Teleconnections Between Tropical-Extratropical Oceans And The Daily Intensity Of Extreme Rainfall Over Argentina

ROBLEDO, FEDERICO ARIEL; PENALBA, OLGA; MARIA LAURA BETTOLLI

Foz do Iguazu

Conferencia; The Meeting of the Americas; 2010

American Geophysical Union

The main goal of this work is to identify the different ENSO regions of the oceans related with the extreme rainfall in Argentina, the tropical and subtropical Atlantic Ocean and the Indonesian Sea, in addition to areas of the Indian Ocean that influence Argentina?s extreme rainfall. We have explored the covariability between sea surface temperature (SST) for all the oceans from 17.5º N to 90º S and the daily intensity of extreme rainfall in Argentina. This analysis was performed using a Singular Values Decomposition for three austral seasons (spring, summer and autumn). The analysis was performed in the period 1962 to 2005 using two data sets: monthly SST from the Kaplan SST V2 from the NCEP/NCAR and high quality daily rainfall for 35 surface stations from the National Weather Service of Argentina distributed throughout the country.The monthly mean of daily intensity of extreme rainfall index (DIER) is the quotient between the monthly accumulated extreme rainfall (AE) and the number of days with extreme precipitation events per month (PE). We consider extreme daily precipitation when rainfall is greater than the mean 75th daily percentile for the period 1961 to 2000. Equation 1 represents the DIER index and was performed for each of the 35 meteorological stations. The wavelet transform was applied to the SVD time series of the SST to analyze the dominant cycles and their period of occurrence. The five leading SVD modes of the coupled SST and DIER variations account for around 70 percent for summer and autumn and 80 percent for spring of the total square covariance (TSC). The large percentage of the covariance explained by the first SVD mode, for all seasons, suggests a fair degree of predictability between the DIER and SST. Spring registers the highest SCF ?45 percent, whereas summer and autumn register 34 percent. These SST patterns have 4-year temporal cycles like the ENSO phenomena with an enhanced DIER in central and eastern Argentina. In the second SVD mode, spring has the highest SCF, 17 percent, whereas summer and autumn register 11 percent. For autumn and summer the tropical and subtropical Atlantic presents covariability with the DIER in central Argentina. Spring presents covariability in the Atlantic Ocean as well as in the Indonesian Sea. This mode shows a significant decadal variability with two sub-periods: 8 years and 12 years. In the third SVD mode of spring and summer the SCF are 10 percent and 6 percent, respectively; the Indian Ocean presents covariability with the DIER in the north and the eastern portion of Argentina, respectively. This mode shows a significant period of variability, around 14 years. In autumn the third mode presents a significant correlation of the tropical Atlantic Ocean and extreme rainfall in the center and eastern Argentina, with significant period of 14years. The SST regions identified in this study are another step in the continuing process of establishing the causes of low-frequency variability in the southern hemisphere.