Nordseezustand 2004 
21 
Physical Oceanography 
4.0 m/s from W (261°), which hardly differed from the climatological vector wind (3.7 
m/s from WSW, 256°). 
The annual cycle of global radiation on the island of Norderney was generally in line 
with climatological data. Minor surplus radiation in March, April and September was 
attributed to high-pressure weather. The seasonal evolution of air temperature on Nor 
derney was normal as well. Major positive departures occurred in April and August due 
to continental warm air advection from SE. At 16.7 °C, the mean temperature in sum 
mer (JJA) would appear cool in comparison to the »mediterranean« extremes of pre 
ceding years (2002: 17.9 °C; 2003: 18.3 °C), but in fact was close to normal, statisti 
cally. 
Physical Oceanography 
The atmospheric circulation in the North Sea region imprints itself on patterns and in 
tensities of surface currents. The characteristic current pattern is large scale cyclonic 
(counterclockwise) rotation due to prevailing winds from SW to NW. In 2004, this pat 
tern was not restricted to winter and fall, but was a prominent feature of the summer 
circulation as well. Stronger wind forcing than in the preceding year led to enhanced 
current speeds and a reduced directional variability. Unusually frequent NW winds re 
sulted in a strong northerly inflow of saline Atlantic water, while net transports through 
the Channel and the Kattegat, at 0.015 and 0.044 Sv/a, respectively, were in the nor 
mal range. 
The sequence of daily current patterns in the German Bight is documented in the cur 
rent calendar. In 2004 (2003), cyclonic circulation was recorded on 160 (150) days, an- 
ticyclonic states on 71 (50) days, and variable circulation patterns on 77 (109) days. 
The reduced frequency of variable (diffuse) circulation states resulted from a sharp fall 
in high-pressure weather types, usually associated with weak winds. The increase in 
anticyclonic current patterns, on the other hand, corresponded to an enhanced fre 
quency of NW weather types. Other close associations between current and weather 
calendar were identified. SW weather types, for instance, almost exclusively generate 
cyclonic current states. Both calendars are important tools in the interpretation of 
anomalous events in dependent state variables. 
Waves are wind-induced perturbations of the sea surface. The wave climate in 2004 
was characterized by seasonal geographic distributions of significant wave height and 
direction of wind sea and swell. In winter, summer, and fall, mean wave heights were 
up to 0.5 m higher than in the same seasons of the preceding year, when weak winds 
prevailed. Nonetheless did mean and maximum wave heights at representative loca 
tions fall short of climatological reference values. Both, wind and wind sea, on average 
came from westerly directions, except in spring. Swell was directed NW in all seasons. 
During the NW storm >Pia< of November 18, significant wave heights of about 8 m oc 
curred in the central and southern North Sea. 
Regional differences in wind forcing and wind sea were pointed out for two represen 
tative positions in the German Bight and the central North Sea. In the German Bight, 
wind and wave direction were found to have bimodal distributions (double peak); a dis 
tinct secondary peak in the E-SE sector was observed only here. The main peak at 
either position varied seasonally between SW and NW and was associated with high 
est wind speeds and wind seas. The mean wave height, at 1.4 m, was 0.5 m lower than