In Hamburg more than 300 people died as a result of a storm surge as recently as February 1962, even though the city is 100 km from the sea. Since then, all the dikes along the German North Sea coast have been raised; thanks to this action, the highest storm surge ever recorded (January 1976) caused only minor damage. An analysis of all historical surges

(Hewer 1980) showed that these extreme events fall into two classes: • ‘Static’ type: low pressure track Iceland – northern North Sea – Scandinavia; extended, cold low; a long-lasting but not necessarily extreme wind pushes SP600125 purchase water into the German Bight. The most prominent example: 17 February 1962. In a numerical investigation both these historical surges were modified (by changing wind amplitudes and phases somewhat, but within what is physically possible) with the aim of achieving more dramatic effects (Hewer 1980). The results are shown in Figures 14 and 15. According to these studies, the maximum sea levels recorded in the inner German Bight up till now could 3-Methyladenine datasheet be exceeded by 2.54 m for the static type and 1.70 m for the dynamic type. The long-term heat budget of the North Sea has been analysed using decadal simulations of HAMSOM (Pohlmann 2003). First, the influence of wind and atmospheric heat fluxes was studied. Surprisingly, it turned

out that the correlation of maximum wind stress and maximum monthly total heat content is nearly zero. The logical expectation would be that a stronger wind deepens the upper thermal layer, thereby enlarging the heat content of the water body. This

is explained by the negative correlation of the wind stress and the maximum sea surface temperature SST. As a matter of fact, in the North Atlantic system a warm summer is connected with weak winds (and vice versa), which means a damping of interannual fluctuations 5-FU research buy in the heat content. Nevertheless, a clear correlation (0.75) exists between the maximum heat content in summer and the minimum SST of the preceding winter. This can be explained as follows. In winter the water column is vertically mixed resulting in an almost homogeneous temperature distribution (equal to SST). During the formation of a thermal upper layer in spring/summer the bottom water is decoupled from ongoing surface processes in broad regions of the North Sea. A real interaction happens again only in the following winter. In this way the winter SST can influence the heat content in the following summer. The conservation of the winter bottom water temperature in the central and northern North Sea is one of the rare hydrographical phenomena with a ‘memory’ scale of one year. Normally, typical spin-up periods (within these the preceding dynamic state is lost) amount to only a few days in the shallow North Sea. In the cited paper (Pohlmann 2003) the interannual variability of the North Sea’s heat content was also simulated for the years 1982–1998 (Figure 16).