Nonlinear response of western boundary currents to variable wind forcing

Program Code: 
1082
Contact: 

Dr Andrew Kiss (a.kiss@adfa.edu.au)

Description of Work: 

Objectives:

This project will investigate the nonlinear response of western boundary currents (WBCs, such as the Kuroshio) to variations in wind forcing. Western boundary currents have intrinsic variability due to their instabilities, but they are also driven (indirectly) by winds which have their own time-dependence, such as an annual cycle. Observed WBC variability may therefore be due to the interaction between intrinsic instabilities and variations in wind forcing. Western boundary currents are nonlinear, and initial investigations (Kiss, 2007) have shown that their response to variable forcing includes nonlinear resonance and chaos, as expected for a driven nonlinear oscillator.

The chaotic response is particularly interesting, because it leads to variability on timescales far longer than either the forcing variability or the intrinsic WBC variability, which may possibly pay a role in climate variability.

Description of Work:

The project will investigate this problem using MITgcm, Q-GCM or a similar model, using a dynamical systems (“chaos theory”) approach to analyse the dynamics. Initial experiments will use an idealized “box ocean” to cleanly reveal the physics. Further work could investigate the effects of more realistic bathymetry and boundary shape, and also the effects of two-way ocean-atmosphere coupling.

Reference:

A. E. Kiss (2007) “Nonlinear resonance and chaos in an ocean model”, Proc. CSIRO Centre for Complex System Science & COSNet.

Workshop on Turbulence and Coherent Structures in Fluids, Plasmas, and Granular Flows, The Australian National University, 10 - 13 January 2006, World Scientific Lecture Notes in Complex Systems.