A Nonlinear Multi-Scale Interaction Model for Atmospheric Blocking: A Tool for Exploring the Impact of Changing Climate on Mid-to-High Latitude Weather Extremes

A nonlinear multi-scale interaction (NMI) model was proposed and developed by the first author for nearly 30 years to represent the evolution of atmospheric blocking. In this review paper, we first review the creation and development of the NMI model and then emphasize that the NMI model represents a new tool for identifying the basic physics of how climate change influences mid-to-high latitude weather extremes. The building of the NMI model took place over three main periods. In the 1990s, a nonlinear Schrödinger (NLS) equation model was presented to describe atmospheric blocking as a wave packet; however, it could not depict the lifetime (10−20 days) of atmospheric blocking. In the 2000s, we proposed an NMI model of atmospheric blocking in a uniform basic flow by making a scale-separation assumption and deriving an eddy-forced NLS equation. This model succeeded in describing the life cycle of atmospheric blocking. In the 2020s, the NMI model was extended to include the impact of a changing climate mainly by altering the basic zonal winds and the magnitude of the meridional background potential vorticity gradient (PV_y). Model results show that when PV_y is smaller, blocking has a weaker dispersion and a stronger nonlinearity, so blocking can be more persistent and have a larger zonal scale and weaker eastward movement, thus favoring stronger weather extremes. However, when PV_y is much smaller and below a critical threshold under much stronger winter Arctic warming of global warming, atmospheric blocking becomes locally less persistent and shows a much stronger westward movement, which acts to inhibit local cold extremes. Such a case does not happen in summer under global warming because PV_y fails to fall below the critical threshold. Thus, our theory indicates that global warming can render summer-blocking anticyclones and mid-to-high latitude heatwaves more persistent, intense, and widespread.