A study of two cases of comma-cloud cyclogenesis using a semigeostrophic model

Abstract

It is found that for the comma clouds the instability is a baroclinic interaction of upper- and lower-level PV anomalies. However, heating is an important source of potential vorticity in these modes, and substantially influences their structure. This is reflected in a tendency for the surface depression to be confined to the heating region on the cold-air side of the jet, particularly in one of the cases where the surface temperature gradient was very weak. It also results in a shorter wavelength due to a reduced vertical scale as the midtropospheric PV anomaly associated with the upper part of the heating region becomes stronger than the anomaly produced at the PV gradient at the tropopause. -from Authors