Identifying Climate Modes Contributing to Sea Surface Salinity Decadal Variation in the North Pacific Ocean

Abstract

AbstractThe North Pacific sea surface salinity (SSS) decadal variation (NPSDV) plays key roles in tracing ocean circulation and hydrological cycle, and its contributing climate modes need to be identified. Three data sets, ORAS4, EN4.2.1, and GODAS, were first evaluated. An autoregressive lag 1 (AR‐1) process model, along with spectrum and correlation analysis, was then applied to the most robust SSS data set during 1980–2017. The AR‐1 reconstructed SSS anomalies explain up to 77% and 55% of the first two modes, respectively. As expected, the NPSDV arises from the superposition of SSS variations with different dynamical origins, including the reemergence, Eastern Pacific and Central Pacific El Niño–Southern Oscillation (ENSO) (EP‐ENSO and CP‐ENSO), Aleutian Low (AL), North Pacific Oscillation (NPO), and Kuroshio and Oyashio Extension (KOE) meridional and zonal modes (KOE‐M and KOE‐Z). Its first mode is 50% EP‐ENSO and 32% CP‐ENSO, while the second mode is 58% NPO and 54% CP‐ENSO. Specifically, stronger persistence in salinity explains most of NPSDV variance. The first mode resembles the EP‐ENSO pattern with a positive loading center in the eastern North Pacific, and the second mode resembles the CP‐ENSO (and also NPO) pattern with a positive loading center near the dateline, alike the contrasting EP‐ENSO and CP‐ENSO SSS flavors in the tropics. Besides, a fraction of the first mode notable in the KOE region is controlled by KOE‐Z and KOE‐M as intrinsic oceanic dynamics. The importance of AL to NPSDV, after removing the indirect impact of ENSO, is insignificant. A general NPSDV evolution was lastly revealed.