Separate the Role of Southern and Northern Extra-Tropical Pacific in Tropical Pacific Climate Variability

Observational and modeling studies have elucidated the influential role played by the southern and northern extratropical Pacific (SEP and NEP) forcing in shaping dynamics of tropical Pacific climate variability. However, the relative importance of the NEP and SEP and the timescale on which they impact the tropics remain unclear. Using a linear inverse model (LIM) that selectively incorporates or excludes tropical-extratropical coupling, we find a reduction in tropical interannual variability (similar to 40%) and low-frequency (sub-decadal to decadal) variability in the southeastern tropical Pacific region (similar to 70%) in the absence of SEP. Conversely, the absence of NEP yields no significant impact on tropical interannual variability but markedly diminishes low-frequency variability in the central tropical Pacific region (similar to 70%). LIM and statistic diagnostics on CMIP6 models show the low-frequency to total variability ratio in the tropical Pacific depending on their NEP and SEP representation. Models with more (less) low-frequency power tend to show stronger NEP (SEP) dynamics. The tropical Pacific climate variability exerts a strong impact on global climate, regional weather, and marine ecosystems. The tropical and extratropical Pacific are closely coupled with each other through oceanic and atmospheric processes. Previous studies have shown that the southern and northern extratropical Pacific (SEP and NEP) forcing greatly impact the tropical Pacific climate variability. To understand and predict tropical Pacific variability, it is necessary to study the relative importance and the timescale on which the SEP and NEP exert their influence. In this study, we use an empirical dynamical model to exclude the impacts of SEP or NEP on the tropical Pacific based on the observational data. We find that the absence of SEP leads to a significant reduction of interannual variance (similar to 40%) and the low-frequency (sub-decadal to decadal) variance in the southeastern tropical Pacific region (similar to 70%), while the absence of the NEP does not change the interannual variance but significantly reduces the low-frequency variance in the central tropical Pacific region (similar to 70%). In observations, the ratio of low-frequency to total tropical variability is 0.36, while CMIP6 models exhibit a wider range, with enhanced low (high) frequency power associated with stronger NEP (SEP) dynamics.