The North Pacific Climate Regime Shift In 1989 And North Pacific Gyre Oscillation

Some studies have found a climate regime shift occurred in the North Pacific around 1989,which is associated with the enhancement of North Pacific Gyre Oscillation(NPGO).In present study,on the basis of satellite observations and atmospheric and oceanic reanalysis datasets,the major characteristics of North Pacific atmospheric and oceanic variables at different period have been compared.We analyzed the characteristic of the climate regime shiftin 1989 and the role that NPGO played in it,then discussed its relationship with Tropical Pacific and Kuroshio Extension(KE)ocean-atmosphere interaction.Our results suggest that during 1989-2004,the first two EOF modes of Northeast Pacific SSHA reversed and the first EOF mode became NPGO.During this period,the SSH of subtropical gyre and subpolar gyre in the Northeast Pacific changed from same phase to slight anti-phase.And the EOF1 of North Pacific SSTA was more similar to NPGO-like SSTA.At the same time,the first EOF mode of North Pacific SLP and wind anomalies was still more similar to PDO-like SLP and wind anomalies.There was no significant change compared to 1950-2015 on North Pacific ocean-atmosphere interaction,but during 1989-2004,the results of EOF and SVD were more similar,showing that the North Pacific ocean-atmosphere interaction was stronger in 1989-2004.High-frequency component of NPGO(NPGOH)is closely related to Tropical Pacific.NPGOH can drive ENSO events in the next year by Seasonal Footprinting Mechanism,then ENSO will reacts back to North Pacific via atmospheric teleconnection mechanism,so NPGOH and NIN03.4 index have similar interannual variation.Low-frequency component signals of NPGO(NPGOL)propagate westward in the form of baroclinicRossby wave into the KE region,which leads to the decadal variability of KE.The variability of KE will change the ocean-atmosphere interaction in KE region and influence the SLPA field in Northeast Pacific,which produces a negative feedback for NPGOL.The most obvious feature of the climate regime shift in 1989 is the significant enhancement of NPGOL,which indicates that the North Pacific ocean-atmosphere interaction related to NPGOL may play a key role in this climate regime shift.