ETT Model Fields - 06 UTC 7 August 2004

Isentropes
The isentropes θe show increasing lower level instability to the northwest of the system. To the southwest we see very little change in the isentropes at low levels with some ridging now at higher levels.

Orange thin: IR pixel values

Orange thick: WV pixel values

The high values in the IR image are clearly reflected in the pixel values in this cross section. The values of WV are now lower than the IR values which now indicates that there is drier stratospheric air has now become to be engaged and drawn into the system.

The VCS was laid from position A to B.

Convergence/Divergence:
The field of divergence shows convergence within the warm front and warm sector of the developing system at with a maximum at low levels and ahead of the trough axis. Divergence is found at high levels.

Isotachs
The Isotachs parameters show that the strongest winds at low levels around the system are now approximately 14 m/s (28 KT) with the winder wind field to the rear and southwest of the system. The Jet stream has now decreased to approximately 40 m/s (80 KT)

Vertical motion (omega):
Mass ascent is occurring ahead of the trough with a maximum at mid to high levels.

Potential Vorticity:
We can know see that significant stratospheric air has been drawn down into the troposphere to the rear of the development, this is also signaled by the water vapour pixel values. the dynamic trop has a significant fall behind the trough, signaling deep penetration of cold air being drawn into the development.

Vorticity advection:
A maximum of positive vorticity advection is now occurring ahead of the trough. he maximum in upper levels is situated above the highest cloud part in the leading part of the cloud band. We also see slight NVA occurring ahead of the development, this corresponds with the upper ridge and right exit of the jet stream.

Relative humidity
A maximum of relative humidity is found within the developing system. Significantly drier polar air is seen to the rear on the development and is descending to lower levels.

Temperature advection:
Warm advection is taking place throughout the atmosphere ahead of the upper trough and ahead of the development. Significant cold advection is now occurring to the rear of the system indicating the position of the cold front and polar air. This system is now fully developed and has a marked baroclinicity.