Walter M. Vargas

Las sequías en la pampa húmeda: impacto en la productidad del maíz

This work seeks to identify droughts events in the space-time that occurred during the last century in Humid Pampas (Argentina). By means of the drought-index, statistical properties such as persistence, extremes and trends are analyzed. Since corn is drought sensitive, this study also attempts to show potential consequences of drought on the productivity of this important region crop. For that, an interaction model between droughts and productivity-impacts is elaborated and evaluated.

Joint Diagnostic of the Surface Air Temperature in Southern South America and the Madden–Julian Oscillation

Abstract The objective of this research is to explore the relationship between maximum and minimum temperatures, daily precipitation, and the Madden–Julian oscillation (MJO). It was found that the different phases of the MJO show a consistent signal on winter temperature variability and precipitation in southeastern South America. Additionally, this paper explores the spatial–temporal variations of mutual information and joint entropy between temperature and the MJO. A defined spatial pattern was observed with an increased signal in northeastern Argentina and southern Brazil. In the local mutual information analysis, periods in which the mutual information doubled the average values were observed over the entire region. These results indicate that these connections can be used to forecast winter temperatures with a better skill score in situations where both variables covary.

Climatic variability and Uruguay River flows.

Abstract The relationship between the climatic characteristics of a river basin and its hydrological response is very well understood. River flow is the synthesis of a broad range of phenomena such as rainfall, evapotranspiration, vegetation, soil, and geomorphological characteristics. This paper analyzes the Uruguay River in terms of its flow variability and the possible influences of the El Niño/Southern Oscillation (ENSO) phenomenon over a transition region between the subtropical and the mid-latitude regimes. A number of relationships were found between the warm, cold and neutral ENSO phases and the maximum floods of the Uruguay river. The conclusion of this work enhances knowledge of the climatic characteristics of the Uruguay river basin, and it may also be useful for flood forecasting.

Interaction Processes between the Annual Wave and the Disturbances in Series of Daily Temperature

Abstract Recently daily series of meteorological variables have been studied according to signal-noise patterns by different authors. Later on, the persistence phenomenon was modeled as an autoregressive structure of Markovian red noise. In series of daily anomalies obtained from filtered annual wave, a particular memory remains that is seasonally dependent. The method presented in this paper allows the modeling of (a) seasonal and intraseasonal variation of persistence, and (b) temporal distant action between perturbations. Data are showing that temporal distant action between perturbations would result from slow changes in border conditions, such as ENSO. Four examples of previous changes in the structure of daily extreme temperature series of San Miguel de Tucuman, Argentina, known as “season structure,” are shown. One of them corresponds to the El Nino/no El Nino dichotomic phenomenon.

Temporal analysis of precipitation and rain spells in Argentinian centenary reference stations

Different rainfall parameters are analysed in the present work in order to describe precipitation in three Argentine reference stations. These locations represent their precipitation climate region through a centenary data record. The selected parameters are annual accumulated precipitation, number of days with precipitation and precipitation intensity. All three stations indicate a positive trend in the first two variables over the studied period; moreover, because of a proportional increase, the precipitation intensity parameter has no significant variability. From the analysis of these variables and applying statistical methods, a climatic jump is found in each station, around the 1950s. A second focus of this work is the analysis of rain spells. To this end, a cutoff value for each station is found and used so as to establish the relationship between the accumulated precipitation and the frequency of rain spells per year. The total number of rain spells follows an exponential decay function for their relative frequency, considering the number of days that constitutes them. Rain spell characterisation allows for the understanding of their contribution to precipitation, according with its duration.

A Study of Intraseasonal Temperature Variability in Southeastern South America

AbstractThe main goal of this work was to conduct an intraseasonal climate variability analysis using wavelet and principal component analysis over a southeastern South American daily maximum and minimum temperature series from the end of the nineteenth until the beginning of the twenty-first century. The analysis showed that there is a definite and coherent signal in the intraseasonal maximum and minimum temperatures. The most noticeable signal was observed during the winter months. The frequency of the intraseasonal signal was more complex for the maximum temperature, and in some stations, it displayed a bimodal distribution. A defined pattern that described a coherent variability between 30 and 60 days throughout the entire region was observed. This pattern potentially allows classification of the regional variability and adjustments to the temperature forecasting models on a daily basis.

Latitudinal positioning of the subtropical anticyclone along the Chilean coast

In the past various authors have investigated climatic change (CC) by using the latitude of the subtropical ridge in the mean sea-level pressure (MSLP) for a range of geographic regions. In this paper the index L is defined as the latitudinal position of the subtropical anticyclone along the Chilean coast. This L index on the South American coast of the South Pacific is analysed using an instrumental record, covering the 1901-2004 period. An objective methodology is proposed for estimating L, and the physical consistency is assessed with the SOI and pressure at sea level in Valdivia, Chile. The analysis of a shorter period is compared with other authors’ results. The L variable can be useful in CC studies or in the analysis of low-frequency fluctuations in climate variability, and it is analysed as a dependent and independent time series. L was displaced towards the south over the last century but not to a statistically significant extent. Natural fluctuations of 50 years and another, shorter, of 16-22 years were also observed. In this paper, the greatest persistence and distant associations between anomalies of monthly L are shown; these associations can be useful for climate forecasting.

Mid‐troposphere variables and their association with daily local precipitation

This paper describes the meteorological variables directly affecting precipitation in the southern region of South America. Results show the relationships between daily precipitation at Ezeiza, Buenos Aires, and 500 mb dynamic variables (e. g. geopotential heights, relative geostrophic vorticity and its advection, vorticity tendency and zonal and meridional geostrophic wind components) using regional synoptic analyses from the Servicio Meteorologico Nacional of Argentina for 1986. The distribution of significant biserial correlation coefficients reveals the preferred positions for the anomalous wind components which favour the occurrence of rainfall at Ezeiza. In the same way, spatial distributions and temporal lag relations of 500 mb relative vorticity anomalies in relation to precipitation show the positions and relative movement of centres of anomalously cyclonic and anticyclonic vorticity which increase the probability of precipitation at Buenos Aires. Vorticity advection does not yield higher correlations, at least in a daily temporal scale. The geographical distribution of temporal means and standard deviations of geopotential heights and zonal and meridional wind components at the 500 mb level are also shown. Copyright

Study of homogeneity of precipitation in a region in the province of Buenos Aires, Argentina

SummaryMonthly and annual climatic variabilities of precipitation were analyzed from a 60 years record of rainfall data at 10 measuring stations in the humid region of Argentina.Different statistical techniques were used to analyze the regional homogeneity of precipitation fields. Special structures and monthly trends were studied. Simple correlations of yearly precipitation at different locations were computed. Exponential functions relating cross-correlations and distances were determined through regression analysis.Monthly and annual rainfall show no evident signs of trends; aleatory processes are predominant in the whole region; and, correlation functions are independent of the direction of the vector connecting the stations.

Variabilidad de Baja Frecuencia de la Persistencia de la Temperatura en el Sudeste de Sudamérica

Se analizan las estructuras de las autocovarianzas y autocorrelaciones de las temperaturas maximas y minimas en estaciones de referencia en el sudeste de Sudamerica. A traves de estas propiedades se observa que existen oscilaciones de periodos entre 18 y 25 anos en las series bajo estudio, aunque estas periodicidades presentan cambios con el tiempo, especialmente entre los anos 1950-1970. La excepcion es Rio Gallegos donde la periodicidad de 18 anos se observa durante todo el registro. La persistencia definida mediante el primer coeficiente de autocorrelacion es funcion de la cantidad de terminos de autocovarianza negativas. No obstante, durante algunos anos es dependiente de la magnitud de los terminos positivos dados por las irrupciones calidas o frias intensas. Entre los anos 1950 y 1970 se ha observado un aumento de la variabilidad con una alta alternancia entre periodos de mayor y menor persistencia. Estos cambios analizados en la persistencia sugieren una variacion en la frecuencia de distintos tipos de circulacion que tienen un impacto directo en la estructura termica regional. Asi mismo, variaciones de este tipo pueden tener serios impactos socio-economicos ya que estos afectarian directamente la frecuencia y duracion de los eventos extremos. Esto tiene importancia tambien en el diseno de metodos de control y consistencia ya que en ellos es posible considerar como outlier o informacion erronea los cambios producidos por las irrupciones de escala sinoptica mencionadas anteriormente.