On Storm Tracks, Weather Regimes, and a Wave Breaking Recipe

Abstract

The mid-latitude atmospheric circulation is often described as a combination of low-frequency variability, such as weather regimes (WRs) that can persist for weeks, and high-frequency variability, including synoptic systems that shape our daily weather. In the North Atlantic, regimes such as the North Atlantic Oscillation influence the jet stream and affect surface climate. Here we investigate the dynamics governing the interaction between these timescales, and how it is mediated by Rossby Wave Breaking (RWB) events. A simplified equation is derived to explore which processes contribute to RWB through a meridional overturning of high-frequency potential vorticity, providing a dynamical recipe for when and where wave breaking occurs. We show that slowly varying regimes steer the tracks of high-frequency systems, which in turn determine whether the frequency of cyclonic or anticyclonic RWB is enhanced or suppressed. The recurrence of same-type RWB in a similar position can ultimately shape the mean structure of WRs. By linking the structure of WRs to the dynamics of wave breaking, our framework provides a dynamical basis for interpreting variability in midlatitude circulation.