Juan L. Minetti

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.

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.

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.

Trends of the Drought Indices in Southern Hemisphere Subtropical Regions

With the use of droughts indexes on Subtropical South Hemisphere, we have detected: a) statistically stationary conditions on average during the period 1880-1980 and b) an important positive tendency to droughts between 1980-2013. This recent tendency to regional droughts is coincident with the actual processes of Global Warming. The hypothesis of an acceleration of the Hadley Circulation (HC) is present with global warming, which would reduce precipitation in subtropical aridsemi arid zone and increase rainfall in the Intertropical Convergence. This process was confirmed by the precipitation data of Reanalysis I, with an inverse correlation between the two regions. These droughts indexes also show the more presence of an interdecadal variability signal (PDO) and El Niño/South Oscillation (ENSO) at low and high frequencies. Most of the variances in these regions have been explained by long climate changes. ENSO high frequency changes are present and they behaved in an inverse way as expected between both South Pacific Ocean coasts. When the group was analyzed as a subtropical anticyclone band or regional in Chile, Australia and South of Africa, it did not disturb the large-scale signs that are highlighted in this study. KeywordsTrends; Droughts Index; Subtropical South Hemisphere