The instability of Long's stationary solution and the evolution toward severe downslope windstorm flow. Part II: the application of finite-amplitude local wave-activity flow diagnostics

Abstract

An analysis of severe downslope windstorm evolution, from flow conditions initially described by Long's stationary solution, is considered through the application of finite-amplitude wave-activity diagnostics. Such quantities satisfy a local conservation law of the form At + ∇.F = 0. In particular, an analysis of the pseudo-energy density A and flux F is undertaken since the corresponding conservation law may be employed to describe disturbances to basic states that are nonparallel. In this study, such diagnostics are primarily enlisted to identify and chronicle the life cycle of normal-mode instability in the breakdown of Long's solution. It is concluded that the large-amplitude stationary disturbance, which defined the second stage of windstorm evolution in Part I of this study, was the result of a normal-mode instability of Long's solution. -from Authors