Author
Vesa Nietosvaara - FMIAlessandro Chiariello - FMI
Introduction
This short case study aims at illustrating, how the satellite imagery can be used to infer the qualitative structure of the wind field in the medium and low troposphere. Moreover the different skill of some RGB composites is highlighted in connection with the detection of the clouds properties at different altitudes.The case in question refers to the weather situation of September 19, 2007, when an extensive and compact cloud pattern is observed over the Adriatic side of the Appenninean mountain chain, stretching from the region of Emilia Romagna southwards until the northern part of Puglia.
 
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Left: "High Resolution Visible" RGB - 19 September 2007:1115 UTC. Right: Winds from Zadar sounding 19 September 2007 12 UTC.The location of Zadar sounding station is marked with red star. |
The motivation for the case study
The event itself caught the attention because at a very first glance the interpretation of the satellite imagery, in the light of conceptual models, led to apparent contradiction to what is explained in manuals:- The structure of low-level cloudiness east of the Apennine mountains, characterized by the sharp edge, appears to be Barrage (Stau) cloud.
- With the aid of image animations, the upper level cloudiness (Cirrus) is clearly moving from west to east, not from east to west as one would expect in the case of standard Barrage cloudiness case; for a standard Barrage cloud case the winds would be mainly from the same direction throughout the troposphere, which is obviouslyy not the case here.
- The cloud features seen in the satellite images can better be understood by investigating more thoroughly the wind at different heights and using RGB images to help the analysis of the upper and lower clouds.
The development of this event is shown with the help of several MSG channels. The mini case studie is further supplemented with a chapter "interactive overlays". In this chapter you can yourself overlay various numerical parameters on the corresponding satellite imagery. Through this interactive way you can reconstruct the case and exercise with it. The case was proposed by Finnish Meteorological Institute and ENAV - Società Nazionale per L'Assistenza al Volo (Italian Company for Air Navigation Services). If you think you can contribute to this case or to EUMeTrain by providing us dates of interesting case studies which happened in your region of interest, we encourage you to please write us using the above e-mail address.
Synoptic situation
Synoptic analysis for September 19th 2007 12 UTC
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IR Imagery (Meteosat 9 channel 10.8): time sequence (00-23 UTC)
This chapter shows and briefly describes the development in a sequence of hourly images.
WV Imagery (Meteosat 9 channel 6.2): time sequence (00-23 UTC)
In the following chapter the cloud configurations can be better related to the upper level dynamics using Meteosat 9 - WV6.2 channel.
Meteosat 9 - Airmass RGB: time sequence (00-23 UTC)
The development and especially the physical background is shown using the Airmass-RGB.
Meteosat 9 - 1.6+HRV+HRV RGB: time sequence (06-16 UTC)
The High resolution Visible RGB combined with 1.6 micron information (water and ice phase of clouds) gives better view into the phase of lower and upper clouds.
Meteosat 9 - WV6.2+WV7.3+HRV RGB: time sequence (06-16 UTC)
This rather unusual RGB images gives the best view into the flow at upper levels and at the same time the lower level clouds are seen well in HRV channel.