Introduction
Vorticity patterns control the circulation of air masses in their vicinity. By doing this they control the location of important meteorological quantities that are essential for an accurate diagnosis and forecast of the atmosphere.
The scale of vorticity patterns in the atmosphere ranges from large-scale synoptic system circulations (low and high pressure centres) to smaller meso-scale circulations (water vapour vortices (sometimes referred as WV eddies or WV eyes). The (anti-)cyclonic rotation in the atmosphere caused by a vorticity maxima is easily seen in satellite imagery. And quite naturally, satellite imagery is the key tool to correctly locate the maximum of cyclonic and anticyclonic vorticity in the atmosphere. Moreover, satellite images are able to show the small-scale vorticity patterns that are easily overlooked and smoothed out by a NWP model. An example of this you see in the satellite images below where a range of small scale eddies resulting from a shear zone over the Atlantic Ocean were not recognised by the ECMWF model.
![Meteosat 9 WV image compared to ECMWF synthetic water vapor](media/graphics/meteosat_vs_ecmwf.jpg)
This training module has been developed to teach you to identify these vorticity centres in Meteosat Second Generation (MSG) satellite imagery. In addition the module will provide you with a firm physical background to help you understand why it is important to do a good diagnosis of satellite images and also provide you with a range of examples and exercises to demonstrate the impact a vorticity centre may have on your weather forecast.
To help refresh your memory, this first chapter will continue by presenting you the basics of vorticity by answering the question on "What is vorticity?". If you would already know the answer to this question you may choose to continue to chapter two on vorticity maxima.