Short-range prediction experiments of the Kuroshio path variabilities south of Japan |
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| Authors: | Norihisa Usui Hiroyuki Tsujino Yosuke Fujii Masafumi Kamachi |
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| Institution: | (1) Oceanographic Research Department, Meteorological Research Institute, Nagamine 1-1, Tsukuba 305-0052, Japan |
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| Abstract: | Assimilation and prediction experiments of the Kuroshio path variability south of Japan were conducted to investigate the
predictability of the Kuroshio path. The assimilation and prediction system is composed of an eddy-resolving model and a three-dimensional
variational analysis scheme with vertical coupled temperature–salinity empirical orthogonal function modes. The sea surface
height (SSH) variability and the variations of the Kuroshio path of the assimilation fields are in good agreement with those
observed. The results of the assimilation are then used as the initial conditions for 138 cases of 90-day prediction experiments
conducted from 1993 to 2004. The predictive limit of our system is assessed by the SSH anomaly in the assimilation field and
is found to be around 40–60 days, which is much longer than that of the persistence. The prediction results show good performance
in the transition stage from a straight to a meandering path. For example, a large meandering event that occurred in August
2004 is successfully predicted in a 2-month forecast. Two types of failure cases are investigated. One is a case where the
eastward propagation speed of the meander is faster than a real state. The dynamical response of the model to the assimilation
revealed that an initial shock, caused by the dynamically unbalanced initial condition, induces the fast eastward propagation
of the meander. The other case exhibits an unrealistic meander. In this case, a cold anomaly at an intermediate layer in the
initial condition grows rapidly and results in the unrealistic meander. This implies that the Kuroshio path south of Japan
has a chaotic nature. These facts revealed by the failure cases give us some insight for improving the predictive skill of
the Kuroshio path variability. |
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| Keywords: | Kuroshio path Kuroshio large meander Data assimilation Short-range prediction Predictive limit Baroclinic instability |
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