Final Project Summary
Topic Area
The Intergyre Chaotic Transport
Project Team Member(s)
LT Max Salazar, USN
Major Findings
The concept of intergyre chaotic transport was derived from the idea of chaotic advection that was discovered in the mid-1980s. Though, the word chaos may seem daunting, it nonetheless provided no significant difficulties beyond that of typical oceanographic dynamics. The model was basically set up by adopting a homogeneous ocean with a flat bottom, Sverdrup flow in the interior, and a Stommel boundary layer along the western boundary.
The basic idea of intergyre chaotic transport is that an exchange of water mass and its properties will be advected from one gyre to another in the presence of a temporally varying gyre circulation that results from an annually migrating meridional wind field. Further, this transport is affected by forcing in the frequencies between annual to interdecadal. As a result of this frequency dependence, an optimal frequency and amplitude exist for the chaotic transport. Further, in spite of weak eddy mixing, chaotic transport was proven to have a more significant impact on tracer evolution than time mean forcing and pure diffusivity. In strong eddy mixing, chaotic transport was comparable to that of time mean forcing but still dominated over pure diffusivity.
The most important aspects of chaotic transport include:
- The chaotic intergyre transport produces strong mixing between gyres.
- The chaotic transport is strongest under a migration field with interannual to decadal frequencies and with a migration distance of about 1000 km.
- Intergyre transport and mixing as a result of a migrating wind is comparable to the effects of strong eddies.
- The intergyre boundary is a orbit connected upon two saddle points on the eastern and western boundaries that becomes chaotic when perturbed.
Figure 1. The case of annual wind migration with ω =50 and a = 0.2;
cross-gyre transport obvious.
Figure 2. Particle dispersion diagram of the distribution of 10000 particles at
t = 1.8.
References
Zhengyu, L., H. Yang, 1993: "The Intergyre Chaotic Transport." J. Physical Oceanography. Vol. 24, 1768-1782.