Abstract:

The mid-latitude atmospheric circulation is often described as a combination of low-frequency variability, such as weather regimes 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. A key process by which the low and high frequency components of the flow interact is Rossby Wave Breaking (RWB), which occurs when large meanders in the jet stream, manifest as undulating potential vorticity (PV) contours overturn and break apart.  

In this study, we examine key parts of this multiple-time-scale interaction, by analyzing 35 years of atmospheric data, with a focus on understanding the distribution of  Rossby wave breaking, and how it links storms with weather regimes. Using a simplified equation for the evolution of meridional PV gradients in terms of low and high frequency flow components we are able to come up with a “dynamical recipe” for when and where wave cyclonic and anticyclonic wave breaking occurs. The mechanistic picture that emerges is that weather regimes steer storm tracks, which in turn, determine the type and location of wave breaking given the weather-regime flow. By linking the structure of weather regimes to the dynamics of wave breaking, our frame work provides a dynamical basis for interpreting variability in midlatitude circulation.