Nordseezustand 2003 
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Anhang C: Mishmash Climate 
The regime character of North Sea SST is placed in the context of atmospheric circu 
lation changes. 
The temperature climate of the North Sea is characterized by long-lived quasi-stable 
cold and warm regimes that are separated through sudden shifts. Evidence is pro 
duced that SST regimes are manifestations of intra-annual monsoon-like shifts in the 
wind climate, while spontaneous reversals in SST regimes are accompanied by a 
semi-annual phase shift in seasonal wind characteristics. Specifically, the latest cold 
regime (1978 - 1987) was sustained by a wind regime that alternated between conti 
nental in winter and maritime in summer. By contrast, the recent warm regime is main 
tained by maritime winds in winter that give way to continental winds in summer. 
For lack of a better suited term for these bi-stable and hybrid climatic conditions in the 
North Sea region we call it »mishmash« climate. A sketch of the annual temperature 
swing in such climates is presented in Fig. 3-17,p. 71. 
C.1 Bi-stable SST Regimes 
A stunningly long run of positive SST anomalies has continued since June 2001. This 
gave rise to a close inspection of the time series of monthly North Sea SST that was 
derived from BSH's weekly SST analyses (www.bsh.de/en/index.jsp, menu: marine 
data - observations - sea surface temperatures). Serial monthly SST anomalies are 
displayed in Fig. 3-18,p. 72 as departures from the 1971 - 1993 base period means for 
2 consecutive 16-year periods. 
Perhaps the most important and just as striking feature is the regime character of SST 
anomalies, i. e. the persistence of positive and likewise negative departures from nor 
mal for extensive periods of time. The current warm regime shown in the upper frame 
of Fig. 3-18, p. 72 was preceded by a cold regime of comparable length which again re 
placed a moderately warm regime in the mid 1970s. 
Under the sensible constraint of 3 regimes during the period of observation, their re 
spective lengths in time may be determined by maximizing E|A(Ri)|, where A(Rj) de 
notes the mean anomaly of regime i. This procedure yields 
maxX|A(Ri)| = 0.24 + 0.36 + 0.51 = 1.11 K 
and December 1976 through August 1987 for the duration of the cold regime. 
Instantaneous termination and onset of adjacent regimes do not appear as unbear 
able idealizations in comparison to actual short term regime shifts. In any event, there 
is nothing that could be called a gradual or even linear evolution in SST (or SST anom 
alies). Instead, what is observed are irregular fluctuations about discernible quasi-sta 
ble states or levels - viz. A^), A(R 2 ), and A(R 3 ) - and spontaneous jumps and 
drops from one level of excitation to another. 
As was verified from the SST record of Helgoland Roads, the alternation of cold and 
warm regimes extends through at least the past 130 years. The current warm regime 
turns out as the most intense and longest warm period since the 1870s (Loewe et al.