The formation of surface circulation systems

(Bluestein, pp. 213-214)

Given an upper-level, positive PV anomaly is advected over a zone of strong, low-level, north-south horizontal temperature

gradient:

• As for an upper-trough moving over a zonally-oriented surface cold front

• The anomaly induces a cyclonic vortex down to the frontal zone

• Warm advection occurs east of the induce surface cyclone, with cold advection occurring to the west of the induced cyclone (see Fig. 1.159)

The application of PV inversion to the problem of cyclogenesis (Hoskins et al.

1985)

There is a warm temperature anomaly to the east of the surface cyclone, and a cold anomaly to the west of the cyclone

The combined effect of these two induced vortices is a strong northerly wind component in the upper positive PV anomaly, and it is intensifying.

Therefore, the wave aloft grows in amplitude

Additionally, its eastward movement is slowed, since the PV contours just to the west of the anomaly are advected southward, and the PV contours east of the anomaly are advected northward.

This makes for an even stronger induced flow below, which in turn amplifies the upper wave, etc….rapid cyclogenesis!

Process is the same as that previously discussed for isobaric,

quasi-geostrophic theory:

In QG theory, surface cyclogenesis occurs when an upper-level trough moves over a low-level baroclinic zone

However, in PV thinking, we do not need to consider omega explicitly, as we do in QG thinking.