On Conceptual Understanding of Blocking Dynamics and Baroclinic Annular Mode

Large-scale weather systems are building blocks of coherent modes of atmospheric variability in the mid-latitudes. The storm track has a periodic behavior on the timescale of 20-30 days (i.e., Baroclinic Annular Mode), whereas atmospheric blocking - the stagnation of the weather systems often last for 10-20 days. Both the periodic behavior of storm track and atmospheric blocking often cause weather extremes in the mid-latitudes. Yet, their first-order dynamics remain enigmatic, and they have been traditionally studied in separate subfields. In this report, I will show evidence that the evolution of coherent and propagating Rossby wave packets is instrumental to both Baroclinic Annular Mode and atmospheric blocking. Based on Rossby wave dynamics and quasi-geostrophic model, I will demonstrate a minimal conceptual model to capture both phenomena. I argue that the first-order dynamics of baroclinic annular mode and atmospheric blocking are due to an evolution of Rossby wave packets where constructive and destructive interference happens in different fashions. Their wave packet's properties dictate the corresponding timescales. I will use this conceptual model to explain the observed statistical relation between Baroclinic Annular Mode and atmospheric blocking in reanalysis products, idealized GCM, and climate models.