An investigation of meteorological effects on currents in the shelf and continental slope seas northwest of the U.K. II: relationships between currents at different locations and with other variables

This report conerns data from the continental shelf and slope northwest of the UK in the period 19th August 1982 to 23rd march 1983, notably from the Continental Slope Experiment (CONSLEX). Irt develops from previous analysis for individual current meter moorings (the subject of an earlier report I) to consider wider groupings of data. These include spatial structure across current meter moorings, and relationships between currents and other variables - temperature, bottom pressure, sea level and meteorological variables. The treatment is prncipally in terms of three frequency bands (low-, band- and high-pass) covering the ranges: below q/3 cpd; 1/2 - 5/6 cpd; above 1 cpd (the corresponding filters sum to unity). These bands respectively include: most of the energy; a few spectral peaks; wide-spread rotary near-diurnal oscillations. Correlations, co-spectra and principal component structure are considered for the whole duration of the time series, and for events (slope current reversals, strong current or temperature fluctuations, occurrences of strong near-diurnal oscillations. Currents on the shelf showed extensive coherence inter alia and with meteorological variables, especially at low frequencies, for which therre was coherence with alongshelf wind, coastal shelf-break bottom pressure. These pressure variables were also extensively correlated with north/northeastward phase propagation and coherent with alongshelf wind at low frequencies. Currents over the slope in 500m were principally aligned along the slope but less coherent with each other. In 1000m or more there was still less coherence, and rotary motion suggested eddies in the Faeroe-Shetland Channel. Bottom pressure transferred from ocean to shelf-edge at higher frequencies and from shelf-edge to coast, allowing for correlated winds. Additional coastal variance prevents inference of oceanic bottom pressure therefrom. 'Mean' currents were (statistically) stronger to the north/northeast about 3 days after neap tides, by an amount (2cm/s) not clearly related to mean flow strength