07-174 A. dell'Aquila, M. Felici, V. Lucarini, P.M. Ruti, A. Speranza, R. Vitolo
Extreme value statistics of mid-latitude atmospheric variability with present-day and increased CO2 concentration (1354K, PDF) Jul 6, 07
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Abstract. The General Circulation Model ECHAM4.6 is run under perpetual January conditions with two different values of CO2: the present concentration and five times as much. For each case, time series of two indexes of mid-latitude wave activity are computed. The mean activity of baroclinic waves and of planetary waves decreases slightly, following the decrease of the mean baroclinicity of the system. Inference of extreme values is performed by estimating the parameters of the Generalised Extreme Value (GEV) distribution from sequences of maxima over data blocks of fixed length extracted from the time series. The sensitivity and goodness-of-fit of the inferences are assessed by various graphical and numerical tools. The results reveal no marked differences in the statistics of extreme values between the cases with 1 and 5 CO2 and also suggest that the often invoked approach of relating changes of the extremes to changes in the mean and standard deviation of the bulk statistics is not reliable. Maps corresponding to the dates of the extremes (block maxima) of the indexes show that the relative weight of the wave activity of the Atlantic sector increases with CO2 concentration.

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