The case study presents a classical development process of an instant occlusion. The merging of a comma-like cloud feature with a cold front can be clearly seen in IR images. Many derived parameters match the conceptual model of an instant occlusion very well. However, there are differences to an ideal case. Unusual seems a PV anomaly which superimposes the comma. Obviously, downward protruding dry air from the upper troposhere and lower stratosphere played a certain role and could have enforced the development.
The conceptual model of a comma explains the development of the enhaced cumuli to the comma-like cloud feature which takes place in the area of cold air behind the cold front in this case study. The comma is clearly superimposed by positive vorticity advection.
A cold air development describes the evolution of a comma to a cloud spiral in an area of cold air. No warm front is present during a development like this. This can be also observed in this case study but the cloud configuration and the derived parameters fit much better the conceptual model of an instant occlusion rather than a cold air development.
The classical polar front theory describes the life cycle of polar front cyclones. It has several limitations as many processes cannot be explained by this theory. The presented case is an example of a development which does not follow the life cycles stated by the polar front theory. The occlusion stadium is reached without a prior formation of a wave.
The rapid cyclogenesis during this time period shows a good correspondence to the Hoskins theory: The penetrating dry stratospheric air to lower parts of the troposphere can clearly be seen from the water vapour images. Vertical cross sections of PV reveal the approaching of PV anomaly in higher levels to a baroclinic zone in lower levels.