Turbulent kinetic energy dissipation rate observations in the cold wake of Typhoon Fanapi

Typhoon Fanapi formed in the western North Pacific Ocean, and became a named storm on September 14, 2010 in the vicinity of 129.1 E, 19.6 N. It subsequently traveled westward across the Philippine Sea and came ashore near Hualien, Tawain as a category 3 storm on the Saffir-Simpson scale (winds of 120 miles per hour) on September 19, 2010. The storm created a strong cold wake in the ocean along its path. Following the landfall of the typhoon, a research cruise abroad the R/V Revelle was undertaken to study the structure, evolution, and decay of the cold wake as part of the Impact of Typhoons on the Pacific (ITOP) study. Here we present observations of the cold wake revealing the residual turbulent kinetic energy after the storm. Hydrographic and velocity observations were made with coincident turbulence observations, made with a tethered free-falling profiler measuring shear microstructure. This data record allows us document the turbulent kinetic energy dissipation rate over a period spanning 3 to 18 days after the passage of the storm. In the near-surface layer (z<50-m depth), turbulent kinetic energy (TKE) dissipation rates were suppressed in the cold wake, relative to levels outside the wake, as a result of the increased stratification. It would appear that any enhancement of turbulence occurring in the near-surface layer had dissipated by the 3rd day after the storm's passage. However, below the cold wake, TKE dissipation rate levels decayed in the 2-week period after the storm, consistent with the decay on near-inertial energy. The results suggest that cold wakes may be an effective way to boost mixing through the mixed-layer/thermocline transition zone that links surface forcing to ocean interior processes.