title: How potentially predictable are midlatitude ocean currents?
abstract: Predictability of atmospheric variability is known to be limited owing to significant uncertainty that arises from intrinsic variability generated independently of external forcing and/or boundary conditions. Observed atmospheric variability is therefore regarded as just a single realization among different dynamical states that could occur. In contrast, subject to wind, thermal and fresh-water forcing at the surface, the ocean circulation has been considered to be rather deterministic under the prescribed atmospheric forcing, and it still remains unknown how uncertain the upper-ocean circulation variability is. This study evaluates how much uncertainty the oceanic interannual variability can potentially have, through multiple simulations with an eddy-resolving ocean general circulation model driven by the observed interannually-varying atmospheric forcing under slightly different conditions. These ensemble "hindcast" experiments have revealed substantial uncertainty due to intrinsic variability in the extratropical ocean circulation that limits potential predictability of its interannual variability, especially along the strong western boundary currents (WBCs) in mid-latitudes, including the Kuroshio and its eastward extention. The intrinsic variability also greatly limits potential predictability of meso-scale oceanic eddy activity. These findings suggest that multi-member ensemble simulations are essential for understanding and predicting variability in the WBCs, which are important for weather and climate variability and marine ecosystems.
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan.
authors.forename: Masami
authors.initials: M
authors.lastname: Nonaka
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Sasai
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan.
authors.forename: Hideharu
authors.initials: H
authors.lastname: Sasaki
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan.
authors.forename: Bunmei
authors.initials: B
authors.lastname: Taguchi
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan.|Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, 153-8904, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Nakamura
references.citation: Proc Natl Acad Sci U S A. 1947 Nov;33(11):318-26
references.pmid: 16588757
references.citation: Science. 1977 Sep 16;197(4309):1179-81
references.pmid: 17753335