EUMeTrain: Cyclogenesis in the Mediterranean

Satellite Images and Derived Meteorological Parameters

Basic parameters like surface pressure (height of 1000 hPa) or 500 hPa height do not reveal the whole physical background of a situation and can therefore neither explain details seen in the cloud features of satellite images nor the different conceptual models. Therefore, in order to understand the processes that lead to certain cloud configurations, it is usually necessary to consult different derived physical parameters.

Parameters and parameter combinations which can be helpful in the diagnosis of cyclogenesis are:

The basic theoretical background to the above mentioned parameters can be found in Manual of Synoptic Satellite Meteorology in the chapter BASICS.

In the following chapters you can see the development of a cyclone by looking at the satellite images overlayed by the mentioned meteorological parameter fields:
Height of PV = 1 unit (stratospheric air)
Parameter which greatly contributes to diagnosis of cyclogenesis is Potential Vorticity (PV). Maxima of PV (positive anomalies) indicate stratospheric air protruding downward. This is a process which triggers or enhances cyclogenesis. (See Physical Background - Hoskins theory).

The field of height of PV=1 unit is displayed and described here in a 6-hourly sequence.

Isotachs + PVA at 300 hPa
Isotachs at 300 hPa show the location of the jet stream while PVA in the same level is an indication for areas where it becomes more cyclonic and where there is additional upward motion. The typical configuration is a maximum of PVA at the left exit region of the jet streak. (See Physical Background - Jet streak ).

Isotachs and vorticity advection at 300 hPa are displayed and described in a 6-hourly sequence.

Temperature Advection at 700 hPa

Temperature Advection at 300 hPa

Temperature advection reflects cyclonic rotation which leads to a pattern of a Warm Advection maximum within the cloud bulge and a Cold Advection maximum in the cold air behind it.

Fields of temperature advection at 700 hPa and 300 hPa are displayed and described here in a 6-hourly sequences.

Vorticity components at 300 hPa

Shear vorticity and curvature vorticity at 300 hPa are displayed and described here in a 6-hourly sequence.

To get closer and more complex look into the situation, you can play with various combinations of meteorological fields by using Interactive Overlays.

Summary of the investigations in this chapter

The derived meteorological parameters reveal many details of the transition phase between an already existing cyclone coming from the Bay of Biscay and the new one developing in the Mediterranean.

Potential vorticity field actually looks like a field connected to one cyclone. The highest positive anomaly can be found north of Ireland, and can be further followed across southern France and northern Spain into the Mediterranean and further into Adriatic. In other words, looking at the PV field only, the conclusion could be that there was one cyclone triggered north of Ireland and moving towards the Adriatic. However, combination with relevant satellite images reveals that the original cyclone died of over France, whereas a new one developed in the Mediterranean.

Besides the already existing cyclone, the additional triggering mechanism for the development in the Mediterranean was the Positive vorticity advection (PVA), connected to the jet stream. The PVA maxima follow exactly the course of the development and the path of the cyclone.

Temperature advection shows the distribution typical for both cyclones and a very interesting transition phase between.