5 
Tidal and Residual Currents in the Northern North Sea 
Observations 
Holger Klein, Wolfgang Lange and Ekkehard Mittelstaedt 
UDC 551.466.78:551.466.75 
Summary 
One-month current and water-level time series from the northern North Sea are analyzed with re 
gard to residual flows, volume transports, and tidal constituents. The data originate from the NORA and 
MO YENS field programs (along 59° N, July/August 1990 and roughly 62° N, September/October 1986 re 
spectively). With regard to the residual flows, the results generally confirm the known circulation pattern of 
the northern North Sea. Differences between these and other investigations are due to the great short and 
long-term variability of the current systems. The main objective of this paper, however, is to describe tides 
and tidal streams. Firstly, we relate the tidal streams along 59° N to the spring and neap high waters at Aber 
deen; secondly, up to 17 tidal constituents are determined by means of harmonic analysis. 
Gezeiten und Restströme in der nördlichen Nordsee: Beobachtungen (Zusammenfassung) 
Einmonatige Strömungs- und Wasserstandszeitserien aus der nördlichen Nordsee werden hinsicht 
lich der Restströme, Volumentransporte und Gezeiten analysiert. Die Daten stammen aus den beiden Meß 
programmen NORA entlang 59° N (Juli/August 1990) und MO YENS entlang ca, 62° N (September/Ok 
tober 1986). Die berechneten Restströme entsprechen dem bekannten generellen Zirkulationsmuster in der 
nördlichen Nordsee. Im einzelnen auftretende Abweichungen zu anderen Untersuchungen haben ihre Ur 
sache in der starken Variabilität der Restströme in diesem Seegebiet. Hauptanliegen dieser Arbeit ist die 
Darstellung der Gezeiten und Gezeitenströme, Im ersten Schritt werden die Gezeitenströme entlang 59° N 
zu den Spring- und Nipp-Gezeiten in Aberdeen in Beziehung gesetzt. In einem zweiten Schritt werden mit 
Hilfe der harmonischen Analyse die Koeffizienten von bis zu 17 Partialtiden berechnet. 
1 Introduction 
The water exchange across the northern boundary of the North Sea is dominated by the in- and outflow 
through the Norwegian Trench. The trench is the main link between the shallow North Sea and the deep At 
lantic Ocean. The transition zone between the shelf and the deep sea is also the northern boundary of several 
numerical North Sea circulation models. A main problem in modelling is posed by the great length of the 
open northern boundary of the North Sea, together with the great variability of volume transports in several 
time scales. Most of these models use only the M 2 tidal elevation. Higher tidal harmonics, however, are also 
important for North Sea dynamics and are generated on the shelf itself (cf. D e 1 h e z and Martin [1992]). 
Besides discussing tidal and residual currents, we therefore also determine tidal constituents which could be 
used to improve the boundary information for circulation models. The results of two field experiments are 
discussed below. 
Methods: 
During the NORA experiment (Nord Rand, northern boundary), 8 current meter moorings, each 
equipped with 3-5 Aanderaa RCM4/5 current meters, were deployed along 59° N between 2° W and 
4° 45’ E (N1-N8 in Fig. 1). The moorings were maintained for about one month from 15-17 July until 
18-21 August, 1990. 
The MO YENS moorings (Model Verification North Sea) were deployed between 6 and 8 September 
1986, and recovered between 15 and 19 October 1986. The MOVENS moorings (M7-M10 in Fig. 1) were