Satellite images and derived numerical parameters
In the previous chapter, the recognition of a pre-existing baroclinic zone was made. Furthermore an upper level
feature in the WV-imagery could be clearly seen which was presumed to be the Upper-level PV anomaly. In this chapter
these significant features will be thoroughly investigated by use of derived numerical parameters.
Parameters which are helpful in the diagnosis of these features are:
- Geopotential height at 300/500 hPa, to find the upper level trough.
- Height of the PV=2 unit for finding the upper-level PV-anomaly
- ThetaW at 850 hPa for finding the low-level baroclinic zone.
- Isotachs 300 hPa to look for possible jet-interaction.
Geop. Height 300 hPa
In the following sequence the development of the upper-level trough can be seen very nicely.
Clearly a developing diffluent trough can be seen which at first shows some eastward propagation (From
the east-part of Greenland moving to Iceland). Quite soon the trough is standing still, but deepening
and forming a cut-off low.
The fields of geopotential height at 300 hPa are displayed in a 6-hourly sequence from 16 Oct 12 UTC - 19 Oct 18 UTC.
Height of PV=2
In the following sequence the existence of the Upper PV-anomaly can be clearly seen. This was already expected
after seeing the WV-imagery in the previous chapter. A distinct lowering of the tropopause height can be seen, especially
near the core of the cyclone indicating a distinct dry intrusion of stratospheric air moving into the upper and
middle levels of the troposphere.
The fields of the height of PV=2 are displayed in a 6-hourly sequence from 16 Oct 12 UTC - 19 Oct 18 UTC.
ThetaW 850 hPa
Initially only a weak occlusion can be detected when examining this field. The sequence clearly shows a
tightening gradient indicating an increase of baroclinicity. Later on in the sequence the straight gradient
starts to wave, indicating the cyclogenesis proces.
The fields of the height of ThetaW 850 hPa are displayed in a 6-hourly sequence from 16 Oct 12 UTC - 19 Oct 18 UTC.
Isotachs 300 hPa
In this sequence it can be seen that at the west-side of the diffluent upper trough a strong North-South
oriented jet develops. A small branch of this large jet-stream is pointed towards the area of development.
The developing cyclone is oriented at the left-exit region of this branch and at the right entrance region
of a SW-NE oriented jet-streak at the other side of the trough.
The fields of the Isotachs at 300 hPa are displayed in a 6-hourly sequence from 16 Oct 12 UTC - 19 Oct 18 UTC.
Geop. Height 500 hPa
In the following sequence de development of the upper-level trough can be seen very nicely the fields are comparable
to the 300 hPa height field. Clearly a developing diffluent trough can be seen which at first shows some eastward propagation (From
the east-part of Greenland moving to Iceland). Quite soon the trough is standing still, but deepening
and forming a cut-off low.
The fields of geopotential height at 500 hPa are displayed in a 6-hourly sequence from 16 Oct 12 UTC - 19 Oct 18 UTC.
Summary of the investigations in this chapter
In the sequences it was very clearly seen that a process of rapid cyclogenesis was going on. The
typical characteristics
of this cyclogenesis events were:
- Existence of an upper level PV-anomaly, related to a pronounced upper level trough.
- Existence of a low-level baroclinic zone.
- Interaction between item 1 and 2.
- Appearance of a wave-structure in the frontal cloud band.
- Appearance of a dry intrusion, related to the upper-PV anomaly.
- Development of a strong surface cyclone with a strong surface windfield.
Atypical aspects of this cyclogenesis event were.
- The upper level PV-anomaly and related upper level trough are stationary during the cyclogenesis process.
- The surface cyclone shows hardly no displacement and even retrogrades at the end.