Cyclone monitoring using the Airmass RGB product.
21 October 2020
31 May 2006
by Jochen Kerkmann (EUMETSAT)
On 31 May 2006 Meteosat-8 captured an interesting case of double lee cyclogenesis: one to the lee of the Norwegian mountains and one to the lee of the Alps (Genoa cyclone). With the help of the so-called Airmass RGB product the PV (Potential Vorticity) maxima that caused the cyclogenesis could be monitored many hours before the cyclones formed.
The upper image shows the situation at 00:00 UTC on 31 May. A PV maximum at high levels can be seen to the north of the North Sea (marked by reddish colour (see Interpretation ). At this stage of the development there is no indication of a cyclonic circulation at lower levels (looking at the cloud structure). As the PV maximum moves over the Norwegian mountains, a cyclone starts to form over Denmark. The second image shows the situation at 06:00 UTC on 1 June when the spiral structure of the young lee cyclone is already clearly visible.
Similarly, the reddish colour over France in the upper image indicates the upper-level PV anomaly that caused the cyclogenesis over the Gulf of Genoa. In this case there is already some (weak) indication of cyclonic circulation given by the structure of the mid-level clouds.
The cyclogenesis to the lee of the Alps can be nicely followed by looking at the animation (see link below the upper image). Typical for this type of Genoa cyclogenesis (North-westerly 'Ligurian' type), the young cyclone moves quickly towards the south-east bringing little or no precipitation to North-eastern Italy (Veneto, Friuli). The more dangerous Genoa cyclones for the Alpine region are indeed the ones that form in a south-westerly flow (south-westerly type) when moist Mediterranean air gets lifted up the southern slopes of the Alps.
Meteosat-8 Airmass RGB Product
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