Vorticity describes the rotation of a flow field and is, therefore, as divergence a property of the flow field.

> 0 Cyclonic rotation
< 0 Anticyclonic rotation

PVA Positive Vorticity Advection
NVA Negative Vorticity Advection

There is a contribution to upward motion where term (1) of the omega equation is characterized by vertically increasing values of vorticity advection. (compare Vertical Motion - Omega Equation ).

This is fulfilled where PVA increases with height or NVA decreases with height. From the synoptic point of view, the first condition is much more interesting than the second because the main cloud configurations are associated with PVA rather than NVA.

In satellite meteorology a simplification of this rule has to be used because, within an evaluation system based on single isobaric surfaces, a vertical variation of a parameter like PVA cannot be detected so obviously. Consequently the distinct PVA maxima at 500 and/or 300 hPa are used directly instead of their vertical variation. This is only possible under the assumption that wind increases with height. Although this is a reasonable assumption one has to bear in mind that it is not fulfilled everywhere and everytime. Nevertheless, satellite meteorology has proved that this is a valuable method and guides an evaluator to look into the main maxima in the numerical vorticity advection charts at higher levels.

Typical cloud configurations which are completely or partly associated with this parameter are:

Some practical examples can be found in the case from 11 February 1997/06.00 UTC.

11 February 1997/06.00 UTC - Meteosat IR image; SatRep overlay: names of conceptual models
11 February 1997/06.00 UTC - Meteosat IR image; cyan: height contours 500 hPa
As vorticity is a property of the stream flow, namely the amount of rotation, a short overview of the height field at 500 hPa is presented. The following structures can be summarized:
11 February 1997/06.00 UTC - Meteosat IR image; cyan: height contours 500 hPa, magenta: relative vorticity 500 hPa
The combination of upper level height and vorticity fields shows the following typical relations described below. A discusion of the relationship between typical vorticity features and typical cloudiness can be found in chapter Development of Vorticity in which cloud forming parameters are discussed in more detail.

The following cyclonic vorticity maxima can be recognized:

11 February 1997/06.00 UTC - Meteosat IR image; magenta: relative vorticity 500 hPa, green: positive vorticity advection (PVA) 500 hPa
This image shows vorticity and the positive part of vorticity advection which is the important contribution for upward motion.

Two relationships will be discussed:

The following interesting situations can be extracted:

In this chapter the maxima of vorticity have been studied and compared to the PVA maxima; in the following chapter a further separation of the vorticity maxima together with a deeper interpretation of PVA maxima will be shown.