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5. TYPES OF ATMOSPHERIC PRESSURE PATTERNS AND WIND FIELDS INDUCING 
STORM SURGES 
As in all semi-enclosed, nearly tideless marginal seas, oscillations of coastal water levels are 
caused mainly by the impact of strong winds on the surface water (Wielbinska 1964, Malicki, 
Wielbinska 1992, Sztobryn et al. 1995, 2001, Stanislawczyk 2002). The wind accompanies 
an atmospheric disturbance moving across the sea or in its vicinity. During onshore winds, 
the sea level rises due to wind set-up, while strong offshore winds cause a considerable 
lowering of coastal sea levels. In an area that is influenced by an active atmospheric system, 
e.g. a low-pressure system with a small radius, wind field directions in front of the system 
and in its rear may be diametrically opposed. When such a depression is moving along a 
particular coast, two different coastal sections - sometimes less than a hundred kilometers 
apart - may simultaneously suffer the impact of stormy winds from opposite directions. The 
zone of such sharp wind shear, usually along an occluded front, moves along with the 
advancing depression. Other types of pressure pattern produce stormy wind fields in which 
the wind directions change less rapidly. 
The southern coastal waters of the Baltic Sea are mostly exposed to direct wind set-up 
caused by stormy winds from the W-NW to E-NE sector although, depending on local 
morphometric conditions, other directions must be taken into account as well. The western 
sections of this coast are more sensitive to sea level oscillations than the areas east of the 
Odra estuary. 
In this monograph, only the sea level wind set-ups between Wismar and Kotobrzeg in the 
years 1976-2000 have been considered. During this period, 73 storm surges in this coastal 
area were classified as wind set-up surges. In 17 of these surges, at least one of the water 
gauges indicated a culmination of 600 cm or higher. All of the surges studied were caused by 
gale-force onshore winds of shorter or longer duration, with a prevailing northerly component 
of the wind direction. Several types of pressure pattern were identified that had caused these 
winds. 
5.1 Northerly air flow over Scandinavia and the Baltic Sea 
When an anticyclone located above the British Isles spreads towards Scandinavia and tends 
to track farther east, low pressure centres travel southwards along a route leading from the 
extreme northeast of Scandinavia along Finland towards western Russia. The pressure 
gradient over the Baltic Sea becomes steeper, and the northerly air flow gradually increases 
in force and gustiness. During the development of this pressure pattern, there are temporary 
fluctuations of the wind speed resulting from alternating pulsations of the pressure gradient 
on the edge of developing anticyclones. Besides, disturbances develop in the form of 
secondary cold fronts in the intensive inflow of air. They tend to deform the uniform air flow: 
northerly winds preceding the front briefly back NW - W, sometimes even SW, and veer N 
again behind the front. 
With the above pressure pattern, winds usually reach gale force when northerly directions 
have been established in the whole area, exposing the entire southern Baltic coast to a 
strong onshore storm with resulting wind set-up. All water gauges normally indicate a gradual 
increase of sea level, though oscillations are probable. 
Examples of this pattern are the storm surges of 11 April 1997 and 17-18 January 2000. 
Deviations from the above pressure pattern occur when depressions travel southeast across 
the Baltic Sea or across land along the Baltic east coast towards the Russian plains, with a 
high-pressure ridge developing over Scandinavia after their passage. This pressure pattern 
is characterised by cyclonic veering of winds over the Baltic Sea and the adjacent coast in 
the initial phase. In front of the advancing depression, winds veer SE - SW in a rather large 
area, increasing in force before the frontal line that is usually connected with the low 
pressure centre. Such frontal winds veer rather sharply NW, N, and temporarily even NE. 
The whole system moves S-SE, with an intensive northerly air flow at the rear of the 
depression, and soon covers the entire area of the Baltic Sea. This phase of the storm surge,