ÍNDICE DE NEBULOSIDADE DO ESTADO DO RIO GRANDE DO SUL: CLIMATOLOGIA E IMPACTOS DO EL NIÑO OSCILAÇÃO SUL

Abstract

The purpose of this study was to study the climatology of impacts from El Nino South Oscillation (ENSO) phenomena over the diurnal cloudiness of Rio Grande do Sul state. Moreover, we determine the predominant kinds of clouds in both phase of ENSO through a case study. Therefore, we used decendial and monthly sunshine duration data from 17 weather stations widely distributed in the Rio Grande do Sul state, for 1960 to 2005 period. For cloudiness classification we used a cloud-classification algorithm developed by CPTEC. The results showed that from October to December the biggest differences were observed between diurnal cloudiness index (DCI) in two ENSO phases in both monthly and decendial analyses. The behavior of the El Nino events compared to the neutral years was well defined, with the indexes remaining higher throughout the year in the former case. In the La Nina events the probability of smaller DCI was higher than for neutral years in southern half of the state. The greatest ENSO impact period on DCI, for both El Nino and La Nina, was from the end of spring to the end of summer.