Compilation of Summaries 
24 
System Nordsee 
calmer weather conditions in February and March. As directional stability and residual 
currents in both seasons were considerably weaker than the year before, there was no 
clear contrast to the diffuse current pattern that is typical of spring and summer. 
Analyses of volume transports through the Strait of Dover, the Kattegat, the western 
part of the northern North Sea boundary and the western boundary of the German 
Bight showed that inflow conditions prevailed here in 2005 on monthly and seasonal 
time scales. On all time scales considered, transports through the Channel and across 
the western boundary of the German Bight were closely coupled. Particularly persis 
tent inflow phases with high net transports of about 0.2 Sv occurred here in January, 
October, and November. Inflow through the western part of the northern boundary 
reached 2-4Sv during gale-force winds in January; the monthly net transport of 
0.4 Sv was at a similarly high level as in the stable inflow phase from June to Novem 
ber. Conditions in the eastern part of the northern boundary were characterised by wa 
ter transports in the opposite direction on monthly and longer time scales, and thus 
tended to compensate those through the western section. 
The sequence of daily current patterns in the German Bight is documented in the cur 
rent calendar. In 2005 (2004), cyclonic circulation was recorded on 135 (160) days, an- 
ticyclonic states on 65 (71) days, and variable circulation patterns on 88 (77) days. The 
decrease in rotational patterns was compensated mainly by an increase in directional 
flow (77, 58), about 3/4 of which was directed N (13), NW (32), and W (14). The pre 
dominance of cyclonic circulation patterns was particularly pronounced in January 
(frequent storms) and in October / November, when this pattern persisted for 16 con 
secutive days due to incessant SW winds. However, circulation patterns in general 
were less persistent than in the preceding year, with variable and directed patterns typ 
ically representing transitional forms of short duration. 
The dependence of circulation patterns on large-scale weather types was confirmed 
in a contingency analysis. The anticyclonic pattern is associated with high-pressure 
and NW weather types, the variable pattern with the same weather types but weaker 
winds. SW weather types generate almost exclusively cyclonic current patterns, 
whereas SE weather types induce predominantly N or NW directed patterns. 
Waves (p. 93 sqs.) 
Waves are wind-induced perturbations of the sea surface. The wave climate in 2005 
was characterised by seasonal geographic distributions of significant wave height and 
direction of wind sea and swell. Typical wave distribution patterns are determined by 
prevailing wind conditions and by the geography and bathymetry of the North Sea. Be 
cause of frequent gales in January, mean wave heights in winter 2005 exceeded those 
in the 2003 and 2004 winter seasons, when winds were weaker. The mean wind and 
wind sea directions in all seasons were westerly, while swell came from NW throughout 
the year. Although the mean and maximum wave heights at representative positions 
exceeded those of the preceding year, they were still below the climatological values. 
During hurricane >lngo<, significant wave heights of about 10 m were recorded in the 
northern and central North Sea on 20 January. On 12 January (hurricane >Gero<), 
wave heights in the northern North Sea even exceeded 12 m. 
The distributions of wind direction in the central North Sea and German Bight are typ 
ically bimodal. The frequency peak at Ekofisk was in the NW sector, and a secondary 
peak mostly in the S sector. Corresponding maxima in the German Bight were found 
shifted towards W and E, respectively. In autumn, southerly winds prevailed in both re