Two types of El Nino and extratropical sea-level pressure variations

This study applies the nonlinear canonical correlation analysis (NLCCA) to explore the nonlinear relationship between the sea-level pressure (SLP) anomalies over the extratropical North Pacific and sea surface temperature (SST) anomalies in the tropical Pacific during 1985-2009. Our results suggest that the asymmetry between the warm eastern Pacific (EP) El Nino-Aleutian Low mode and the cool EP La Nina-antiphase of the Aleutian Low mode is exhibited in the first NLCCA mode. Nonlinearity of the first NLCCA SST field is enhanced after 1998, and vice versa for the SLP field. The second NLCCA SSTmode reveals weak nonlinearity representing the nonlinear central tropical Pacific (CP) El Nino-CP La Nina modes, while the second SLP field depicts the North Pacific Oscillation and anti-phase with the Aleutian Low phases. The nonlinearity of the second SST and SLP NLCCA modes is found to decrease gradually with time. During 1985-1997, the SST field exhibits linearity, while the SLP field shows weak nonlinearity. During 1997-2009, the SST and SLP fields both display weak linearity. Nonlinearity between the extratropical SLP and SST fields is further weakened from the first period. The Aleutian Low pattern could be excited by both EP and CP El Ninos. Moreover, the CP El Ninos have more connections with the North Pacific Oscillation state rather than the EP El Ninos. Conclusively, this study reveals the asymmetric-modes between the SLP and SST by the nonlinear method, and contributes to the understanding of the extratropical SLP variability response to two types El Nino events.