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2. Turbulence inside the Shikoku-Basin and Kuroshio meandering 
2.1 Wavelet analysis of K-U index 
A disadvantage of NOAA-AVHRR-based turbulence survey is so frequent interruption by 
cloud cover. To break through, a time series signal K-U index was introduced; i.e. difference in the 
sea surface elevations picked up at two tide gauge stations named Kushimoto and Uragami , located 
at the top of the most distinguished Giant-Cusp, the Cape-Shionomisaki as shown in Figure 3(a). 
Lower frequency components of K-U index has been used to identify the meandering path 
of Kuroshio; i.e. the up and downs with month-years in time scale respond to nonmeander and 
meander (Kawabe 1980). For the hydrodynamics of turbulence, we have exploited its higher 
frequency region; i.e. up and downs of K-U index was physically reasoned to be caused by those in 
the dynamic pressure of the Kuroshio impinging upon the top of the cape (Nishimura et al. 1986). 
Figure 3(b) shows the K-U index diagram in the first half 1993. The gray-scale image 
shows the wavelet modulus of original signal, and the time series curve is the lowpass filtered K-U 
index , which was gained through inverse wavelet transform of the components with time scales 
larger than 36 hours. Synthesizing the diagram with NOAA/AVHRR-based measurements, we can 
analyze the turbulence hydrodynamics decomposing into space, time and frequency domains. 
2.2 Eddy shedding from Giant-Cusps and coastwise turbulent boundary layer 
Figure 4 displays the NOAA data of turbulence, 4 February 1993. At this time stage of 75 
days earlier than in Figure 1, the Kuroshio was taking a nonmeandering path near the Pacific-Coast. 
Inside the coastwise turbulent boundary layer, cyclonic eddies of less than 100km in size were being 
shed into the main stream from the tops of Giant-Cusps. 
The most efficient vortex generator is the Cape-Shionomisaki, from which a cyclone is 
being shed. Running along its circumference, Kuroshio watermass is entrained into coastal zone 
directly from offshore, which the coastal fishermen named "kyuu-Chou". Owing to the coherence 
in the eddy structure, outer edge of boundary layer is so sharp, which is generally called "Shiome". 
Time scale of this eddy shedding process was estimated at a few days. In the K-U index diagram, 
Figure 3. Coherent structure analysis of the Kuroshio in the space, time and frequency domains, 
(a) NOAA/AVHRR image overlaid with instantaneous turbulence field, (b) K-U index diagram.