AVHRR images from the U.S. satellite NOAA-7 on May 18, 1982 showed the flow structure in the Japan Sea including the Tsushima Warm Current. There are many eddies which have the characteristics of horizontal turbulence with a structure like the bands of a spiral nebula. The high resolution wave-number spectrum of the sea surface temperature shows a well-defined peak at about 100 km corresponding to the size of the eddies, and a secondary peak at about 15 km corresponding to their banded structure. The spectrum has a slope proportional to k-3 in a range of wave numbers somewhat lower than the first peak, and the one of k-5/3 in wave numbers higher than the secondary peak. The latter range is now called a "pseudo three-dimensional range". A combination of the scale of the eddies with their known velocities gives the horizontal eddy diffusivity of 1.5 × 104 m2s-1 for the southern part and 5 × 103 m2s-1 for the northern part of the Japan Sea. The magnitude of the heat convergence in the Japan Sea, estimated by Kato and Asai (1983) in relation to the study of the air-sea heat exchange, can be explained by these values of the eddy diffusivity combined with the average temperature distribution. Temperature sections suggest a possible effect of the bottom topography through the eddies on the flow structure.
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