Abstract/Summary

Barotropic variability plays an important role in a variety of extratropical atmospheric processes, such as annular modes, teleconnections, and baroclinic life cycles, which occur on a wide range of timescales. Extratropical dynamics is dominated by high-frequency (periods shorter than 10 days) transient waves, which drive barotropic variability through baroclinic life cycle events. However, other types of waves (e.g. low-frequency, with periods longer than 10 days, and stationary waves) also play an important role in shaping extratropical dynamics on various timescales. This study uses reanalysis data in the context of the zonal momentum budget to address the relative importance of stationary, low-frequency and high-frequency waves in driving barotropic variability at high (synoptic) and low (subseasonal-to-seasonal) frequencies both locally in storm track regions and in the zonal mean in both hemispheres. The analysis reveals that the eddy forcing of barotropic variability on synoptic timescales is dominated by the interaction between low-frequency (and stationary) and high-frequency waves, and not by high-frequency self-interactions. On longer (subseasonal-to-seasonal) timescales the picture is more complex, with increased importance of low-frequency self-interactions but still largely negligible high-frequency self-interactions. A better understanding of the mechanisms driving barotropic variability on subseasonal-to-seasonal timescales may help advancing predictability on these timescales.