ETT Model Fields 1800 UTC 07/08/2004

Isentropes
The isentropes θe show increasing mid-level instability to the northwest of the system. Within the main cloud band we see isentropic stable profiles. Within the cloud head we observe increasing instability at low levels extending to mid-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 lower than the IR values to the northwest of the system, this signal implies that no dry air is present at high levels in this area. We see lower WV values within the remainder of the cross sectional area, signifying an intrusion of drier stratospheric air especially within the hook of the storm.

The VCS was laid from position A to B.

Convergence/Divergence:
The field of divergence shows convergence throughout the atmosphere ahead of the trough with areas of descent occurring at higher levels coincident and ahead of the trough.

The peaks of convergence are coincident with the frontal band and cloud head zones.

Isotachs
The Isotachs fields show a maximum of velocity at mid to lower levels approximately 28 m/s (60 KT). A further maximum is seen coincident with the hook of the development to the east of the center, this configuration and location is indicative of a sting jet decreasing to approximately 18 m/s 35 KT to the west of the center. The Jet stream is shown to the north with speeds of approximately 28 m/s (60 KT).

Vertical motion (omega):
Mass ascent is occurring throughout the atmosphere directly ahead of the trough with descent occurring to the the rear. The zero line of Ω marks the frontal boundary and trough axis.

Potential Vorticity:
The dynamic tropopause marked by PV=2 has descending behind the trough and both the WV and IR images show significant dips coincident with this feature. Dry descending stratospheric air with high PV values has descended to very low levels within the area of clear air close to the hook of the cyclone.

Vorticity advection:
A PVA maximum exists close to the trough.

Relative humidity
A maximum of relative humidity is found within the developing system.

Temperature advection:
WA is found throughout the whole troposphere ahead of the frontal zones, coincident with the maximum of Ω. Significant cold advection is also apparent to the area with the zero of advection marking the cold frontal boundaries.