Investiga？？o do Modo Sul em dados de precipita？？o no período de 1982 a 2006 no estado do Rio Grande do Sul

this work presents a study of a rainfall variability mode that acts in southern brazil and is called "modo sul" of precipitation. it was tried to show that the occurrences of maximum (and minimum) of the "modo sul" of precipitation are related to the occurrence of extreme events in rio grande do sul, as windstorm, flood, hail and drought. using principal component analysis of daily filtered precipitation data for the 10-50 day band we found spatial pattern and temporal series that represent the maximum variance of certain variabilities, which are the modes of precipitation variability. thus, it was possible to determine the mode of variability that appears well established in rio grande do sul. the principal component series was used to select the extreme events. the "modo sul" was calculated for the period from 01/03/1982 to 31/05/2006. it was possible to realize that the extreme rainy events were more frequent than extreme dry events. in a decadal analysis an increase in the number of events was found when comparing the 80s, 90s and 2000. it is noteworthy that the number of events of 2000s compared with the 80s was proportionally the most expressive.