1st March 2004: 00UTC
There are at least two PV anomalies (stratospheric air has protruded downward into the tropsophere, consequently the height of PV = 1 unit is lower than approx. 500 hPa) in the nordic panel. The one is the center of the occlusion spiral over N-Sweden which is not considered in this case study. The second is along the rearward edge of the frontal cloud band but is not so intensive.
The area of interest where the cloud spiral of this case study develops, the cold air behind the frontal cloud band is not clearly diagnosable. It seems as if the isolines of height would “jump” down to the surface.
1st March 2004: 06UTC
For this point of time a distinct PV anomaly can already be recognised in the area of the developing cold air comma showing that there is a PV anomaly behind the cloud spiral. The downward protrusion of stratospheric air as well as the interaction with the tropospheric air can be followed much better in verticla cross sections which will be shown in a later chapter.
1st March 2004: 12UTC
The situation is the same as for 6 hours before and therefore all statements made there are valid here, too.
Several times the discrepancies of the intensive cyclonic development under discussion to other classical developments have been worked out. Also the configuration of this parameter shows discrepancies. During a classical occlusion process, the high values of PV develop only in the end phase; in this case they are already existing in the initial phase. PV anomalies in connection with rapid cyclogenesis development show also a different behaviour to this case because the important fact is an approach of a PV anomaly to a baroclicnic system while here it is already very close to the cloud feature from the very beginning on.
1st March 2004: 18UTC
The same statements are true as before.
2nd March 2004: 00UTC
Cyclogenesis or the deepening of dry stratospheric air is always accompanied by high values for PV. In this image this feature is well reflected. Within the cloud feature high values for PV can be found, a clear signal for cyclogenesis.
2nd March 2004: 06UTC
As the cloudspiral develops a strong signal in PV can still be observed.
2nd March 2004: 12UTC
The same statements are true as before. The developing cloud band coincides with a high gradient in the PV = 1 height. This is typical for a frontal cloud band.
2nd March 2004: 18UTC
Deepening up to 600 hPa. can be observed in the spiral. Indication of strong cyclogenesis.
3rd March 2004: 00UTC
The appearance of the clouds in IR imagery have weakened over the past six hours, which is also reflected by the decrease of PV within the cloud spiral (no further deepening/development).
