CONICET | Buscador de Institutos y Recursos Humanos

Convectively coupled Kelvin waves over the South American continent are examined through the use oftemporal and spatial filtering of reanalysis, satellite, and gridded rainfall data. They are most prominent fromNovember to April, the season analyzed herein. The following two types of events are isolated: those thatresult from preexisting Kelvin waves over the eastern Pacific Ocean propagating into the continent, and thosethat apparently originate over Amazonia, forced by disturbances propagating equatorward from central andsouthern South America.The events with precursors in the Pacific are mainly upper-level disturbances, with almost no signal at thesurface. Those events with precursors over South America, on the other hand, originate as upper-levelsynoptic wave trains that pass over the continent and resemble the cold surges documented by Garreaudand Wallace. As the wave train propagates over the Andes, it induces a southerly low-level wind that advectscold air to the north. Precipitation associated with a cold front reaches the equator a few days later andsubsequently propagates eastward with the characteristics of a Kelvin wave. The structures of those wavesoriginating over the Pacific are quite similar to those originating over South America as they propagate toeastern South America and into the Atlantic.South America Kelvin waves that originate over neither the Pacific nor the midlatitudes of South Americacan also be identified. In a composite sense, these form over the eastern slope of the Andes Mountains, closeto the equator. There are also cases of cold surges that reach the equator yet do not form Kelvin waves.The interannual variability of the Pacific-originating events is related to sea surface temperatures in thecentraleastern Pacific Ocean. When equatorial oceanic conditions are warm, there tends to be an increase inthe number of disturbances that reach South America from the Pacific.

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