ETT Model Fields - 12 UTC 6 August 2004

Isentropes
The isentropes θe show isentropic up gliding to the northwest of the system with increasing stability, as values increase with height. To the southeast of the system we can see increasing instability at lower 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 higher than the IR values which indicates that there is at this time limited intrusion of drier stratospheric air around the system.

The VCS was laid from position A to B.

Convergence/Divergence:
The field of divergence shows convergence within the area of the Warm Front inclined crowding zone and within the lower part of the leading area of the isentropic trough configuration. In the upper part divergence prevails. The zero line of divergence is found close to the trough axis.

Isotachs
The Isotachs fields show a maximum of velocity at mid levels to the rear of the system of approximately 25 m/s (50 KT). The Jet stream is shown to the north with speeds of approximately 60 m/s (120 KT)

Vertical motion (omega):
Within the area of occlusion most upward motion is found. Typically the strongest upward motion is found at mid-levels.

Potential Vorticity:
The signal of potential vorticity is according to the WV-signal. At this stage no distinct deepening of stratospheric air can be observed .

Vorticity advection:
PVA is found within the whole area of the Occlusion. A PVA maximum exists within the Warm Front inclined crowding zone in the lower levels of the troposphere at approximately 700 hPa. This maximum is connected with the already pronounced cyclonic circulation in these levels.

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.

Temperature advection:
WA is found throughout the whole troposphere with maxima found in the center of the isentropic trough, as is typical for occlusions.