The East/Japan Sea (EJS), a marginal sea of the Northwestern Pacific, is one of the ocean regions showing the most rapid warming and greatest increases in ocean heatwaves over the last several decades. Predictability and skillful prediction of the summer season EJS variability are crucial, given the increasing severity of ocean temperature events impacting fisheries and reinforcing climate conditions like the East Asian rainy season, which in turn affects adjacent high-population density areas over East Asia. We use observations and the Geophysical Fluid Dynamics Laboratory (GFDL) Seamless System for Prediction and Earth System Research (SPEAR) seasonal forecast system to investigate the summertime EJS Sea Surface Temperature (SST) predictability and prediction skill. The observations and seasonal prediction system show that the summer season EJS SST can be closely linked to the previous winter air-sea coupling and predictable 8–9 months in advance. The SPEAR seasonal prediction system demonstrates skillful forecast of EJS SST events from summer to late fall, with added skill for long-lead forecasts initialized in winter. We find that winter large-scale atmospheric circulations linked to Barents Sea variability can induce persistent surface wind anomalies and corresponding northward Ekman heat transport over the East China Sea. The ocean advection anomalies that enter the EJS in prior seasons appear to play a role in developing anomalous SST during summer, along with instantaneous atmospheric forcing, as the source of long-lead predictability. Our findings provide potential applications of large-scale ocean-atmosphere interactions in understanding and predicting seasonal variability of East Asian marginal seas.

东/日本海（EJS）是西北太平洋的边缘海，是过去几十年来变暖最快和海洋热浪增加最多的海洋区域之一。鉴于海洋温度事件对渔业的影响日益严重，并加强东亚雨季等气候条件，进而影响东亚邻近的人口密度高的地区，因此对夏季 EJS 变化的可预测性和熟练预测至关重要。我们利用观测和地球物理流体动力学实验室 (GFDL) 无缝预测系统和地球系统研究 (SPEAR) 季节性预报系统来研究夏季 EJS 海面温度 (SST) 的可预测性和预测技能。观测和季节预报系统表明，夏季EJS海温与前期冬季海海耦合密切相关，可提前8~9个月进行预报。 SPEAR 季节性预报系统展示了从夏季到深秋的 EJS 海温事件的熟练预报，以及在冬季启动的长提前期预报的附加技能。我们发现，与巴伦支海变化相关的冬季大规模大气环流可以引起持续的表面风异常以及东海相应的北向埃克曼热输送。前几个季节进入 EJS 的海洋平流异常似乎在夏季异常海表温度的形成中发挥了作用，同时瞬时大气强迫也是长超前可预测性的来源。我们的研究结果为大规模海洋-大气相互作用在理解和预测东亚边缘海的季节变化方面提供了潜在的应用。