Nordseezustand 2003 195 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.