Research and development of the radar system for monitoring the variability of surface current in coastal and strait areas

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1. Developing the current monitoring system based on HF radar and the methods for analyzing the data obtained by that system.Radar measurement often suffers from its limited accuracy and insufficient number of data. Moreover HF radar fails to measure the current sometimes in some part of the observation area. We therefore developed general methods for interpolating and estimating the current field with application to HF radar measurement in mind. 1) The standard analysis used when 2 units of radar are available is generalized to the case of an arbitrary number of radar units in a single area. 2) The harmonic interpolation method was developed, which proved quite simple, robust and useful. 3) The harmonic interpolation method was generalized to the least square method with harmonic interpolation. 4) Hydro-dynamical meaning was given to the harmonic interpolation method. 5) Useful representation was derived for general orthogonal curvilinear coordinates, including the polar coordinate sy … More stem used in HF radar measurement.2. Oceanography on the variability of the surface current in the Tsushima Strait revealed by HF radar.2.1) Our radar system often detected the Tsushima Eddy, east of Tsushima. It is a sub-mesoscale anti-clockwise eddy of the same size as Tsushima. We analyzed the spatial and temporal properties of Tsushima Eddies on the basis of the accumulated data obtained by HF radar. Strong and notable Tsushima Eddies tend to be generated in summer to autumn. They are likely to be born at intervals of 4-6 days or 10-12 days. They seem to be shed at the southeastern tip of Tsushima, drifting northeastward. These results suggested that the generation of Tsushima Eddies is controlled by the intensity of the Tsushima Warm Current, the fortnightly cycle of the spring-neap tide and seasonal variation of the density stratification; the Tsushima Eddies are found in the wake of Tsushima against the northward flowing Tsushima Current with relatively strong alternating tidal current superimposed.2.2) We analyzed the seasonal variation of the surface current in the Tsushima Strait on the basis of the accumulated current maps of the monthly mean current field obtained by the HF radar system. In summer, southwestward flowing counter current appears east of Tsushima. In winter surface current in the eastern channel of Tsushima Strait seems to flow southeastward to Fukuoka, a curious result Substantial current becomes visible, however, if the wind-drift current estimated adequately is eliminated from monthly mean current; .seemingly southeastward surface current in winter is mostly ascribed to the wind-drift component due to monsoon. On the other hand from summer to autumn, frequent generation of Tsushima Eddies, east of Tsushima, was confirmed as was described in 2.1) It is suggested therefore that the southwestward mean counter current east of Tsushima in summer represents the average of definitely anti-clockwise eddies (Tsushima Eddies) activated in the eastern wake of Tsushima in summer. Less