Dynamics of the Land-based Convergence Zones of the Southern Hemisphere

Three convergence zones are prominent in the summertime climatology of the Southern Hemisphere. The SPCZ emanates eastward/southeastward from the western Pacific warm pool. The SACZ and the SICZ stretch southeastward from South America and southern Africa, respectively, and are marked by high precipitation rates that are dynamically supported by both convergence and moisture advection. These two land-based convergence zones (LBCZs) are fundamentally related to the juxtaposition of the continental heat lows and the subtropical highs to their east/southeast. The strength, positioning, and variability of the LBCZs can be understood by considering how the thermal lows and subtropical highs are established.

LBCZs are regions of strong transient eddy activity and interactions across space scales. Along with the SPCZ, they are major conduits for heat and momentum fluxes between the tropics and extratropics.. The SICZ and, to a lesser extent, the SACZ have preferred positions, and these lead to a northeast/southwest dipole signal in the observed precipitation field. The idea that the preferred positioning of the convergence zones acts as a "switching" mechanism, regulating the flow of heat and momentum into middle latitudes, is explored.