A Perspective on the Evolution of Atmospheric Blocking Theories: From Eddy-Mean flow Interaction to Nonlinear Multiscale Interaction

In this paper, we first review the research advancements in blocking dynamics and highlight the merits and drawbacks of the previous theories of atmospheric blocking. Then, the dynamical mechanisms of atmospheric blocking are presented based on a nonlinear multi-scale interaction (NMI) model. Previous studies suggested that the eddy deformation (e.g., eddy straining, wave breaking, and eddy merging) might lead to the formation and maintenance of atmospheric blocking. However, the results were speculative and problematic because the previous studies, based on the time-mean eddy-mean flow interaction model, cannot identify the causal relationship between the evolution of atmospheric blocking and the eddy deformation. Based on the NMI model, we indicate that the onset, growth, maintenance, and decay of atmospheric blocking is mainly produced by the spatiotemporal evolution of pre-existing upstream synoptic-scale eddies, whereas the eddy deformation is a concomitant phenomenon of the blocking formation. The lifetime of blocking is mainly determined by the meridional background potential vorticity gradient (PV_y) because a small PV_y favors weak energy dispersion and strong nonlinearity to sustain the blocking. But the zonal movement of atmospheric blocking is associated with the background westerly wind, PV_y, and the blocking amplitude. Using this NMI model, a bridge from the climate change to sub-seasonal atmospheric blocking and weather extremes might be established via examining the effect of climate change on PV_y. Thus, it is expected that using the NMI model to explore the dynamics of atmospheric blocking and its change is a new direction in the future.