Vertical structure of horizontal currents and vertical velocities observed off the Estonian coast using a recording Doppler current profiler

Abstract

. The 3D current structure was studied in Muuga and K(cid:252)dema bays using RDCP 600 current profiler data from autumn 2003 and early summer 2004. Altogether 245 hours of flow measurements from up to nine depth layers were obtained. Despite calm weather conditions (average wind speed 3.4 m/s during the three measuring periods), the maximum horizontal current velocity reached 37 cm/s. As all the mooring sites were relatively close to the coast, downwind horizontal transport with relatively small differences over the vertical profile prevailed. The average modula of vertical velocities were between 0.47 and 0.60 cm/s, being 10(cid:150)20 times smaller than the simultaneous horizontal velocities. This may suggest that at least above sloping bottoms and within the upper 10(cid:150)20 m layer, rapid vertical spread of both hydrochemical and hydrobiological properties is hydrodynamically favoured. However, higher than expected measured vertical velocities indicate a disagreement with certain theoretical considerations. The possibility that the particles backscattering the RDCP signals were not neutrally buoyant should be investigated in detail in the future.