Dt. hydrogr. Z. 44. 1991/92. H. 3. Kleine! ul.. Ciments; German Bight
139
4 Local currents under a violent storm
The violent storm from January 25/26, 1990, markedly influenced the flow front the
surface clown to the bottom. The wind speed exceeded 60 kn (12 bit) for nearly 12 hours, the
prevailing wind direction was 220° to 230° (see Fig. 2). The bold vectors in fig. 3 represent
the hourly averaged current at 1 mab, related to high water at Norderncy on January 25 at
21 :41 UTC. Within a few hours after the onset of the storm the near-bottom currents in the
troughs approximately followed the local wind direction. At the ridge crest the current at 1
maberossed the ridge nearly perpendicular. Progressive vector diagrams indicate, that the strong
slonn-induccd eastward currents suppressed the directional alternation of the tidal currents for
more than 20 hours (Fig. 6).
Table I compares the vertical energy distribution of the currents during the storm-period
and during a calmer period. Shown arc data from mooring K2, L3. and from the “Rhonrad”
R, averaged over 24.5 hours. The first averaging period runs from January 21 to 22 with wind
speeds between 20 and 30 kn (5 to 7 bfl). The second period includes the violent storm. The
positions of the three moorings are not more than 400 m apart.
Table I
Vertical distribution of current speeds and energies
mab
'niax
V
V
SF
^ H
e/^'m
SI
m
cm/s
cm/s
cm/s
7o
7 « 7
Cirr/S"
*7 , 7
enr/S"
-
min
-
January 21
00 : 00 -
-January 22 00 :30,
1990, wind: 5 to 7 bft
18.0
196
107
39
37
5885
774
7.6
2
L3
12.0
56
38
4
10
738
7
105.4
2
K2
1.0
28
18
< 1
1
165
< 1
1646.0
2
K2
0.3
28
13
3
21
104
4
26.0
1
R
January 25 1
1 8 : (10 -
January 26
18: 30, 1990, wind
1: 10 to 12
bft
18.0
247
115
100
87
2823
5039
0,6
2
L3
12.0
102
73
45
61
1716
1022
1.7
2
K2
1.0
78
43
29
67
588
425
1.4
2
K2
0.3
56
16
2
13
216
216
1.0
1
R
mab = metres above bottom, v= scalar mean speed. v=mean vector speed, SF = (v/v) * 100,
k M = mean kinetic energy, k E = eddy kinetic energy, SI = sampling interval
