Height of PV = 2 units (Stratospheric Air) with WV Imagery

In the conceptual model of an instant occlusion PV=2 is not assumed as a key parameter. However, it can provide supporting information.

The broad dark area behind the cold front (between Iceland and Scotland) was already described in the WV image and airmass RGB chapters. It was interpreted as stratospheric dry air protruding down to lower levels. Compared with the models fields of PV=2 it gives an excellent fit.

The maximum of PV=2 and the dark area in the WV images moved to the Southeast. This clear PV anomaly was situated on the southern edge of the comma-like feature (near North Scotland).

The PV=2 maximum superimposed the convective zone near the trough axis (better to be seen in IR-images). It caused intensification finally yielding a comma.

Dry stratospheric air partially superimposed the comma and protruded downward, seen as darker areas in these parts of the comma.

As the situation developed, the comma intensified (brightening clouds over the Southern North Sea). A maximum of PV=2 is found south of the former comma reaching into the shallow moist zone between the spiral and the cold front. The maximum reached down to 600 hPa, which is an explanation of the rapid cyclogenesis and high wind speeds.

While the surface low remained nearly stationary over the next hours, maxima of PV=2 coincide well with the darker areas in the WV image.

The surface low changed its position only slightly. The PV=2 maxima coincide well with the darker areas in the WV image.

At the end of the life-cycle, stratospheric air indicated by a clear PV anomaly extended to the center of the occlusion spiral.

Maxima of PV=2 still coincide with the darker area in the WV image.