Current profile measurements from the sea surface to the sea bed were obtained in the northern North Sea (59°40 N, 1°00 E in water depth 120 m) between 6 September and 7 November 1991 during a stormy period. Analysis of Acoustic Doppler Current Profiler (ADCP) measurements (10-minute averages at each 8 m through depth) showed no evidence of near-surface wind-driven shear between the top two good measurements, at 34 m and 26 m below the surface, despite winds of up to 25 m/s. However, there was shear between currents measured 2 m below the surface (from a toroidal electro-magnetic sensor mounted on a pole beneath a discus-shaped surface-following buoy) and the 26 m ADCP cell. This 2-26m shear reached values as large as 0.3 m/s and was found to correlate with the wind speed. The largest such shear occurred during an exceptionally severe storm, 16 - 19 October, when waves generated by strong northerly winds had significant wave heights exceeding 10 m. Rotary cross-spectral analysis showed high coherence between the velocity differences and the wind, at low frequency. The amplitude ratio of 2-26m shear to the wind speed was 0.0075; the direction of shear was 25° to the right of the wind. For a shorter record (6 September to 11 October) from an S4 current meter suspended 5 m below a tethered toroid, the amplitude ratio (5 m - 26 m velocity)/(wind speed) was 0.003.
The measurements also showed autumnal deepening of the seasonal thermocline, especially when a storm combined with inertial oscillations. A model with an explicit calculation of turbulence was applied to the period, and showed the overall deepening of the thermocline but significant departures of detail. The observations showed rapid deepening under a combination of strong wind/wave forcing and oscillatory shear across the thermocline; the oscillatory shear may result from a previous episode of wind-forcing.