Barotropic instability in frontolytic strain

Recent observational studies have indicated that a front which is undergoing frontolytic strain may be conducive to rapid growth of waves or secondary cyclones. Previous work has shown that a frontogenetic strain flow will tend to suppress the growth of waves on a two‐dimensional vortex strip: here, the opposite case of negative strain is studied. Justification for considering a basic state which is frontolytic is presented, given the natural transience of this state. The results show that the growth is sufficiently rapid for instability to be relevant on the time‐scale of evolution of the parent front. Waves grow kinematically with the front itself, at an exponential rate. More rapid growth is possible for transient barotropically unstable modes but only for limited time. These results are discussed with a view to their impact on the understanding of atmospheric flows.