PV in 310 K and airmass composite, Time Sequence: 03h, 29 February to 01 March 2008     

In this chapter we consider the combination of airmass composite and the potential vorticity at the isentrope 310 Kelvin (roughly about 6 km high). This gives more understanding about the dynamical processes and how they were related to the cloud structures and airmasses gained from the airmass RGB.

South of Iceland we see the cloud head and the Warm Conveyer Belt in relation to the surface low. The airmass RGB exhibits violet/purple areas in connection to a PV-maximum. Further to the west we see a line-shaped transition of purple to blueish. Near the strong gradient of PV we have the frontal zone and the jet stream. (Because the jet and the frontal zone exhibits vertical tilting this can be used only as an estimation).

Unfortunately, no PV-fields are available for this time. However, we clearly see that the stratospheric air is overrunning the high extending and compact clouds south of Iceland.

The PV-field and the corresponding cloud structures moved to the east. We clearly see the overunning stratospheric air over the rear part of the cloud band (west of Scotland).

A particular PV-maximum can be found southeast of Iceland (marked by a white "+"). East of it convection took place (due to positive vorticity advection, PVA).

Although this is outside of our scope it is interesting to mention: Relatively low PV over the occlusion and the warm front. Because PV is the product of stability and absolute vorticity we find lower PV-values over the occlusion and the warm front because the air is not as stable as the stratospheric air. Where PV exhibits a strong gradient we find the warm front (however, in higher levels, here: North Sea, near the Cirrus shield of the warm front)

One PV-maximum moved near Scotland. Intense convection occured east and southeast of it.

The PV-maximum intensified an arrived North Scotland.

The overrunning stratospheric air is still clearly visible (Central North Sea to North Germany). High PV-values are very well connected to the pinkish, brownish areas. East of Scotland a new maximum developed (marked by a white "+").

This is the starting point of the convective line. The new PV-maximum moved from East Scotland to the Central North Sea. Due to PVA in its forefield the convective line developed.

The area of high PV (in relation to the violet/purple area) arrived the German coast of the North Sea. The convective line is totally superimposed by PV and laying in the forefield of the approaching PV-maxima.

The PV-maximum is just at the rear flank of the convective line. Over North Germany surface pressure tendencies up to -10 hPa/3h were measured and the lightning activity increased.

A particular PV-maximum arrived Northwest Germany. The entire convective cloud band was superimposed by PVA in front of the approaching PV-maximum and reached its maximum activity (line-orientated lightnings with high radar reflectivites (up to 50 dBz) and decreasing surface pressure in the convective line and rising surface pressure in its rear).

All structures moved fast to Southeast. The convective line was still influenced by PVA.

As already explained in other sub-chapters, the PV-maximum moved to the east. This is the explanations for the convective line's weakening in its west parts whereas the eastern parts still remained very active.

One PV-maximum arrived Slovakia causing more convection/thunderstorms at the convective line in this area. The west parts continued weakening due to the loss of dynamic forcings.

The convective line arrived Romania. We still find a PV-maximum (white "+") near-by.

The convective cloud band became less visible. It arrived at the Balcans.

The weakening of thunderstorm activity continued as indicated by the decreasing of lightning detection's density and increasing part of green symbols (lightning more than 20 minutes ago) in relation to other colours.

Lightning interval: