In this talk, we introduce a nonlinear multi-scale interaction (NMI) model of atmospheric blocking. Based on the NMI model, we propose a meridional background potential vorticity gradient (PVy) as a bridge from climate variability to weather extremes because the climate variability such as Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO) and so on (≥10 years) has much slower timescales than those of weather extremes (≤30 days), because weather extremes are mainly associated with atmospheric blocking events with timescales of 10-20 days. In our presentation, climate variability is considered as being able to change PVy through altering background atmospheric stratification, zonal wind and meridional temperature gradient. In this NMI model, PVy is a key factor determining the spatiotemporal evolution of atmospheric blocking, whereas the zonal movement of atmospheric blocking is mainly related to the magnitude of PVy, basic zonal wind strength and the blocking amplitude. When PVy is smaller, atmospheric blocking can have longer lifetime, larger zonal scale, less eastward movement and slower decay, thus favoring intense, widespread and long-lasting weather extremes in mid-high latitudes. In contrast, when PVy caused by climate variability is much smaller and below a threshold, atmospheric blocking will have shorter lifetime, smaller zonal scale, stronger eastward movement and faster decay, thus suppressing weather extremes. Thus, the NMI model is a useful tool for examining how climate variability influences extreme weather events.

blocking, weather extreme, multi-scale interaction