OC4331-Mesoscale Oceanography
Final Project Summary

Topic Area: Instability of the Subtropical Front

LT Keir Stahlhut, USN

Ultimate question: How does the SFZ influence the eddy field in the (Western) Sargasso Sea???

SFZ structure: The SFZ is evident as a zonal band between about 26N and 32N where subtropical frontogenesis between westerlies and trades enhance the slope of the mean seasonal thermocline.

Demonstrate: 1) Mean flow in SFZ is baroclinically unstable 2) Characterization of time-dependent properties of the turbulent eddy field that evolve due to this instability

Analysis Methods:

• Using a three active layer model, analytically characterize properties of the unstable eddies during early growth stages
• Estimate “most unstable” growth rate and wavelengths
• Consider absolute stability properties
• Numerical model analysis of three active layer model for later growth stages, to study the non-linear effects
• Compare these results to satellite and XBT data of eddies

Conclusions: Model results suggest baroclinic energy conversion and atmospheric forcing contribute roughly equally to eddy variability within the SFZ, which agrees with linear theory dealing with the seasonal thermocline, linear eigenvalue problem analysis, recent non-linear stability theories, and analysis of historical XBT data.

Powerpoint Presentation on this paper....

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Figure 1. Map showing Sargasso Sea (from National Geographic).

Figure 2. Vertical Meridional Cross Section.

Figure 3. Recent Depth of 26C isotherm chart for Western Sargasso.

Figure 4. Recent SST chart for Western Sargasso.

Halliwell, G.R., G. Peng, and D.B. Olson, 1994: "Stability of the Sargasso Sea Subtropical Frontal Zone." J. Phys. Oceang., Vol. 24, 1166-1183.

"Atlantic Tropical Weather" wesite. Links to various charts and products, including NOAA produced .gifs. http://www.atwc.org/

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