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Observations of Energy Dissipation in the Wake of a Western Pacific Typhoon

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LONG-TERM GOALS. We are focused on understanding small-scale processes that influence the ocean s thermodynamic and dynamic properties on the sub-mesoscale scales less than 10 km. This includes the turbulent evolution of cold wakes caused by typhoons, and the subsequent mixing processes the restore the upper ocean stratification after a storm event. OBJECTIVES. We investigated the energy dissipation properties of the mixed layer and mixed-layer base thermocline transition layer in the aftermath of typhoon Fanapi in the period 21 September 11 October 2010. During the initial week of the survey on the RV Revelle, a well-defined cold wake was identified and sampled in the area east of the Ryukyu Islands. The wake was 3 days old when it was initially sampled, and was crossed on 3 occasions over 4 successive days in the 21-25 September 2010. Turbulence levels were measured with a VMP-500 free-falling turbulence profiler, equipped with dual shear and temperature microstructure probes as well as a Seabird CTD. The system was used to profile to depths of 200 to 400 m, well into the mixedlayer thermocline transition layer. Analysis of temperature and dissipation data from the wake crossings are reported here. We find elevated levels of turbulence linger in the wake up to 1 week after its generation. The enhancement is specifically in the deep part of the wake, roughly at 100-m depth for the case of Fanapi. At shallower depths, the turbulence levels appear reduced relative to the areas on either side of the wake, apparently due to the suppression of turbulence caused by the increased nearsurface stratification. Within the wake, it appears the turbulence levels are enhanced to the right of the wake s center, consistent with the symmetry in forcing.

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  • Meteorology

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