EUMeTrain: Cyclogenesis in the Mediterranean 27-29 February 2004

27 February 2004, 00UTC

General information:

The image shows two prominent features:

1. - a dissipating cyclone over Central Europe and
2. - a new development in the Bay of Biscay, where the cloud band is already forming a spiral.

The latter is the development that will be followed in the next time-steps.

27 February 2004, 00UTC

Geopotential Height 1000 hPa.

A low over Italy is connected to a dissipating system. A small low is seen over the Bay of Biscay indicating a new cyclone developing there. The cloud band connected to that low already has a spiral shape.

27 February 2004, 00UTC

Height of PV=1.

The development has started between Ireland and France, moving southeast. The PV anomaly is already well defined. The height of PV=1 unit is found at 550 hPa meaning that stratospheric air has protruded to mid troposphere. Just for comparison: the old dissipating cyclone over Mid-Mediterranean and Central Europe has PV=1 unit at 350 hPa.

27 February 2004, 00UTC

Isotachs at 300 hPa

Northerly jet stream turns to north-westerly over Spain. The new developing cyclone is located in the left exit region of the jet streak. The other jet over the Mediterranean is connected to the old dissipating cyclone.

27 February 2004, 00UTC

Positive Vorticity Advection 300 hPa

In the region where the cyclogenesis starts, near the Bay of Biscay, there is a maximum of positive vorticity advection in the left exit region of a jet streak coming from the north. The advection of positive vorticity obviously favoured cyclogenesis in that region. The other maximum of positive vorticity advection, above Adriatic and Central Europe is connected to the dissipating cyclone.

27 February 2004, 00UTC

Temperature Advection at 700 hPa

At this stage the distribution of the temperature advection is still governed by the dissipating cyclone over the Adriatic, with warm advection in the cloud head over Central Europe. Cold advection over the Atlantic is getting stronger in the region behind a developing cloud band.

27 February 2004, 00UTC

Temperature Advection at 300 hPa

The distribution of the temperature advection in upper troposphere is guided here by the cyclone dissipating over Italy and Adriatic. In the region of new development, in the Bay of Biscay, there is warm advection maximum within the cloud band and cold coming from the north behind it.

27 February 2004, 00UTC

Shear Vorticity at 300 hPa

The distribution of the shear vorticity is governed by the jet stream. The zero-line of shear vorticity shows the location of the jet axis. On the left-hand side of the axis (looking windward) there is a maximum of positive (cyclonic) vorticity, whereas on the right-hand side there is a maximum of negative (anticyclonic) vorticity. In the region where the development takes place, there is positive (cyclonic) shear vorticity.

27 February 2004, 00UTC

Curvature Vorticity at 300 hPa

Curvature vorticity is at this stage strongest in the Bay of Biscay. This maximum of cyclonic vorticity is connected to the developing cyclone.