New paradigms of mid-latitude cyclones: classification of development phases.

The homogeneous reanalysis by the European Centre for Medium-Range forecast of all the weather data collected between 1979 and 1993 is used to build c omposites of North Atlantic mid-latitude cyclones. In a limited area, betwe en 15 October and 15 April of the 14 winter seasons, vorticity maxima are a utomatically tracked. This yields more than 17 600 life-cycles. A property of this set is the very large diversity of life-cycles that leads to compos ite particular phases of the life-cycles, not the full cycles. Here, the 24 h of the largest development, ending with the maximum amplitude, is taken. Seven classes are obtained, showing that the only mechanism for deepenings larger than 10 mbar is baroclinic interaction, not to be confused, however , with baroclinic instability. (C) 2000 Academie des sciences / Editions sc ientifiques et medicales Elsevier SAS.