Inter El NiÑo variations in the atmospheric circulation of the South Pacific, part II—modelling

The response of the Hadley Centre atmosphere only model (HadAM3) in the southeast Pacific and Antarctic Peninsula to El Nino forcing is investigated. The El Ninos area forced by imposing observed sea surface temperatures. Two different families of runs are used. One uses observed global temperatures and so includes extra tropical ocean variations. The other imposes sea surface temperature anomalies associated with individual El Nino events onto a yearly repeating SST climatology. The first set of runs enable us to investigate how well the Hadley Centre model reproduces the observed extra tropical response to individual El Nino events. The second set of runs allows the atmosphere only link between the tropical Pacific and the southeast Pacific and Antarctic Peninsula to be studied. Observational and modelling studies have shown that the link between the tropics and the southeast Pacific take the form of a Rosby Wave Train.

This approach allows the effect of different individual El Nino events on the extra tropical circulation in the South Pacific to be studied. The role of convection in the tropical Pacific, within the models, in forcing the observed Rossby Wave train is investigated.