ENSO Teleconnection to the Isopycnal Depth Fluctuations of the East/Japan Sea Intermediate Water in the Ulleung Basin during 1968–2002

This study first detects the decadal variability in the depths of the East/Japan Sea (EJS) Intermediate Water (ESIW) using in situ observations and relates it to strong El Niño–Southern Oscillations (ENSOs). Using multitaper cross-spectrum and cyclostationary empirical orthogonal function analysis, this study found significant coherences at the 99% confidence level and opposite phases between Niño-3 and the ESIW isopycnal depths in the Ulleung Basin (UB) at a period of 14.1 yr during 1968–2002. This suggests a teleconnection between strong ENSOs and the ESIW, the cause of which is explored. When a strong El Niño (EN) develops, the Pacific–North American pattern is intensified by the EN-related Rossby wave interfering constructively with the climatological stationary wave. The amplified wave propagates upward into the stratosphere and breaks, weakening the polar vortex. The EN-related geopotential height increases over the pole with poleward converging air and decreases over the Yakutsk Basin (YB), indicating a negative northern annular mode with the south-to-north gradient balancing the easterly anomaly that responds to vortex weakening. The converged air at the pole warms adiabatically and raises the height as it sinks. This height distribution, including the east-to-west gradient balancing the southward flow, induces the polar vortex split into two with the colder one in the YB where the EJS is closer than from the pole. The EN-related northwesterly wind directing toward the EJS is also strong. Thus, the coldest air with negative wind stress curls reaches the EJS quickly and forms more ESIW, which converges into the UB, causing the observed decadal isopycnal fluctuations.