Physical Oceanography 
System Nordsee 
25 
gions. These patterns, in essence, were reflected in the wind sea distributions, too. At 
8.9 m/s, mean wind speed in the central North Sea was substantially higher than in 
the German Bight because high wind speeds were about 35 % more frequent. Wind 
sea on average was 1.3 m, which was 0.3 m higher than in the German Bight. Mean 
significant wave heights (including swell) in these areas had a similar ratio of 
2.1 : 1.5 m. Peak wind speeds and wind seas were associated with SW - NW winds, 
which is typical of the North Sea. Maximum wave heights in the German Bight with all 
directions considered were generally lower than in the central North Sea, except for 
waves from W. The cause is mainly shorter wind fetch, shallower depths, and lower 
wind speeds. 
All results are based on model computations. 
Sea level (p. 104 sqs.) 
Cuxhaven, located at the mouth of the river Elbe which opens to NW, has historically 
recorded the highest water levels and most severe storm surges in connection with 
NW winds, and the lowest levels with winds from the opposite direction (SE). There 
fore, the monthly deviations of high and low water levels from climatological values are 
closely related to anomalies in the frequency of NW weather types. The increased oc 
currence of such weather types in January and from May through August 2005 led to 
above-average water levels. 4 of the 5 storm surges were caused by hurricanes during 
the 3-week storm period at the beginning of the year. During the most severe storm 
surge on 20 January, the water level rose 343 cm above MSL. 
The temporal evolution of high and low water levels since 1970 has shown that, prior 
to 1988, exceptionally high water levels occurred almost exclusively in autumn, but 
since then preferably during the winter months (Loewe et al. 2006). Trend analyses 
were carried out using Q4 surge levels as a storm surge proxy. These surge levels 
were defined as the arithmetic mean of the upper 25 % of the high water levels of any 
one season sorted in ascending order. The decrease of autumn surge levels by just 
under 20 cm in the period from 1970 to 2005 was accompanied by a 50 % reduction 
of storm frequency in the North Sea region. Until the early 1990s, Q4 surge levels in 
winter had risen by 40 cm. Owing to the comparatively slow downtrend in the time 
thereafter, the current (2005) net increase as compared to the early 1970s is about 
30 cm, although the frequency of winter storm events in the North Sea region has 
dropped to the level of the early 1970s within the same period. This discrepancy is pos 
sibly due to the large-scale storm criterion used, for results presented by von Storch 
and Weisse (2008) are indicative of the main storm corridor having shifted in such a 
way that the southern North Sea continues to be affected by rather large a number of 
storms. 
Temperature (p. 111 sqs.) 
From March to August 2005, the monthly geographic SST distributions showed but mi 
nor departures from climatology (1971 - 1993). By contrast, winter and autumn were 
characterised by strong large-scale heat anomalies, with temperature deviations in 
creasing from NW to SE, intermittently reaching up to 3 К in the German Bight. Spa 
tially averaged SSTs in winter (DJF, 7.8 °C), autumn (SON, 13.2 °C) and November 
(11.5 °C) rank 3rd, 2nd, and 1st, respectively, in the period from 1969 to 2008. With an 
annual mean SST of 10.5 °C, 2005 ranks 11th among the warmest years on record.