Wind in 300 hPa and airmass composite, Time Sequence: 3h, 29 February to 01 March 2008     

This chapter contains the combination of wind speeds in 300 hPa and the airmass composite (see legend).

We will investigate the positions of jet axis and corresponding dynamical processes The wind in 300 hPa represent normaly the jet axis quite well. Due to the vertical tilting of the jet axis some (small) deviations between the maximum model wind in 300 hPa and real jet axis may exist, despite some weaknesses in the model simulations. Regardless these possible problems, we will call the maximum wind in 300 hPa "jet axis" or "jet".

This image reveals over the Northwest Atlantic a strong jet with more than 200 kt wind speed that fits well with the long and line orientated transition from purple colour to blueish area. The surface low was situated at its left exit.

The jet intensified to wind speeds of more than 220 kt and the surface low remained at its left exit, i.e., under positive vorticity advection. The satellite image exhibits northeast of Ireland high extending clouds and a sharp transition to middle clouds where we find the jet axis that overrun the frontal cloud band in relation to the Warm Conveyer Belt. North of this transition we find PVA (left exit).

The jet extended more to southeast and a new maximum developed (marked by a white "+").

The jet extended in the meanwhile to England. The surface low and the split front were in its left exit.

The jet axis covered the entire Atlantic and arrived at the dutch coast. The strong convection over Scotland happened in its left exit.

The wind speed in 300 hPa over UK increased fast. We still see a good correspondence between the maximum wind and the transition from violet-purple to blueish areas of the air mass RGB

All systems moved to the East. A particular wind maximum can be seen over the Central North Sea.

Whereas the jet weakened over the Atlantic the wind speed increased over UK and Middle Europe. Strong positive vorticity advection occured over the southern North Sea (left exit with a strong gradient of wind speed).

The left exit arrived the southern North Sea. Due to PVA at its left exit and potential instability a convective line developed.

The convective line at the left exit of the jet is clearly to be seen.

The jet axis fits rather well with rear cold front's edge over Germany. At the jet's left exit the convective line reached higher intensities. (A further hint to its likely intensification comes from the pinkish colour that was caused by the high PV superimposing the compact clouds. Upward motion led partly to severe convection due to the lifting of the unstable air.

The situation did not change generally. We still find the convective line under the influence of approaching PV yielding PVA that is also indicated by the left exit of the jet.

Whereas a new wind maximum developed over East Austria the west parts of the convective line came under the jet axis yielding less PVA.

Thew west part of the convective line became weaker. Reasons for that are the loss of PVA because the cloud band was not longer at the left exit and orographic effects near the Alps. However, the part of the convective line over East Europe was still on the left exit and consequently influenced by PVA.

Convective line and cold front moved fast to Southeast.

The convective line moved to West Russia and the cold front arrived over the south of the Balcans.

The cold front and convecive line continued moving to southeast and east, respectively.