TFP, RTP and WA

1st March 2004: 00UTC
In the image three different derived parameters are pictured. In blue the thermal front parameter (TFP), in red the warm air advection (WA) and in green the relative topography or equivalent thickness (RTP).
There are two different cloud phenomena of interest:

1. The cloud band extending along 70 N southeastward to the Norwegian coast.
2. The area to the north where in the cold air the first signs for the comma cloud can be recognised.

The cloud band shows frontal character supported by a high gradient of thickness, the zeroline of TA close to the rearward edge of the and some indication of a TFP within the cloud band.

The cloud area to the north is within a thickness ridge and WA at the boundary to a distinct CA center. From these parameter distributions it can be concluded that the initial stage of the cloud spiral under investigation is within a complete different physical state of the troposphere than the cloud band to the south. There are no frontal conditions in the area of the comma at the time being. The big cloud field can be called cloudness in the thickness ridge. This can be seen much better in a parameterfield (not shown here) of equivalent potential temperature at 850 hPa. This supports the idea that the wide spread cloud field is driven by the lower layers.

1st March 2004: 06UTC
The situation is quite similar to the one 6 hours before. The frontal character of the cloud band can be seen in the relevant parameters and the cloud system developing into the cloud spiral under investigation is in the cold ait trough at the boundary to an intensive CA maximum. One additional, new point is of interest namely a newly developed WA maximum along (approx. 70N05W); it reaches into the cold air area behind the frontal cloud band and might be an indication for a cyclonic rotation going on in this area.

1st March 2004: 12UTC
The frontal character of the cloud band is still evident but the distribution of TA maxima and minima disturb the classical configuration of TA along a front. On the other hand are the two WA and CA maxima a sign of a development going on at the cloud side behind the frontal cloud band. Cyclonic rotation might be the reason for the development of the two TA maxima and thus accompany the intensive development which is the subject of this case study.

1st March 2004: 18UTC
The frontal character of the cloud band is not longer well developed. But the comma feature which is now already well developed west of Norway is situated within a thickness trough representing cold air. CA is very intensive in front as well as behind the comma. But there is an intersection of a WA maximum which is – as already described in the 12 hours before – a sign for an intensive cyclonic rotation. This rotation is supported by the low center in surface and higher levels.

2nd March 2004: 00UTC
The rest of the cloud band followed during the previous day does now no longer show frontal characteristics, it has dissolved. The comma which has now moved to Sweden is still at the leading edge of a thickness trough and is accompanied by WA and CA maxima within and behind the cloud structure. Although there are some small indications of TFP, there is not yet a distinct frontal character contained in the parameters.

2nd March 2004: 06UTC
During the last 6 hours the characteristic features of the thickness trough and the TFP have increased. At the same time also the frontal cloud band has intensified; so the process of frontogenesis is somewhat reflected in the parameter fields characterising a frontal cloud band.

2nd March 2004: 12UTC
The statements made for 6 hours before are now not only further relevant but have even increased. The most important features are the development of a TFP branch and the WA maximum which followes the configuration of the spiral. The latter indicates not only the cyclonic rotation but also gives the impression of a occlusion spiral. However this is not a reflection of a classical occlusion process, but an indication to an intensive cyclonic rotation.

2nd March 2004: 18UTC
The same statements given for 6 hours before are also true for this point of time. The most dramatic change is the sharpening of the thickness trough.

3rd March 2004: 00UTC
The statements given before are also true further. In this last stage shown in the case study there is some frontal character of the synoptic scale cloud spiral. The relation to the thickness field is more that of an occluded cloud band.