Wave Patterns and Southern Hemisphere Convergence Zones

Data from satellites and reanalysis products are analyzed to study the behavior of wave trains in the three major Southern Hemisphere Convergences zones: the South Pacific, the South Atlantic, and the South Indian. Using composites on high rain-rate days, a wave pattern is identified that is characteristic of high rain events. This wave pattern is then compared to the patterns of variability of brightness temperature using empirical orthogonal functions. A linear regression technique is used to examine the behavior of potential vorticity corresponding to the patterns of maximum variance. Planetary-scale waves, propagating in favorable regions, slow and break, dragging streamers of moisture from the tropics into higher latitudes. These streamers, combined with lifting, lead to the enhanced rain seen in the Southern Hemisphere?s convergence zones. It is concluded that the convergence zones are areas of enhanced streamer activity and that a more thorough study of streamers will yield more information on the structure and behavior of the convergence zones.