EUMeTrain: Case Study on an unusual rapid cyclogenesis

Summary

This case shows a very intensive development from a small scale comma to a synoptic scale cloud spiral. What makes this case so special lies in the fact that the cloud configurations on the one hand are deviating from the usual development process of an occlusion spiral and the configurations of relevant parameters demonstrate a situation with a high potential of development from the very beginning on and during the whole process.

Looking at the parameters relevant for cyclogenesis on isobaric as well as on isentropic surfaces (Vertical Cross Sections) there are many indications for a rapid cyclogenesis going on. But from the optical impression this case starting in polar latitudes develops differently compared to the well-known rapid cyclogenesis developments starting in the mid-latitudes over the Atlantic.

From the optical impression one would say that a Cold Air Development takes place. And some of the parameters do indeed support this, but the comma spiral from which the synoptic-scale spiral develops is not in the cold air but (probably) at a baroclinic boundary in the cold air.

Another very interesting feature of this case is the period of several hours during which very small scale curls develop at this boundary under the influence of dry air in upper levels which represents a PV anomaly.