Teleconnections between the tropical Pacific and the Amundsen-Bellinghausens Sea: Role of the El Niño/Southern Oscillation

Tropical Pacific–high southern latitude teleconnections are shown to be caused by Rossby wave dynamics and are sensitive to the exact pattern of sea surface temperature (SST) anomalies forcing anomalous ascent. Further, the signal becomes obscured by local natural variability at higher southern latitudes. Here it is shown that a Rossby wave with a source in the tropical Pacific can explain the general pattern of teleconnection found during the southern winter. Upper level divergence associated with deep convection in the tropical Pacific plays a major role in the generation of these Rossby waves. SST anomalies associated with El Niño/Southern Oscillation force the tropical deep convection. However, the relationship between deep convection and SST anomalies is complex and modeling experiments show that in areas of large-scale subsidence positive SST anomalies would have to be larger than any observed anomalies (>4°C) before they have any effect on the vertical motion. Large variations are observed between the high-latitude response to El Niño with apparently similar tropical forcings. This makes accurate prediction of the high-latitude response to tropical change difficult. Ensemble GCM runs show that variations due to the natural variation of the zonal flow in the Southern Hemisphere can swamp the signal resulting from changes in the Rossby wave source region.

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