It is a pleasure to thank D. Kondrashov for providing the code to preprocess the data used in this article and for his advice in using it. This work grew up out of a DEA diploma project carried out by AD under the guidance of MG and O. Talagrand; both AD and MG appreciate O. Talagrand’s input. RB would like to thank the Ecole Normale Supérieure and the Ecole Polytechnique for their hospitality and support during a sabbatical term in Paris. Support for this work was provided by NSF Grants SES04-37169 (RB) and ATM00-82131 (MG), as well as by the European Commission’s Project 12975 (NEST) “Extreme events: Causes and consequences (E2-C2)” (FD and MG).
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