A New Look at Deformation as a Diagnostic for Large-Scale Flow

Abstract

eformation plays a key role in atmospheric dynamics because it provides a dynamical measure of the interaction between different scales, such as in frontogenesis. A climatology of deformation constructed from Interim ECMWF Re-Analysis (ERA-Interim) data (1979?2013) reveals four main processes associated with deformation: 1) frontogenesis at lower levels, 2) movement and evolution of jet streams in the upper troposphere, 3) orographic blocking, and 4) Rossby wave breaking. The merits of deformation as an additional perspective are discussed for these processes on the basis of case studies and composite analyses in conjunction with analytic solutions.This study shows that deformation can be used to unambiguously detect orographic blocking through the local strength of the flow diversion around orography. Moreover, the deformation signature for orographic blocking observed in case studies and composites closely resembles the analytic solution for two-dimensional flow around an obstacle.The climatology also reveals that Rossby wave breaking is associated with a characteristic ?-shaped deformation maximum. A composite analysis of this process confirms previous findings that suggested a dynamic link between Rossby wave breaking and dynamic blocking. It is shown that the deformation associated with Rossby wave breaking is aligned with the observed mean deformation upstream and downstream of a blocking high. Therefore, the presented composites illustrate a potential mechanism pinpointing how Rossby wave breaking can act to reinforce the flow diversion around the block.