[A-CG31] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG31-04] Interdecadal modulation of the relationship between the decadal variability of the Kuroshio Extension and the central tropical Pacific in an eddy-resolving coupled model

*Yukito Tamura^1,2, Tomoki Tozuka^1,2 (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 2.Application Laboratory, Japan Agency for Marine-Earth Science and Technology)

Keywords:Kuroshio Extension, decadal variability, high-resolution CGCM, teleconnection, Kuroshio large meander

The Kuroshio Extension (KE) is known to undergo large decadal variations, especially after the 1976/77 Pacific climate regime shift. Due to strong ocean-atmosphere interactions over the KE, the region may be a key region for basin-scale Pacific climate variability. Recently, it has been suggested that an atmospheric teleconnection from the central tropical Pacific dominantly forces the KE decadal variability via westward propagating oceanic Rossby waves. However, the relationship between the KE and the central tropical Pacific varies on interdecadal timescale, and this relationship becomes statistically significant only after the regime shift. Since it is difficult to reveal mechanisms of the interdecadal modulation due to the lack of sufficiently long observations, outputs of an unprecedented 500-year pre-industrial control simulation by an eddy-resolving coupled general circulation model (CGCM) are used to investigate the possibility and mechanisms of natural variability-induced interdecadal modulation. The eddy-resolving ocean model component can realistically reproduce the KE and associated anomalies. The entire integration period is first divided into five segments, and subsequent analyses show diverse characteristics among each period. A qualitatively similar relationship between the KE and the central tropical Pacific to that in the post-regime shift period is found in the period with the strongest and most persistent variability in the central tropical Pacific. In contrast, such a relationship cannot be seen in the other periods, probably being disrupted by shorter persistence of the tropical variability, the location of the atmospheric teleconnection, and/or influences of the Kuroshio large meander. These findings suggest that the interdecadal modulation may occur even without anthropogenic forcing. Furthermore, amplitude and persistence of the central tropical Pacific variability are suggested to be crucial for its tight relationship with the KE through the atmospheric teleconnection and oceanic Rossby waves.