An instability of mature cold fronts

Abstract

An instability of a cold front possessing a low-level warm-band precursor is examined within an f-plane, quasi- and semigeostrophic framework. The basic frontal state is taken to be two-dimensional and of uniform potential vorticity. Theoretical considerations pinpoint the source and nature of the instability to be a vortex interaction effect acting across the thermal maximum of the warm band. They also reveal that the most unstable mode associated with this flow configuration has a mixed barotrophic-baroclinic character and possesses some features (eg, a wavelength ~1000km and a doubling time ~1.5 days) that are akin to surface frontal waves. -from Authors