Rapid Cyclogenesis over Ionian Sea

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Rapid Cyclogenesis over Ionian Sea cancelled all marine activities and caused flooding and structural damage in early February 2012.

Date & Time
06 February 2012 03:00 UTC
Satellites
Meteosat-9, Oceansat-2, WINDSAT
Instruments
SEVIRI, ASCAT
Channels/Products
Water Vapour, Airmass RGB, ASCAT winds

A surface depression originated at the Gulf of Sidra across the Libyan coast of northern Africa on 6 February 2012, and deepened rapidly as it moved northwards to the Ionian Sea.

The cyclone produced deep convection with excessive rainfall amounts over Greece and a very strong surface pressure gradient, with surface wind speeds exceeding 41 kts/76 km/h (9 on the Beaufort Scale) for many ground-based stations.

The storm caused two casualties, which resulted from drowning, significant damage and destruction, with trees being uprooted; extensive flooding; electrical grids being affected, cutting off power to some islands, and serious trouble in marine communications and transportation in general.

The intensity of both the wind field and the convective precipitation for this event is quite well forecast; on-time warnings for Port Authorities and the public were issued and broadcast.

More information and detailed analysis of the feature can be found in the In Depth section.

 

In Depth

By Kyriaki Metheniti (Hellenic National Meteorological Service)

In the satellite imagery below we can see that the position of the jet streams, a deformation area at the early stages of the developing cyclone, and a baroclinic leaf on the cold side of the southern subtropical jet, all indicate indicate rapid cyclogenesis (Figure 1). A scalloped pattern can be seen at the northern side of the baroclinic leaf.

Consecutively, the system evolved into a comma cloud and finally into a vortex with a bent back structure of the occlusion (Fig. 2-4). These are typical features of a rapid cyclogenesis development.

Figure 1: Met-9, 06 Feb 2012, 00:00 UTC
Water Vapour
Figure 2: Met-9, 06 Feb 2012, 06:00 UTC
Water Vapour
 

Figure 3: Met-9, 06 Feb 2012, 12:00 UTC
Water Vapour
Figure 4: Met-9, 06 Feb 2012, 18:00 UTC
Water Vapour

The rigorous circulation of the surface depression helped maintain strong winds over Greece on the following day (7 February). At the same time a prominent vortex with an occlusion form was retained, as seen in the water vapour imagery (Figures 5 & 6).

Figure 5: Met-9, 07 Feb 2012, 06:00 UTC
Water Vapour with MSLP overlaid
Figure 6: Met-9, 07 Feb 2012, 12:00 UTC
Water Vapour with MSLP overlaid

By 7 February at 12:00 UTC the rapid cyclogenesis was over. The surface low pressure system over the south eastern Ionian Sea started to fill up with gradually relaxing winds and eventually split up into smaller-scale vortices while making landfall.

All the above are summarised in the Airmass RGB images from the archive of EUMeTrain.

On Figure 7 a mature cyclone with an occlusion can be identified. There is also a red coloured stripe that surrounds almost entire vortex — an indication of stratospheric air protruding downward into the troposphere.

The warm front band shown by the high clouds in white on the right side marks the boundary of air masses of different temperatures.

Eighteen hours later, as shown on Figure 8, the warm front band displaced further to the east and a deep cyclonic vortex was situated over the eastern Mediterranean.

Within the occlusion a comma cloud and an enhanced cumulus area behind the frontal cloud band can be identified.

Figure 7: Met-9, 06 Feb 2012, 18:00 UTC
Airmass RGB (Source: EUMeTrain)
Figure 8: Met-9, 07 Feb 2012, 06:00 UTC
Airmass RGB (Source: EUMeTrain)

Assessment of the marine environment using scatterometry

Figure 9: ASCAT 25 km NOAA winds, 6 Feb, morning
Figure 10: ASCAT 25 km NOAA winds, 6 Feb, evening

An overall insight into the wind circulation close to the sea surface, in the case of the rapid cyclogenesis described above, is given through satellite-retrieved scatterometry data from ASCAT. The ASCAT ocean surface winds are 10 m neutral stability winds.

ASCAT did not always provide a full view of the depression's wind patterns due to its coverage limitations, but the depiction of the wind fields on the available images show additional information on the position of the surface fronts and the location of pressure minima.

Figure 11
 
Figure 11: ASCAT 25 km NOAA winds, 7 Feb, morning

The three ASCAT plots, during the different phases of the development, show how the regime with intense winds moved between 6 and 7 February.

During the morning of 6 February the 10 m wind field (Figure 9), as measured by ASCAT with a 25 km resolution, shows a wide area of wind speeds exceeding 30 kts/56 km/h.

The position of the low pressure system along with the frontal/convergence wind patterns is quite prominent.

Figure 10 shows the last available satellite passage from that day, again from ASCAT, corresponding to time measurements between 18:00 and 20:00 UTC at 35N.

Although a large portion of the maritime area of interest lays just below the satellite's swath gap, 45 kts/83 km/h wind speeds expanding from 15E to 27E were retrieved. The time coincides with the observed minimum pressure of 982 hPa at 18:00 UTC.

The final ASCAT image (Figure 11) shows the wind field during the landfall of the system on the morning of 7 February.

Read Kyriaki's full report Rapid Cyclogenesis over Ionian Sea (PDF, 3 MB)

 
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