South Pacific Convergence Zone: A conduit for energy transport from the tropics to higher latitudes?

During austral summer, convection extends southeastward from the tropical West Pacific warm pool in a diagonal band towards Southern Hemisphere higher latitudes. The region of storminess is referred to as the South Pacific Convergence Zone (SPCZ). While similar diagonal cloud zones also exist in the South Indian and Atlantic basins, analogous Northern Hemisphere convective bands are not observed. Our previous work, using observations and a series of numerical experiments, found that basin-scale surface heating gradients, and the accompanying upper-troposphere zonal wind basic state, are conducive to accumulation of mid-latitude disturbances near these Southern Hemisphere cloud bands. While a climatology map of convection appears to join the tropics to the mid-latitudes, it is unclear whether the two regions are linked dynamically.

We explore three avenues for explaining intensity and orientation of the SPCZ: 1) Mid-latitude synoptic disturbances slow and wave energy density increases; 2) Tropical disturbances sometimes propagate from the warm pool region towards higher latitudes; 3) And, connections between tropical convection and mid-latitude cyclones are observed on slower timescales (e.g., MJO teleconnections). Each mechanism enhances the diagonal SPCZ because the zonal wind basic state is conducive for either the accumulation (1), or emanation (2 and 3), of wave energy. It is likely that teleconnections between the tropics and mid-latitudes occur via high frequency mechanisms (i.e., synoptic disturbances) embedded in the slower varying basic state. The bridge between high and low frequency variability poses a question of whether changing background SSTs associated with different phases and varieties of ENSO may influence not only where convection is likely, but also how wave energy is transported to different latitudes.