Analysis of current and sea level observations from Trondheimsleia

Sea level and current measurements from Trondheimsleia have been analysed and the parameters of the tidal ellipses for the major tidal components M2, S2, N SUB>2, and K1 have been calculated. Harmonic constants for sea level and tidal ellipse parameters have been compared with the corresponding data from a high resolution tidal model in order to validate the performance of the model. Short periodic oscillations with period about 40 minutes are observed at the time of peak tidal current at one station located in a channel with relatively strong tidal currents

Characterizing chaotic dispersion in a coastal tidal model

Abstract Diverse Lagrangian methods are used to study dispersion and mixing in a model in the Norwegian Trondheim fjord. We focus on the tidally driven currents, neglecting wind-forcing, and generate a large number of particle trajectories. We first consider traditional measures (absolute and relative dispersion) involving averages over all particles. We then contour those measures, to gauge the spatial variations. Then we examine a more recently developed measure, the direct Lyapunov exponent (DLE), to further refine the description of the spatial variability. The results suggest regions of strong mixing adjacent to regions with weak mixing, so that particles in nearby regions may experience very distinct evolutions. And M2 dominates the dispersion; adding additional tidal components affects mainly the amplitude of the particle excursions rather than the character of the mixing

Diagnosing ocean tracer transport from Sellafield and Dounreay by equivalent diffusion and age

A simple approach for estimating the equivalent diffusion for diagnosing tracer transport is proposed. Two different expressions are derived; one is based directly on an analytical solution of the two-dimensional advection-diffusion equation, the other uses the variance of the tracer distribution. To illustrate some features of the equivalent diffusion and possible applications thereof, idealized releases of passive tracers from the nuclear fuel reprocessing plants at Sellafield in the Irish Sea and Dounreay on the northern coast of Scotland have been simulated with a regional isopycnic co-ordinate Ocean General Circulation Model. Both continuous and pulse releases are considered; the former being representative of the actual historical discharges from the reprocessing plants, the latter resembling an accidental scenario. Age tracers are included to calculate the mean time elapsed since the tracers left their source regions. It is found that in the Nordic Seas the age of tracers from Dounreay is approximately 2 years younger than the age from Sellafield. Although tracers from both sources eventually end up along the same transport routes, significant qualitative differences regarding the dispersion properties are found. It is argued that one single parameter, the equivalent horizontal diffusion, which is estimated to be in the range of 20–56 m2 s−1 from Sellafield and 170–485 m2 s−1 from Dounreay, determines these differences