Local barotropic instability

Abstract

The more localized the jet is, the more dominant the stationary unstable mode would be. Our nonmodal analysis confirms that an isolated disturbance not only has to have a favorable orientation but also has to be in the downstream position with respect to the jet core before it can develop rapidly. Furthermore, a disturbance with a localized structure in the downstream region of the jet core can emerge from a zonally unbiased disturbance within a few days. The same mechanisms of local energetics account for the downstream localization of the disturbances during this transient adjustment as in the normal modes. The maximum instantaneous growth rate of such a nonmodal disturbance can be several times larger than that of the most unstable normal mode. -from Authors