EUMeTrain: Cyclogenesis in the Mediterranean

Meteorological Physical Background

Cyclogenesis is a complex process that can be dependant on the region where it happens and the processes in the background of it. Therefore it can be looked upon from different perspectives. In general the explanation of the process of cyclogenesis is contained in the following theories:
  1. Cyclogenesis according to the classical polar front theory
  2. Orographic lee cyclogenesis
  3. Cyclogenesis in connection with the left exit and the right entrance region of a jet streak
  4. The Hoskins theory based on PV and PV anomalies
In this case study there were actually two cyclones analyzed, but most attention was paid to the cyclone developing in the Mediterranean. For that development some of the mentioned theories can be applied better then the others:
Ad1. Cyclogenesis according to the classical polar front theory

This theory can most certainly be applied to the first cyclone, developing in the Bay of Biscay, since that cyclone had a course of development from a cold front cloud band to the occlusion in a classical way. However, the development in the Mediterranean was different in the beginning. When it already started, triggered on one hand by the existing cyclone and on the other hand by jet, it then followed more or less the classical theory in the part of developing an occlusion.

Ad2. Orographic lee cyclogenesis

Orographic influence could also be a part of the process, since the cyclone in the Mediterranean developed while the original cyclone from the Bay of Biscay was crossing the Pyrinees. However, it seems that Jet streak and the influence of vorticity distribution because of the Jet, played more important role.

Ad3. Cyclogenesis in connection with the left exit and the right entrance region of a jet streak

In this case the development of a cyclone was closely related to the vorticity advection maxima, connected to the left exit region of a jet streak.

Ad4. The Hoskins theory based on PV and PV anomalies

The ifluence of the protruding dry air is most easily detectable in the beginning of the process in the Bay of Biscay. There not only PV field, but also dry areas in the WV images show that the process of cyclogenesis was clearly triggered from above. Further on, when the development of the cyclone in the Mediterranean started it was clear that PV anomaly moved towards that region, whereas it got weaker in the region of the original development.