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The TOPEX-1 moorings were deployed on January 19. 1990. On January 25 we changed 
the positions of the moorings Kl. L 1, and L2lothc positions K1A, LIA. and L2A. During this 
second deployment period two violent storms passed the investigation area. Short (“K-”) moo 
rings had instruments at 1 and 12 metres above bottom (hereafter mab), long ("L-”) moorings 
reached up to 18 mab. Recovery of the moorings was on January 29 and 30, 1990. 
The TOPEX-II moorings (I to 8 in fig. 1). equipped with 2 or 3 Aanderaa current meters, 
were deployed from January 25 until 31,1991. The sampling depths ranged between 2 and 17 mab. 
2 Meteorological observations 
Onboard RV “Gauss” meteorological observations were recorded every two hours so that 
the local weather conditions are sufficiently documented during both experiments. During 
TOPEX-1 strong southwesterly winds between 5 and 12 bit (16 to 80 kn) were dominating. 
One day before the deployment of the moorings a strong storm had passed the area. The major 
event, however, was the violent storm from January 25/26 with wind speed up to 80 knots. It 
was caused by a 970 hPa trough westwards off Ireland on January 25. On January 26 its core 
had deepened to 950 hPa, now lying in the northern North Sea.The storm caused storm surges 
of 3.5 metres at the North Frisian coast, 2.3 metres in the Elbe estuary and 1.5 metres at the 
island of Helgoland (Nee m a n n 11990|). A second storm, caused by a 975 h Pa trough over 
the British Isles hit the area on January 28 a few hours. 
One year later, during TOPEX-II, most of the time the wind came from the northwest with 
a maximum wind force of 6 bit (27 kn). Stickplots of the local wind vectors according to 2- 
hourly observations taken on RV “Gauss” arc shown in fig. 2. 
3 Local currents under moderate winds 
The flow pattern of the TOPEX area is dominated by the semi-diurnal tides. They are 
locally characterized by strong flood currents which exceed the ebb currents by about 20%. 
The maximum Hood and ebb currents arc about 77 and 62 ern/s for spring tides and 62 and 
51 cm/s for neap tides (DH1 119881). The sticks in fig.3 represent the hourly total mean How 
at 2 mab during TOPEX-11, related to high water at Norclerncy and averaged over 8 tidal periods. 
The currents around the ridge are nearly homogeneous, there arc no significant differences 
between positions over the ridge and positions in the troughs. Only the southernmost mooring 
(7) shows a different direction. 
Fig. 4 shows the vertical structure of the How by means of ADCP-measurcmenls at the 
ridge-crest and in the landward trough (A2 and A1 in fig. 1). The vertical resolution is 1 m, 
the measurements cover the range between 3 mab and 3 m below the surface. The scalar hourly 
mean currents have been related to high water at Nordemey. At both positions the strongest 
currents occur 3.5 to 1 hours before and 3.5 to 6 hours after high water. At trough position A1 
the flood current exceeds the ebb current by about 30 cm/s (>30%). The local wind blew from 
310° to 320° (3 to 4 bft), i.e., it had the tendency to enhance the eastward Hood current but to 
weaken the ebb current. During the ADCP-measurcmenls at the crest (A2) the wind came with 
2 to 4 bft from 45° to 130°. Therefore the flood current - being normally stronger than the ebb 
current - was weakened and both currents had nearly the same strength. Generally, the near- 
bottom maximum currents at the crest are up to 20 cm/s stronger than in the troughs. 
A tidal current analysis of historical time series over the ridge at position “B” in fig. 1 
(DHI 11988j) suggests that the maximum ebb and flood currents arc focussed in a direction 
which cuts the ridge axis tinder an angle of about 20 to 30° (Fig. 5). This agrees with observations 
at sliorcface-connccted ridges about 10 miles eastwards of this area (F1 e m m i n g , [19911). 
Hourly averaged ADCP-clata from the crest position (A2), recorded at winds less than 20 kn, 
suggest basically the same directions relative to the ridge at levels deeper than 5 to 6 m below 
the sea surface.