Atle Ommundsen

A high resolution tidal model for the area around The Lofoten Islands, Northern Norway

A depth-integrated numerical model with grid resolution 500 m has been used to simulate tides around the Lofoten Islands in northern Norway. The model spans more than 31 latitude and covers a sea area of approximately 1:2 � 10 5 km 2 : The fine spatial resolution resolves the important fine scale features of the bottom topography on the shelf and the complex coastline with fjords and islands. Boundary conditions at the oceanic sides of the model domain are obtained by interpolation from a large-scale tidal model covering the Nordic Seas and implemented with the flow relaxation scheme (FRS). The semi-diurnal components M2; S2 and N2 and the diurnal component K1 are simulated. Harmonic constants for sea level are compared with observations from 21 stations. The best fit is found for the M2 component with a standard deviation between the observed and modelled amplitude and phase of 2:3 cm and 2:51; respectively. The standard deviation for the other smaller components ranges between 1.5–2:8 cm and 5.3–16:71: Current fields from the model are compared with observations in four locations: the Moskenes sound,the Gims y channel,the Tjeldsund channel and the Sortland channel. In the Sortland channel,the model predicts a dominant diurnal K1 current in agreement with observations. r 2002 Published by Elsevier Science Ltd.

Idealized model simulations of barotropic flow on the Catalan shelf

Abstract The effect of along shelf variation in shelf width on barotropic shelf edge flows and topographic shelf waves are investigated with a numerical model. The model topography represents a gradual transition from a narrow straight to a broader straight shelf region. It is designed primarily to model the Catalan shelf on the northeastern Mediterranean coast of Spain, but the results obtained here are of general validity and will also apply to shelf flow under similar conditions elsewhere. The numerical experiments are carried out with flow imposed, both steady and oscillatory, at the upstream end of the narrow shelf region. With a prescribed shelf edge flow there is a strong tendency for topographic steering in the transition zone. The adjustment is found to take place on a short time scale of 2–5 days set by propagating wave modes rather than by advection. Bottom friction effects do not lead to significant on-shelf leakage of the flow. Flow instability and eddy formation are found to occur, even in cases where the potential vorticity for the imposed flow does not have a local maximum on the shelf slope. The instability leads to development of anticyclonic eddies on the narrow shelf which undergo strong non-linear adjustment at the transition zone from a narrow to a broader shelf. On the broad section of the shelf near the transition zone there is a tendency for formation of a large anticyclonic eddy. Bottom friction is found to influence the flow instability and the formation of eddies in cases where the flow is marginal for instability and growth of eddies. Particle tracking has been performed in order to study cross shelf mixing and transport. Finally, we have studied the current response due to a concentrated wind stress jet acting perpendicular to the coastline in the transition zone between the narrow and the broad shelf regions. A dipolar eddy structure is found to develop with the axis of the dipole tilting about 30° with the axis of the wind jet and with strong current shear in the zone near the dipole axis.

Sources of the Maelstrom

The Lofoten Maelstrom on the northern coast of Norway has been renowned for centuries for its strength and dangerous whirlpools. We now complete a previous review of the historic literature about the Maelstrom and present results of simulations describing the large-scale dynamics of this remarkable phenomenon.

Models of cross shelf transport introduced by the Lofoten Maelstrom

Abstract The drift of particles released in the tidal current (Moskstraumen) near Lofotodden, located at 67°50′N, 12°50′E, has been studied. The periodical tidal current combined with a background current is found to introduce a transport between Vestfjorden inside Lofotodden and the shelf outside. This particular transport may be important for the drift of cod eggs, larvae and other important biological and chemical tracers. A fine-resolution numerical model provided the Eulerian tidal current field based on which the particle trajectories are calculated using a Lagrangian particle tracking technique. The tracking algorithm was extended by a random-walk method to simulate small scale turbulence. An idealized current model of the area is also developed for use as a simplification tool to reveal the basic mechanisms of the drift and to demonstrate the sensibility of time stepping in numerical integration.

Implementation of High Resolution Tidal Current Fields in Electronic Navigational Chart Systems

A system for displaying tidal currents in an electronic chart display and information system (ECDIS) has been developed and implemented in compliance with the standards of the International Hydrographic Organization (IHO). The tidal current fields can be displayed in real time on the electronic navigational chart and several options and functions for updating and zooming have been designed. The current fields are calculated from a data base with the harmonic constants for the four major tidal constituents. The harmonic constants are obtained from a high resolution numerical model with horizontal grid resolution of 100 m. The model is validated by comparing with sea level and current measurements. The depth matrix for the central part of the model domain was calculated from data from multibeam bathymetric surveys. An application example of the implementation is given for Trondheimsleia, a part of the main sailing route along the western coast of Norway.

Veikimorener i Finnmark, Nord-Norge

A numerical model with grid resolution 500 m has been used to simulate tides on a section of the shelf off the coast of Møre and Trøndelag in western Norway. The model spans c. 3° latitude and covers a sea area of c. 8.104 km. The fine spatial resolution resolves important fine scale features of the bottom topography on the shelf and the complex coastline with fjords and islands. Boundary conditions at the oceanic sides of the model domain are obtained by interpolation from a larger scale tidal model covering the Nordic Seas. The semi-diurnal components M2, S2 and N2 and the diurnal component K1 are simulated. Harmonic constants for sea level are compared with observations from 28 stations. The standard deviations between the observed and modeled amplitudes and phases for the dominant semi-diurnal component M2 are 1.7 cm and 4.8–7.0° respectively. Current fields from the model are compared with measurements from stations along the pipeline from Tjeldbergodden on the coast to the oil and gas fields on the northern rim of Haltenbanken. Parameters, particularly for the M2 current ellipse, are found to be in good agreement with measurements.