On storm tracks, weather regimes, and a wave breaking recipe

The atmospheric circulation is often decomposed into high- and low- frequency variability. For example, the low-frequency variability in the North-Atlantic includes slowly varying weather regimes such as the North Atlantic Oscillation, with timescales of weeks. The high frequency variability includes the synoptic weather systems, which shape our daily weather fluctuations. The interaction among these timescales is often mediated by Rossby Wave Breaking (RWB) events, which involve the irreversible breaking and dissipation of the baroclinic waves. To investigate this interaction, a simple RWB recipe is derived by exploring which processes contribute to a meridional overturning of high-frequency PV contours. A picture emerges in which the slowly-varying weather regimes influence the tracks of high-frequency systems, which in turn, depending on the position relative to the low-frequency flow, determines whether the frequency of RWB (cyclonic or anticyclonic) is enhanced or suppressed. The recurrence of same-type RWB in a similar position then shapes the overall mean structure of the weather regime.