Physical Oceanography 
System Nordsee 
29 
hand, circulation in the entire North Sea region now came to a near standstill, the Bal 
tic outflow, on the other hand, which had been at a low level for a long period of time, 
now formed a very strong stream flowing into the northern North Sea. Later in the year 
2007, surface circulation was mostly weak and of low persistence. 
Circulation statistics for the German Bight are based on the temporal sequence of 
daily circulation patterns of the residual currents, which show nine typical patterns. 
Compared to the year before and the year after, 2006 had a markedly lower day-to-day 
variability and clearly lower frequency of directional flow patterns, which are usually 
linked to high wind events. 
In the reference period of 2000 - 2009, the lowest frequency of cyclonic patterns was 
recorded in 2007. Although westerly storms continued almost throughout the second 
half of January, cyclonic circulation in the German Bight was interrupted by a phase 
of variable circulation. The anticyclonic circulation pattern reached a record frequency 
of 71 days (as in 2004). The particularly rare (frequent) occurrence of the variable pat 
tern in summer (autumn) is in keeping with high (low) speeds of North Sea wind in the 
particular seasons. 
Waves (p. 131 sqs.) 
Typical wave distribution patterns are determined by the prevailing wind conditions 
and by the geographic/bathymetric shape of the North Sea. Mean wave heights in 
most quarters of the years 2006 and 2007 were higher than in the preceding years. In 
all seasons, the mean wind and wind wave directions were SW - NW, except in the 
winter of 2006 when southeasterly directions prevailed. Swell had a NW direction in all 
seasons. During a NNW storm event on November 1,2006, significant wave heights 
in the northern and central North Sea exceeded 10 m, and 9.8 m was measured off 
the East Frisian coast. 
Sea Level (p. 137 sqs.) 
Since the middle of the 19 th century, water levels along the German North Sea coast 
have been measured at gauge stations. Measured water levels are referred to land- 
based geodetic survey points and, strictly speaking, provide data on relative water 
level fluctuations. 
With respect to the period from 2006 to 2007, available measurement data indicate 
that there have been no significant changes either in the tides or in the number of 
storm surges, and least of all in relative mean sea level. Any changes in tidal ranges, 
heights, and phases are taken into account in the Tide Tables issued by the BSH, 
which are published annually. The observed change in relative mean sea level is with 
in the scope of the long-term rate of sea level rise, which is about 20 cm per century, 
and the number of storm surges is slightly above the mean of the 1951 - 2007 period, 
although there have been a few years with more than twice the normal frequency. 
The number of storm surge events in any particular year is governed to a consider 
able extent by chance because a storm surge can only occur if the peak of the storm 
coincides with the tidal phase. 
Temperature (p. 142 sqs.) 
In both years, 2006 and 2007, the annual mean sea surface temperature (SST) of the 
North Sea tied the record height of 11.0 °C established in 2002. Nonetheless, this record