Forecasting Remote Atmospheric Responses to Decadal Kuroshio Transitions: Stable vs Unstable States

We isolate near-decadal ocean-atmosphere variability that links undulations on the seaward extension of the Kuroshio Current with downstream rainfall anomalies over the western North America and the U.S. Northwestern Pacific, based on observational estimates and global ocean eddy-resolving coupled retrospective initialized predictions. We show that the teleconnection between the current undulations and downstream rainfall can lead to improved sub-seasonal to seasonal predictions of precipitation over California, and we demonstrate that capturing these teleconnections requires coupled systems with sufficient ocean resolution (i.e., eddy-resolving). Concerning the near-decadal variability, we show a progression of a lower-tropospheric height dipole around the North Pacific and how these height anomalies lead to wind-driven oceanic Rossby waves that affect the mesoscale eddy activity in the Kuroshio extension with a time lag on the order of four years. Regarding the teleconnection between the current undulations and downstream rainfall, we analyze 35-years of retrospective initialized ensemble forecasts with an ocean eddy-resolving and an ocean eddy-parameterized coupled model. Not only does the ocean eddy-resolving model show sensitivity to Kuroshio extension variability in terms of California precipitation, but the ocean eddy-resolving forecasts also show improved forecast skill compared to the ocean eddy-parameterized model. The ocean eddy parameterized coupled model shows no sensitivity to Kuroshio extension variability.