Activité cyclonique et rythmes climatiques aux latitudes moyennes (lre partie)

The distribution of extratropical cyclones is characterized by a zonal organisation and an oceanic dominance. Most of the disturbances travel between the 40 th and 65 th parallels. These heat engines transform a part of the potential energy into kinetic energy. That potential energy derives from the strong thermal gradient which is connected with the convergence of polar and tropical influences. The Ocean, which forms a latent heat source, stirs up the cyclonic processes, too. The cyclones make up the features of seasons. A low (12.3 % of the annual total) and more uniformely spread cyclonic activity is typical of the summer months ; winter is marked by an exacerbation of disturbances (37.1 %) Intermediate seasons do not show such contrasting features. Spring which intensifies the action of the cold arctic and continental sources, totalizes 23.2 % of the whole cyclonic activity. On the other hand, autumn (27.4 %) stirs up the warm tropical maritime source. The cyclones represent a main factor by differentiating regional climates of Western Europe ; they also explain the seasonal distribution of precipitations along the Atlantic neighbouring lands.Trzpit Jean-Paul. Activité cyclonique et rythmes climatiques aux latitudes moyennes (lre partie). In: Norois, n°97-98, Avril-Juin 1978. pp. 69-85