Baroclinic instability and large-scale wave propagation on the planetary-scale atmosphere

by Dr Woosok Moon (Nordita)

Monday 8 Nov 2021, 15:45 → 17:45 Europe/Stockholm

Albano 3: 6228 - Mega (22 seats) (Albano Building 3)

Hybrid mode: 

zoom link : https://stockholmuniversity.zoom.us/j/622224375

Abstract:

Midlatitude atmospheric variability is dominated by the dynamics of the baroclinically unstable jet stream that meanders and sheds eddies at the scale of the Rossby deformation radius. The eddies interact with each other and with the jet, affecting the variability at a wide range of scales, but the mechanisms of planetary-scale fluctuations of the jet are not well understood. Here, we develop a theoretical framework to explore the stability of planetary-scale motions in an idealized two-layer model of the atmosphere. The model is based on a combination of the vertical shear and the Sverdrup relation, providing the dynamic link between the two layers, with meridional eddy heat fluxes parameterized as a diffusive process with the memory of past baroclinicity of the jet. We find that a planetary-scale instability exists if the vertical shear of the jet does not exceed a particular threshold. The inclusion of the eddy memory effect enables westward or eastward propagation of planetary waves relative to the barotropic mean flow. Importantly, we find growing planetary waves that propagate slowly westward or are stationary, which could have important implications for the formation of atmospheric blocking events. Our theoretical results suggest that with the ongoing polar amplification due to global warming and the corresponding reduction of the vertical shear of the mean wind, the background conditions for the growth of planetary-scale waves are becoming more favorable