Low-Frequency Suppression of Tropospheric Eddy Heat Flux

In this presentation, we analyze the variability of Southern Hemisphere tropospheric eddy heat flux in reanalysis data. Consistent with previous studies, we find that eddy heat flux variability is weak at frequencies smaller than the 20-day peak associated with the baroclinic annular mode. We show that this spectral suppression largely arises from the anticorrelation in the eddy heat transports by different zonal wave numbers at low frequency (eddy heat transports by individual waves have red spectra and are not suppressed). Although the most plausible mechanism for this anticorrelation invokes baroclinicity as a mediating agent, this hypothesis does not seem to be supported by the observed low-frequency variability of baroclinicity. We test alternative hypotheses in simulations with an idealized model.