15 
Fig. 6 Mean maximum spring (a) and neap (b) speeds in cm/s in the NORA section. 
Tide and tidal streams in the northern North Sea resemble a progressive wave; the strongest northward 
streams occur around the time of local low water, the strongest southward ones at about local HW. Slack 
water or time of minimum speed is about 3 hours before and after local HW. At 59° N, eastwards off the Or 
kneys, HW occurs about 3 hours earlier than in Aberdeen. With regard to the tidal stream figures at Aber 
deen, account must be taken of these three hours if the progressive wave character is to be recognized. 
The tidal stream at 2° E is approximately half an hour behind the tidal stream near the Orkney Islands 
at 2° W. Nearing the bottom, the rotating tidal stream becomes more and more alternating. The stream el 
lipses do not show a distinct vertical phase shift and the phase shift between spring and neap conditions is 
small (<0.5 hours). This is valid for the NORA section between 2° W and 2° E. In the Norwegian Trench, 
where the tidal streams are mostly alternating, the situation is not as clear as in areas to its west. In the case 
of rotational currents, for example near the surface at N7 and N8, the streams rotate both clockwise and an 
ticlockwise and even change their sense of rotation from spring to neap tide. In general, the tidal streams in 
the Norwegian Trench occur about one hour later than those off the Orkneys. 
MOVENS results: 
In the MOVENS area the tidal streams have considerable diurnal inequalities, so the tidal currents 
cannot be related to the semi-diurnal tides at Aberdeen or Bergen. Synthesizing the tidal streams from har 
monic constituents yields maximum speeds (speeds connected with the higher HW during spring time) of 
less than 10 cm/s in the MOVENS area. The maximum tidal stream slightly exceeds 10 cm/s only at a depth 
of 55 m at position MIO, the MOVENS station nearest the Norwegian coast. 
3.2 Harmonic Analysis: Tidal Streams 
The length of our measurements allows a harmonic analysis which resolves the 17 constituents given 
in Table 5 for the current measurement at 24 m depth at position N1. For all other time series, only those 
constituents are listed which have amplitudes greater than 1 cm/s for at least one of both stream com 
ponents. The method of harmonic tidal analysis assumes that the tide at every location is formed by the 
same constituents as the equilibrium tide, and that the periods of these terrestrial constituents are those of 
the equilibrium constituents. Every terrestrial constituent, however, lags behind its corresponding equi 
librium constituent. The phases of the equilibrium constituents at 0 hour on 1 st January each year have been 
computed for several years in advance and are published, for example, by DHI [1967]. From the phase of a 
constituent at 0 hour on 1st January and its known period, its phase can be computed for any time and day. 
The value of the constituent equals //cos (E-G), with H the local amplitude of the constituent, E the phase 
of the equilibrium constituent at the chosen time, and G the local phase lag of the constituent. H and G have 
been evaluated from the components of all NORA and MOVENS time series according to Pansch 
[1988].