scholarly journals Intrinsic low-frequency variability and predictability of the Kuroshio Current and of its extension

2014 ◽  
Vol 5 (2) ◽  
pp. 79 ◽  
Author(s):  
Stefano Pierini ◽  
Henk A. Dijkstra ◽  
Mu Mu
Keyword(s):  
Particle Filtering ◽  
Current System ◽  
Kuroshio Extension ◽  
Low Frequency ◽  
Kuroshio Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Model Studies ◽  
Low Frequency Variability ◽  
The Kuroshio

Investigations of the intrinsic low-frequency variability and predictability of the Kuroshio Current and of its extension jet (the Kuroshio Extension, KE) are reviewed. The Kuroshio and KE in the North Pacific constitute a western boundary current system of great relevance from climatological and ecological viewpoints. Both the Kuroshio south of Japan and the KE display remarkable changes of bimodal character on interannual time scales that are believed to be intrinsic, i.e., basically generated by nonlinear oceanic mechanisms rather than by direct atmospheric forcing. Model studies of the Kuroshio and KE with climatological forcing are thus reviewed. Moreover, as these changes are chaotic, their predictability requires peculiar mathematical approaches: theoretical results concerning this important issue are therefore reviewed as well. Model studies aimed at determining the optimal precursors and optimally growing initial errors for the Kuroshio are described. Techniques based on Lyapunov exponents (including their Lagrangian extension) and on data assimilation techniques (namely, sequential importance sampling using a particle-filtering approach) are reviewed for the KE. The key problem of how to identify the areas where targeted observations can improve the forecast is also addressed. The role of wind forcing in triggering the KE oscillations is finally considered.

scholarly journals On the Crucial Role of Basin Geometry in Double-Gyre Models of the Kuroshio Extension

2008 ◽  
Vol 38 (6) ◽  
pp. 1327-1333 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Crucial Role ◽  
North Pacific Ocean ◽  
Kuroshio Extension ◽  
Low Frequency ◽  
Altimeter Data ◽  
Western Boundary ◽  
Low Frequency Variability ◽  
Basin Geometry ◽  
The Kuroshio ◽  
Double Gyre

Abstract The decadal chaotic relaxation oscillation obtained in a recent double-gyre model study of the Kuroshio Extension intrinsic low-frequency variability was found to compare surprisingly well with the real variability of the jet as revealed by altimeter data, despite the high degree of idealization of the model. In this note it is shown that elements of realism in the basin geometry, present in that study and absent in previous double-gyre models applied to the Kuroshio Extension, play a crucial role in shaping the low-frequency variability of the jet, and can explain the good performance of the model. A series of numerical experiments with different basin geometries of increasing degrees of simplicity are analyzed. If the schematic western boundary representing the coastline south of Japan is removed, the strong decadal variability completely disappears and only a very weak periodic oscillation about an elongated state of the jet is found. If the large zonal width of the basin (representing correctly the extension of the North Pacific Ocean) is reduced by a half, then the total meridional Sverdrup transport is reduced by the same factor, and so is the intensity of the Kuroshio and Oyashio western boundary currents: as a result, the modeled Kuroshio Extension is totally unrealistic in shape and is steady. If both simplifications are introduced the resulting jet is, again, totally unrealistic, yielding a weak periodic bimodal cycle. On the basis of these results, two main conclusions are drawn: (i) the introduction of appropriate geometrical elements of realism in double-gyre model studies of the Kuroshio Extension is essential, and (ii) the Kuroshio Extension intrinsic low-frequency variability would be dramatically different if the southwestern coastline of Japan were more meridionally oriented.

Ship Routing Based on the Kuroshio Current

2017 ◽  
Author(s):  
Chen Chen ◽  
Masashi Kashiwagi
Keyword(s):  
North Pacific Ocean ◽  
Kuroshio Current ◽  
Ocean Model ◽  
Ocean Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Ship Maneuvering ◽  
Ship Routing ◽  
Ship Navigation ◽  
The Kuroshio

As a strong western-boundary current, the Kuroshio Current has significant effects on the ship navigation in the East China Sea (ECS). To quantitatively know more about its influence, we present simulations of the ocean current in the North Pacific Ocean using the well-known Princeton Ocean Model (POM). The high-resolution current distributions could be applied to conduct numerical simulations of the ship navigation, which utilized a ship maneuvering model known as the Mathematical Maneuvering Group (MMG). Calculation of a container ship as well as a training ship have been conducted. The simulation results of both ships can show the significant effects of ocean currents on ship’s drifting as well as speed change, which could be used to optimize cost of both fuel and time by properly utilizing the current in ship routing.

scholarly journals Coherence Resonance in a Double-Gyre Model of the Kuroshio Extension

2010 ◽  
Vol 40 (1) ◽  
pp. 238-248 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Time Scale ◽  
Kuroshio Extension ◽  
Relaxation Oscillation ◽  
Low Frequency ◽  
Altimeter Data ◽  
Coherence Resonance ◽  
Wind Noise ◽  
Low Frequency Variability ◽  
The Kuroshio ◽  
Double Gyre

Abstract The effect of stochastic winds on the intrinsic low-frequency variability of the Kuroshio Extension (KE) is analyzed through a double-gyre (DG) model forced by a steady climatological wind plus an idealized Ornstein–Uhlenbeck wind noise. A DG model of the KE bimodality, whose results compare well to altimeter data, is first shown to be an excitable system. In fact, the relaxation oscillation (forced by steady winds) with decadal time scale that describes the bimodality is recognized to be an internal mode of the system, which can be excited also in a dissipative parameter range (PR) in which it does not arise spontaneously, provided appropriate initial conditions are chosen. It is then shown that, if the additive wind noise is included in the forcing, the actual excitation of the relaxation oscillation in PR occurs if the noise is red with a decorrelation time greater than a minimum time scale ranging from 1 month to 1 year, depending on the dissipation. This behavior, known as “coherence resonance,” is likely to be paradigmatic of the low-frequency variability of western boundary current extensions of intrinsic origin, when it is in the form of relaxation oscillations resulting from a homoclinic bifurcation. General considerations concerning the interpretation of model results obtained within different parameter ranges are applied to this study.

scholarly journals Mechanisms of Decadal Variability of the Wind-Driven Ocean Circulation

2005 ◽  
Vol 35 (4) ◽  
pp. 512-531 ◽  
Author(s):  
Andrew Mc C. Hogg ◽  
Peter D. Killworth ◽  
Jeffrey R. Blundell ◽  
William K. Dewar
Keyword(s):  
Flow Field ◽  
Ocean Circulation ◽  
Potential Vorticity ◽  
Decadal Variability ◽  
Low Frequency ◽  
Ocean Basin ◽  
Western Boundary ◽  
Boundary Current ◽  
Low Frequency Oscillations ◽  
Low Frequency Variability

Abstract Eddy-resolving quasigeostrophic simulations of wind-driven circulation in a large ocean basin are presented. The results show that strong modes of low-frequency variability arise in many parameter regimes and that the strength of these modes depends upon the presence of inertial recirculations in the flow field. The inertial recirculations arise through advection of anomalous potential vorticity by the western boundary current and are barotropized by the effect of baroclinic eddies in the flow. The mechanism of low-frequency oscillations is explored with reference to previous studies, and it is found that the observed mode can be linked to the gyre mode but is strongly modified by the effect of eddies.

scholarly journals Low-frequency variability of the Kuroshio Extension

2009 ◽  
Vol 16 (6) ◽  
pp. 665-675 ◽  
Author(s):  
S. Pierini ◽  
H. A. Dijkstra
Keyword(s):  
Nonlinear Dynamics ◽  
Large Scale ◽  
Rossby Waves ◽  
Kuroshio Extension ◽  
Baroclinic Instability ◽  
Low Frequency ◽  
Wave Dynamics ◽  
Low Frequency Variability ◽  
Low Dimensional ◽  
The Kuroshio

Abstract. In this paper, we provide a review of recent results targeted at the understanding of the low-frequency variability of the Kuroshio Extension. We provide the background and main arguments of two views which have recently been proposed to explain this variability. In the first view, wind-induced Rossby waves and the effects of mesocale eddies are crucial. The second view is based on low-dimensional equivalent-barotropic large-scale nonlinear dynamics, with neither Rossby wave dynamics nor baroclinic instability being important. Results from models supporting each view are discussed and confronted with results from available observations.

Sign in / Sign up

Export Citation Format

Share Document