciclônica e o termo da divergência foram os fatores que mais contribuíram na formação do sistema.Pages: 1674-168

Tropical-Mid latitude exchange of air masses in South America. Part II: Diagnostic of three cases study of extreme wather situations

Through of the three case studies, the effects and causes of the exchange of air masses between tropics and extratropics, were analyzed on some detail. The November 29, 1996 case showed that the Chaco Low favored the entrance of tropical air to higher latitudes, helping to increment the atmospheric instability which was later released by the passage of a frontal system. The June 30, 1996 event indicated that the freezing conditions in southern and southeastern Brazil were associated with the advance of a cold core anticyclone that moved rapidly to the north forced by a baroclinic wave of large amplitude and helped by the channeling effect of the Andes. Finally, incursions of frontal systems that reach subtropical latitudes in summer increment the convergence (divergence) in the lower (upper) levels on the region where SACZ is located. That was the case related to the storms and flooding in Ouro Preto, Brazil at the beginning of 1997.Pages:

Evaluación de una nueva versión operativa dei modelo regional Eta/CPTEC

En este trabajo se evalúa el desempeño de una nueva versión del modelo regional Eta/CPTEC (llamada Eta2d), que se diferencia de la actual (Eta1d) por un tratamiento más sofisticado de los procesos de superficie, un dominio de integración mayor y un tope atmosférico más elevado (50mb). Con este fin se analizaron los errores medios y cuadráticos medios de diversas variables, para un conjunto de 15 situaciones meteorológicas. Estos errores fueron obtenidos comparando los pronósticos con los análisis del NCEP y con sondeos aerológicos en varias estaciones. La precipitación fue evaluada a través del BIAS y el ETS. El análisis incluyó pronósticos a 24, 48 y 60 horas. Los resultados muestran que la versión Eta2d resulta mejor sobre todo el recinto de integración, y especiamente sobre la región amazónica. Dichas mejoras se hacen más evidentes luego de las primeras 24 horas de integración, fundamentalmente a través de la temperatura, la altura geopotencial y la humedad. En particular la inclusión de un nuevo modelo de suelo genera temperaturas de superficie notablemente más cercanas a las observadas. Otro cambio introducido fue el ajuste de los parámetros intervinientes en el esquema convectivo de Betts y Miller. El conjunto óptimo de coeficientes (logrados através de una extensa serie de experimentos de sensibilidad) permite mejorar la intensidad de la lluvia prevista y contribuye a disminuir los errores sistemáticos de otras variables

Diagnosing systematic errors in the eta model forecasts over South America

The Centro de previsão de tempo e Estudos Climáticos (CPTEC) has emplyed the Regional ETA Model to produce short-range forecasts on operacional basis since 1997. The model has become one of the most important tools for weather forecasts over South America. However, because of the short period of operation, it is necessary to identify the systematic biases and the various parameters suitable to the conditions of this continent to achieve improved forecasts.Pages: 422-42

Intercambios de masas de aire entre latitudes tropicales y estra tropicales de Sudamerica: validacion del modelo regional

The regional Eta/CPTEC model has been producing operationally forecasts over South America since 1996. The objective of this work is to evaluate the model predictions during strong meridional mass exchange over South America based on different model domain and grid-size configurations. Six cases of cold air intrusion and eight examples of warm air intrusion associated to convective activity over middle latitudes were chosen for the study. The model was evaluated against the NCEP global analyses, based on statistical verification parameters. Global analyses were interpolated bilinearly to the 40-km Eta model output grid. Larger forecasts errors were found close to the southern boundary of the domain in both cold and warm air cases. These errors suggest the presence of strong forcing near the southern boundary generating errors which propagate toward the interior of the domain. The substitution of the boundary conditions to analyses reduced substantially the errors in the interior. The unavailability of regional analyses limited the study. However the conclusion of large forecast errors being generated at the southern boundaries is apparent, and an increase in model domain is recommended for the 40-km version