Abstract

The Finite-Amplitude Rossby Wave Activity (FAWA) formalism has been developed by Nakamura and collaborators since 2010. Not only does FAWA satisfy the exact nonacceleration relation, but it also allows a precise partition of FAWA tendency into advection, mixing (in terms of effective diffusivity) and forcing. Various studies applied this theory to identify factors that govern the eddy-mean flow interactions at midlatitudes in both general circulation models and reanalysis data. Recently, Huang and Nakamura (2016) generalized FAWA into a longitudinally local wave activity (LWA). As LWA quantifies waviness of potential vorticity (PV) contour at each longitude and satisfies an approximate local non-acceleration relation, it is a suitable candidate to diagnose localized phenomena such as atmospheric blocking.

In this presentation, I will first give a brief historical account of the development of finite-amplitude Rossby wave theory (i.e. previous work by Andrews, Haynes, Killworth, Shepherd and McIntyre) and how our LWA formalism incorporates these ideas. I will then review the (zonal mean) FAWA formalism and its application. Furthermore, I will outline our LWA formalism and demonstrate with reanalysis data how LWA captures the climatology of blocking and describes the life cycles of blocking episodes.