Cross-Equatorial Interactions during Tropical Cyclogenesis

This paper presents evidence that winter hemisphere events influence the genesis of tropical cyclones in the summer hemisphere equatorial trough. A rawinsonde composite technique is used to study the large-scale flow prior to cyclone development. This is compared with a composite of the flow during "quiet" or "nontropical cyclone" periods. The composites span the equator so that changes can be monitored in the winter hemisphere flow and in cross-equatorial effects. The composite analyses correspond well to the results of case study and time series analyses presented in a companion paper. On the basis of these results, an idealized scenario of the important synoptic events leading to cyclogenesis in the equatorial trough is described.