Generalized extreme wind speed distributions in South America over the Atlantic Ocean region

Abstract

Statistical analysis of extreme values is applied to wind data from National Centers for Environmental Prediction and National Center for Atmospheric Research reanalysis grid points over the ocean region bounded at 23°S and 40°W and 42°W towards the south and southeastern Brazilian coast. The period of analysis goes from 1975 to 2006. The generalized extreme value and generalized Pareto distributions are employed for annual and daily maxima, respectively. The Pareto–Poisson point process characterization is also used to analyze peaks over threshold. Return levels for 10, 25, 50, and 100 years are calculated at each grid point. However, most of the reanalysis data fall within 1–10-year return periods, suggesting that hazardous wind speed with low probability (return periods of 50–100) have rarely measured in this period. Wide confidence intervals on these levels show that there is not enough information to make predictions with any degree of certainty to return periods over 100 years. Low extremal index (θ) values are found for excess wind speeds over a high threshold, indicating the occurrence of consecutively high peaks. In order to obtain realistic uncertainty information concerning inferences associated with threshold excesses, a declustering method is performed, which separates the excesses into clusters, thereby rendering the extreme values more independent.