Accessing extremes of mid-latitudinal wave activity: methodology and application |
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| Authors: | R VITOLO P M RUTI A DELL'AQUILA M FELICI V LUCARINI A SPERANZA |
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| Institution: | PASEF –Physics and Applied Statistics of Earth Fluids, Dipartimento di Matematica ed Informatica, Universitàdi Camerino, Via Madonna delle Carceri –62032 Camerino (MC), Italy;;ENEA, via Anguillarese 301 –00060 S. Maria di Galeria, Roma, SP 091 Italy;;Dipartimento di Matematica U. Dini, Universitàdi Firenze, viale Morgagni 67/A –50134 Firenze, Italy;;Dipartimento di Fisica, Universitàdi Bologna, viale Berti Pichat 6/2 –40126 Bologna, Italy |
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| Abstract: | A statistical methodology is proposed and tested for the analysis of extreme values of atmospheric wave activity at mid-latitudes. The adopted methods are the classical block-maximum and peak over threshold, respectively based on the generalized extreme value (GEV) distribution and the generalized Pareto distribution (GPD). Time-series of the 'Wave Activity Index' (WAI) and the 'Baroclinic Activity Index' (BAI) are computed from simulations of the General Circulation Model ECHAM4.6, which is run under perpetual January conditions. Both the GEV and the GPD analyses indicate that the extremes of WAI and BAI are Weibull distributed, this corresponds to distributions with an upper bound. However, a remarkably large variability is found in the tails of such distributions; distinct simulations carried out under the same experimental setup provide sensibly different estimates of the 200-yr WAI return level. The consequences of this phenomenon in applications of the methodology to climate change studies are discussed. The atmospheric configurations characteristic of the maxima and minima of WAI and BAI are also examined. |
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