Understanding the Waviness of Extratropical Large-scale Atmospheric Circulation
Large meridional meandering of extratropical atmospheric circulation is conducive to blocking, persistent trough, and associated weather extremes. While the waviness of atmospheric circulation is often measured geometrically, the underlying dynamical mechanisms are still not well understood. I will present some recent results using local wave activity to quantify jet meandering, atmospheric rivers associated with Rossby wave breaking. Next, I will explain the physical basis of the circulation waviness from the perspective of large-scale atmospheric transport and mixing. It is shown that the waviness of extratropical atmospheric circulation can be understood largely by the spectral density of Rossby wave that has the same phase speed as the time mean zonal flow, analogous to the critical latitude theory of Rossby wave. This theory suggests that both weakened zonal wind speed and increased wave stirring would favor more circulation waviness, with zonal wind being the leading factor for the interannual variability in circulation waviness in the observations.