Enhanced IR -cold ring analysis

18 September 2007, 06:00 UTC

The temperature scale is in °C, showing the coldest areas in red color.

18 September 2007, 06:15 UTC

At 6:15 UTC the formation of the "cold-ring" starts over the border of Slovenia and Italy.

 

18 September 2007, 06:30 UTC

At 6:30 UTC "cold-ring" was clearly visible on the Slovenian-Italian border and was identified until 7:30 UTC remaining almost stationary over NW Slovenia. The characteristics of the cold ring and the adjacent Central Warm Spot (CWS) were for this case the following:

• temperature difference between cold ring and CWS: 9 K
• CWS size: typically 3-4 SEVIRI pixels in diameter
• CWS duration: from 6:30 UTC to 7:30 UTC
  

This cold ring identification was clear indication about the penetration of the cloud tops into the tropopause.

18 September 2007, 06:45 UTC

Cold ring and the CWS are visible in NW Slovenia. Notice also the overshooting tops appearing at that point at the southern part of the cold ring , temperature -67°C. They are marked by the coldest cloud top temperature.

18 September 2007, 7:00 UTC

The storm crosses NW Slovenia.

18 September 2007, 7:15 UTC

The Central Warm Spot is getting colder.

18 September 2007, 7:30 UTC

Cold ring is still visible, but the CWS got very small.

18 September 2007, 7:45 UTC

At this point the first storm has moved to Austria, whereas a new one, again cold-ring shaped, is appearing over NW Slovenia.

18 September 2007, 8:00 UTC

The CWS in the new storm gets more pronounced, but the cold-ring is now hard to recognize because the two cells are merging.

18 September 2007, 8:15 UTC

From this point on cold ring could not be identified any longer.

18 September 2007, 8:30 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 8:30 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 8:45 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 9:00 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 9:15 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 9:30 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 9:45 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 10:00 UTC

New convective cells were developing in the NW and N Slovenia with different shapes, with the cloud top temperatures below -65°C.

18 September 2007, 10:15 UTC

A V-shaped cold area forms within the storm.

18 September 2007, 10:30 UTC

The shape of the cold area in the storm now resembles the V or U shaped storm. From the recent developments in that field it seems that the U or V shaped storms have the same origin as the cold-ring shaped storms. The only difference is that cold-ring shaped storms apparently develop in the environment with much less shear.

18 September 2007, 10:45 UTC

The shape of the cold area in the storm now resembles the V or U shaped storm. From the recent developments in that field it seems that the U or V shaped storms have the same origin as the cold-ring shaped storms. The only difference is that cold-ring shaped storms apparently develop in the environment with much less shear.

18 September 2007, 11:00 UTC

Small cells with very cold tops appear again over NW Slovenia.

18 September 2007, 11:15 UTC

Small cells with very cold tops appear again over NW Slovenia.

18 September 2007, 11:30 UTC

Small cells with very cold tops appear again over NW Slovenia.