Compilation of Summaries 
19 
and steady periods of high W-erly flow by distinctive wind shifts. The 2 nd of 
these periods sprang up with a clustering of all November gales (6) and main 
tained its stormy character beyond the turn of the year. Not only did the num 
ber of severe December gales attain a new all-time high (6), the NAO index also 
hit a never observed peak level of 2.65, which stands out in stark contrast to 
the record low value of -3.56 set one year before. At 5.9 °C in December, air 
temperature at Norderney failed to drop against the preceding month. Against 
previous year’s record amplitude (21.6 K) the descent in temperature since July 
halted to 10.0 K, a range underrun but once before (1974). 
3 Ocean Physics 
Currents (Page Seite 84 et seq.) 
The near-surface circulation of the North Sea and volume transports through 
selected transects are largely influenced by atmospheric forcing. During the 
period under report two outstanding situations had been observed: The accu 
mulation of strong westerly wind events in November 2009 induced a North 
Sea wide pronounced cyclonic circulation pattern. This is shown in the figures 
of the monthly near-surface circulation patterns and in the volume transports 
through the Dover Strait and in the German Bight. This event was followed by 
a long-lasting circulation anomaly in the northern North Sea in the winter 
2009/2010, where a three-month outflow in the area of the Norwegian Trench 
was forced by persistent easterly winds during this relatively cold winter. 
The circulation statistics for the German Bight are based on the chronological 
order of the daily residual currents which are assigned to nine typical circula 
tion patterns. The frequency distribution of the circulation patterns in the years 
2008 and 2009 is very close to the 10-year average. The lack of longer phases 
of constant cyclonic circulation, which had durations of up to 28 days in pre 
vious years, is striking in 2008. Only an 11 -day cyclonic phase at the beginning 
of September was observed in 2008. In November 2009, a 20-day cyclonic 
phase occurred and was only interrupted by one day with a northerly current. 
In 2010, there were significant deviations from the 10-year average. The gener 
ally dominant cyclonic pattern shows the lowest frequency since 2000, while 
the anti-cyclonic pattern shows the greatest frequency since 2000. A phase of 
constant anti-cyclonic circulation over 8 days is also unusual, because in the 
past longer p 
hases of a constant circulation type had always been formed by the cyclonic 
pattern. In 2011, the anti-cyclonic and directional type show a clear decrease 
in comparison to the 10-year average, which was compensated by the variable 
type. The variable type also formed the longest phase of a “constant” current 
type with 11-days duration. In this case, however, it means 11 days with no 
directional preference. 
Waves (Page Seite 101 et seq.) 
The wave climate during the period 2008-2011 was characterized by seasonal 
geographic distribution of significant wave height, wind sea- and swell direc