A statistical measure of severity of Ei Nino events

El Nino exerts a significant influence on climate, and hence tremendously affects human activities. The monthly Southern Oscillation Index (SOI) is used to quantify El Nino events. The severity of El Nino is determined by a combination of its maximum intensity, magnitude, and duration that may be mutually correlated. However, the past analyses on the statistical properties of Ei Nino events either only take into account their occurrences or nonoccurrences, or simply rank El Nino events by a few categories such as most severe, severe, and less severe. Apparently, these analyses can not give a complete description of El Nino events. This article sheds new light on the statistical properties of El Nino events. The Gumbel logistic model, a bivariate extreme value distribution with Gumbel marginals is employed to analyze joint probability distributions of El Nino maximum intensity and magnitude, El Nino magnitude and duration, as well as El Nino maximum intensity and duration. Based on the marginal distributions of El Nino maximum intensity, magnitude, and duration, the joint distributions, conditional distributions, and associated return periods of two Of these El Nino characteristics can be readily obtained. Results indicate that statistics of El Nino events can be represented by the proposed method. The proposed method provides a much more detailed description of the properties of El Nino events than do the past approaches. It is also prior to single-variable frequency analysis.