The OFES simulations were conducted on the Earth Simulator under the support of JAMSTEC. We thank Drs. Y. Masumoto, H. Sakuma, T. Yamagata, and the OFES group members for their efforts and supports in the model development. Comments from Drs. S. Ito, H. Saito, A. J. Miller, and anonymous reviewers were very helpful. This study is supported in part through the research project Population Outbreak of Marine Life (POMAL) by the Agriculture, Forestry, and Fisheries Research Council of Japan and through Grant-in-Aid for Scientific Research in Innovative Areas 2205 (Grant 22106006) by the Japanese Ministry of Education, Culture, Sports, Science and Technology, and also through Grant 21540458 by the Japan Society for the Promotion of Science.
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The meridional span of the linear model used for their prediction is 35°–40°N, although its results are compared with SST at 40°N in their Fig. 1.
As shown in Fig. 5, the simulated KE jet axis tends to be situated slightly to the north of its counterpart in observations. As a result, the interannual variability in Fig. 1 is weaker in OFES, especially in 1990–95, as the area-mean heat content is less influenced by strong variability of the KE jet. This bias in the KE latitude, however, does not affect our analysis of predictability of the KE jet speed, which is defined at the jet axis rather than at prescribed latitude.
The corresponding skills based on the first- and second-order autoregression simulations are found to be lower than that for the persistent anomalies. Although the KE jet speed time series shows low-frequency variability, its phase changes because of the nonlocal Rossby wave propagation and not because of some stochastic process. Then, the autoregressive models cannot represent the phase changes.