NWCSAF: Meteosat IR10.8 with ASII NWP overlay

Up till this point the products of the NWC SAF thus seen only identified and characterised the areas in the cloudfree regions. Two products that identify and characterise clouds are ASII and ASII-NWP. Where ASII stands for Automatic Satellite Image Interpretation.

The basic concept of ASII is the identification of:

• Detection of frontal areas
• Detection of S-shaped lines
• Detection of circular-shaped cells
• Detection of narrow cloud fibres
• Detection of black stripes in WV images
• Detection of spiral cloud structures

A segmentation divides the IR and WV satellite images into sub-regions being coherent in terms of brightness and texture. The classification process assignes qualities of different conceptual models to these coherent areas. At 06UTC the convection over Austria, Czech Republic and Poland has not started but concentrating on the frontal system on which the convection starts some interesting thing can be identified. The front is marked by c, • , w, m and ~ . Where

• c stands for Cold Front
• di the dry intrusion of stratospheric air into the area of cyclogenesis
• w denotes the Warm Front cloudiness
• z are the open and closed cell convection found in the CA behind the fornts.
• co comma clouds

In the first image we see the frontal depression still over Western Europe. From the occlusion spiral some open and closed cell convection has detached. A Comma cloud is situated over Southern Sweden, most likely bringing some snow.

As the time evolves slowly to the 18th November, the big depression (a.k.a. Quimburga) moves in over the North Sea. The dry intrusion gives some sign of the still ongoind cyclogenesis and the deepening of the surface low.

On the 17th November at 21UTC the first signs of the RaCy are observed. The baraoclinic leaf is recognised and is analysed as a wave. The F represent the cloud fibres as a result of the Jet. Another indication of RaCy!

In the afternoon of 18th Novemeber the severe development has started. A Dry intrusion runs into the depression. Over the highlands of Scotland some L mark the lee clouds. This development of the RaCy continues.
At 19th November 09UTC something very interesting can be observed as was before already mentioned sevral times in this case, namely the second development just south of the Alps. In the image we see this areaa marked with DI for dry intrusion. In the cold air behinf the RaCy some Cbs have developed over.