A theoretical and diagnostic study of solitary waves and atmospheric blocking

Abstract

Theories which associate atmospheric blocking with isolated "free mode' solutions of the equations of motion are reviewed and the central role played by the potential function Λ≡dq/dψ (where q is the quasi-geostrophic potential vorticity and ψ is the streamfunction) is emphasized. A diagnostic study of the European blocking episode during October 1987 is presented and the relationship between q and ψ investigated by plotting scatter diagrams of quasi- geostrophic potential vorticity against the streamfunction on an isobaric surface. An approximate functional relationship is found allowing Λ to be defined. The data strongly suggest that blocking episodes can exhibit local free-mode dynamics and that their persistence may in part be attributed to the robustness and stationary nature of these local coherent structures. -from Authors