The typical satellite imagery features of this conceptual model can usually be seen only in the WV image; that means that this is a situation with little or no major cloudiness, but with distinct features in the water vapour field. Investigation of about 100 cases over a period of two years shows that a distinction can be made between different WV structures. The two prevailing structures are the so-called WV Eddies and WV Eyes.

Appearance in Meteosat imagery:

• WV Imagery:
  • Initial "old" Dark Stripe, associated with a former baroclinic zone. (compare Water Vapour Dark Stripes )
  • During development a cyclonic structure forms. In the case of an WV Eddy, air with a higher moisture content, spirals around drier air. In the case of a WV Eye, dry air is being surrounded by moist air and eventually a dark, round spot will be formed
• IR/VIS Imagery:
  • The main features of this conceptual model can only be seen in WV images. However, near the centre of a WV Eye cloud production can be suppressed, or clouds can dissolve.

The main differences between the WV Eye and WV Eddy can be seen in the satellite imagery and are summarised in the schematics above and in the table below.

WV Eddy	WV Eye
A mesoscale cyclonic spiral structure with wet and dry air masses forming the spiral	A dark, almost round spot which has been encapsulated by moister air.
Developing due to the deformation of one edge of the Dark Stripe (see schematics above)	Developing due to the deformation of both edges of the Dark Stripe (see schematics above)
Some small cloud cells may exist in the leading part of the wet air stream, close to the transition zone between the high and low WV values.	No convection occurs. Significant drying out of middle and upper levels of the troposphere and even dissipation of lower cloudiness (clear spells)
End stage: Filling with moist air due to convection	End stage: merging with other system, disturbed by mountains or disappearing by overrunning moist air
In some cases: a WV Eddy transforms into a WV Eye

Water Vapour Eddy

The WV images above show a developing WV Eddy in the bay of Biscay which is moving in a northerly direction. The WV Eddy is situated just ahead of a (cold) frontal cloud band. Furthermore the bright white spots within the spiral indicate that convection is present.
In the VIS and IR imagery below, there is no significant cloudiness. The only cloudiness that can be seen is Stratocumulus Sheets that have formed beneath a marked subsidence inversion. The distinct WV spiral can not be seen in these imagery. The location of the WV Eddy is indicated by the red arrow.

Water Vapour Eye

In the example below, starting on 10 October 2002, part of the life cycle of a WV - Eye can be seen over Norway, moving to Sweden: In the first image of the sequence, there is a clear initial Dark Stripe. In the following images, a dark round spot can be seen which is surrounded by moister air; this is the WV Eye. The loops below show a Water Vapour Eddy and a Water Vapour Eye.