Zentralanstalt für Meteorologie und Geodynamik (ZAMG) - Austria
Satellite images have the big advantage of showing convective systems over their whole life time. Even though no precipitation can be observed during the earliest stages of a growing convective cell (e.g. weather radar or surface reports) the onset of deep convection can already be seen clearly in the water vapour images.
Looking at convective features in satellite imagery one interesting phenomenon can be recognised: preferred areas for the initiation of thunderstorms are located at the boundaries between moist and dry air in the water vapour images.
The synoptic environments for such situations can be distinguished:
• at the rear side of a frontal cloud band
• at the leading side of frontal cloud bands
• under fair weather conditions
On one hand those convective developments are driven by the different dynamical - physical processes described by potential vorticity, vorticity advection, temperature advection and frontal dynamics in general. On the other hand, they are influenced by the air mass qualities represented in the satellite water vapour image like humidity in upper layers as well as insolation leading to diabatic heating at the low levels of the troposphere.
Different occurrences can be derived from the investigations: Most of the cases show the first deep convective development at WV - boundaries, subsequent developments seem to take place within the wet areas. Only a few developments are situated completely within the dry water vapour stripes.
The different physical backgrounds will be described and probable areas for new development will be delimited with the help of the water vapour boundaries.