Intraseasonal periodicity in the Southern Hemisphere circulation on regional spatial scales

Journal of Atmospheric Science | Thompson et al. [2017]

Abstract

Wave activity in the Southern Hemisphere extratropical atmosphere exhibits robust periodicity on timescales of ~20-25 days. Previous studies have demonstrated the robustness of the periodicity in hemispheric-averages of various eddy quantities. Here the authors explore the signature of the periodicity on regional spatial scales.

Intraseasonal periodicity in the Southern Hemisphere circulation derives from out-of-phase anomalies in wave activity that form in association with extratropical wave packets as they propagate to the east. In the upper troposphere, the out-of-phase anomalies in wave activity form not along the path of extratropical wave packets, but in their wake. The out-of-phase anomalies in wave activity gives rise to periodicity not only on hemispheric-scales, but also on synoptic scales when the circulation is sampled along an eastward path between ~5-15 m/s. It is argued that 1) periodicity in extratropical wave activity derives from two-way interactions between the heat fluxes and baroclinicity in the lower troposphere; and 2) the unique longitude/time structure of the periodicity in upper tropospheric wave activity derives from the contrasting eastward speeds of the source of the periodicity in the lower troposphere (~10 m/s) and wave packets in the upper troposphere (~25 m/s).

*Full text can be found [here](http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-16-0094.1?af=R)*.

 

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