11:30 AM - 11:45 AM
[ACG36-04] Interdecadal modulation of the North Pacific Oscillation and its interaction with the central tropical Pacific and the Kuroshio Extension in an eddy-resolving CESM
Keywords:Kuroshio Extension, North Pacific, North Pacific Oscillation, decadal variability, eddy-resolving coupled model, tropical Pacific
The Kuroshio Extension (KE) is considered to play a crucial role in basin-scale climate variability due to intense and coherent ocean-atmosphere interactions. The KE has exhibited significant decadal variations since the 1976/77 Pacific climate regime shift. Recent studies suggest that sea surface temperature (SST) anomalies in the central tropical Pacific dominantly force the KE via an North Pacific Oscillation (NPO)-like atmospheric teleconnection and oceanic Rossby wave adjustment. Although this relationship is statistically significant after the regime shift, it varies on interdecadal timescales. Our previous study, which analyzed a 500-year simulation using an eddy-resolving Community Earth System Model (CESM), revealed that the KE and central tropical Pacific covary when decadal variability in the central tropical Pacific is sufficiently strong, as observed in the post-regime shift period.
In this study, interactions between tropical decadal variability, basin-scale atmospheric variability over the North Pacific, and the KE are examined using the same simulation. While strong tropical variability energizes the low-frequency component of the NPO, the NPO, in turn, amplifies tropical SST anomalies by driving the Pacific Meridional Mode (PMM) through the wind-evaporation-SST (WES) feedback. Moreover, the southward migration of the background westerly jet over the eastern North Pacific may provide favorable conditions for a robust positive feedback between the NPO and the tropics. As the NPO expands southward, it can more efficiently drive the PMM. Consequently, the enhanced low-frequency NPO forces the KE via oceanic Rossby waves.
In this study, interactions between tropical decadal variability, basin-scale atmospheric variability over the North Pacific, and the KE are examined using the same simulation. While strong tropical variability energizes the low-frequency component of the NPO, the NPO, in turn, amplifies tropical SST anomalies by driving the Pacific Meridional Mode (PMM) through the wind-evaporation-SST (WES) feedback. Moreover, the southward migration of the background westerly jet over the eastern North Pacific may provide favorable conditions for a robust positive feedback between the NPO and the tropics. As the NPO expands southward, it can more efficiently drive the PMM. Consequently, the enhanced low-frequency NPO forces the KE via oceanic Rossby waves.