Extratropical Secondary Cyclones: Simulations and Observations,

Extratropical cyclones are observed over a broad spectrum of spatial scales synoptic-scale primary cyclones 1,OOO km, intermediate-scale secondary frontal-wave cyclones 1OOO km, and the lesser mesoscale cyclones 5OO-lOO km. The fundamental difference between primary and secondary cyclones was described by Eliassen 1966 A natural conclusion from the various theories is that the large-scale cyclonic systems associated with the transient waves in the upper-westerlies are the primary perturbation systems, since their existence can be accounted for by baroclinic instability, even in the absence of fronts. These large cyclonic systems, in turn, produce the fronts, partly by setting up the deformation fields required in Bergerons theory and partly by the non-linear process demonstrated by Edelmann. Finally, the fronts will give birth to the smaller frontal wave SECONDARY cyclones.