48 
Negative Surges in the Southern Baltic Sea 
5.13. February 1990 
Meteorological situation 
Europe had been under the influence of westerly 
and southwesterly air flow for several days, 
which freshened over the Baltic Sea and tempo 
rarily reached gale-force. 
Early on 26 February, an active depression of 
963 hPa appeared west of Scotland. Moving 
rapidly east, it reached the entrance to the 
Skagerrak around noon, slowing down: southern 
Sweden was reached at 18 UTC on that day, and 
the Alands Islands as late as about 06 UTC on 
27 February. There, it nearly stopped, with its 
deepest pressure of 939 hPa recorded at 09 UTC 
on 27 February. The depression was exception 
ally dynamic despite its rather slow movement. 
It was preceded by a large field of intensive nega 
tive-pressure tendencies, locally over -13 hPa/3 h. 
An intrusion of cold Arctic air streaming into the 
southern peripheries of the depression in the rear 
of the cold front forced an increase of air pres 
sure. The positive tendencies behind the cold 
front locally exceeded 15 hPa/3 h. In conse 
quence, a very steep pressure gradient formed 
over an area extending from the English Channel 
across the southern coast of the North Sea and 
the total area of Jutland to the Baltic Sea. 
The wind field development followed the pres 
sure pattern. From noon on 26 February, the 
intensity of the southwesterly wind increased, 
exceeding 8-9 Bft in the Kattegat and over 
Denmark. In the afternoon of that day, the heavy 
storm spread eastwards: in the Danish Sounds 
and in the southern part of the Baltic Sea, it 
increased to 11 Bft and became gusty as cold 
Arctic air flowed into the area. In the morning of 
27 February, the storm continued unabated but 
veered to westerly alongshore and slightly 
onshore directions, spreading across the entire 
area of the Baltic Sea from the Kattegat to 
Palanga, and from teba to Gotska Sandòn. 
Hydrological response of sea level 
On 26 February, the increasing southwesterly 
storm caused sea levels to oscillate irregularly 
around the mean values. Sea levels did not begin 
to fall until late in the evening: more rapidly in the 
westernmost part, at Wismar, and slower 
towards the east. As water levels fell, they con 
tinued oscillating in line with the changing direc 
tions of the gusty offshore to alongshore storm. 
The decrease was rather uneven at all gauges of 
the coastal area, so that the lowest values were 
recorded at different times at the particular 
stations. The variation curves were flat. In Wis 
mar, for instance, a sequence of very low values 
was recorded between two minima: the first mini 
mum of 395 cm occurred at 02 UTC, and the 
second one, 394 cm, at about 08 UTC. 405 cm 
was never exceeded between these two read 
ings. In Warnemünde, the highest levels recorded 
for 7 consecutive hours were 414 cm at 03 UTC 
and 412 cm at 10 UTC, with the minimum of 
398 cm recorded at 07 UTC. 
At Sassnitz, the minimum of 403 cm was re 
corded at about 04 UTC, Swinoujscie 407 cm at 
03 UTC, and Kotobrzeg 443 cm at about 05 UTC. 
Water levels did not begin to rise more steadily 
until 10 UTC on 27 February and had nearly 
returned to the mean values by evening.