Surface currents in the Norwegian Channel measured by radar in March 1985

Surface currents, as measured by a land-based HF radar (CODAR), are presented. The experiment was carried out in the Norwegian Channel (59°N) from March 12 to 22, 1985. Two-dimensional surface currents were mapped every 2 h, or 1 h during periods of strong wind. The current shows a strong variability on small horizontal (several km) and short temporal (days) scales, containing a large amount of energy. The development of eddies could be studied, which rotated anticlockwise with velocities up to 80 cm s^-1 and remained stable for about one day. From time series at different positions, the semidiurnal tide and the wind-driven part of the current is estimated. The tidal currents confirm with already-known results. The ratio of current-to-wind velocity (0.019 and 0.010, for the north- and east-components, respectively) are derived from surface currents directly and may be more reliable than other estimates. The horizontal curl and divergence are calculated and presented for one grid point. Both the curl and divergence change sign several times during the experiment. The curl shows a 2-day period of high rotation; and a two-day period of upwelling could also be observed. Absolute values of the linear (local) and nonlinear (advective) acceleration are compared. For tidal motions, the linear terms exceed the nonlinear, but generally, this is not the case for currents on the considered scales.