Meteorological factors contributing to negative surges 
27 
500 
490 
480 
470 
E 460 
_o• 
| 450 
v_ 
o 
| 440 
430 
420 
410 
400 
- - - Warnemünde — 1 Kotobrzeg 
Fig. 4.3. Variation of sea levels in Kotobrzeg and Warnemünde during a long high-pressure spell in February 1954 
FEBRUARY 1954 
4.4. Co-occurrence of atmospheric 
situations over Europe 
and negative surges at the 
southern coast of the Baltic Sea 
A major fall of water levels along large sections of 
the Baltic coast can only occur if strong offshore 
winds push water masses from the shore toward 
the open sea. Therefore, negative surges usually 
occur during the most dynamic atmospheric 
conditions, which are characterised by active, 
windy weather systems. This includes all anemo- 
baric situations with a strong westerly air flow 
component over the Baltic Sea and the north 
eastern parts of central Europe, i.e. zonal circula 
tion types and mixed circulation types. These 
circulation types are characterised by successive 
atmospheric disturbances tracking rapidly east, 
whose wind field generates gale-force winds on 
all Baltic Sea coasts, both offshore and onshore. 
The frequency of these atmospheric circulation 
types is about 55 %. The remaining 45 % is a 
group of atmospheric types containing meridi 
onal and considerable easterly components of air 
flow. Their weather systems typically are more 
stationary and usually sustain steadier winds, 
even when they reach gale force. 
To specify and calculate the frequency of co-occur 
rence between negative surges and particular at 
mospheric situations in the years 1955-2005, the 
calendar of atmospheric situation types over 
Europe by P. Hess and H. Brezowski was used. 
In addition, a comparison was made with the av 
erage surface pressure charts by G. Cawley. In 
this way, it has been possible to identify particu 
lar features of the individual atmospheric situa 
tion types which generate low sea levels. 
In the classification by Hess and Brezowski, 
30 different atmospheric situation types are dis 
tinguished. In 11 of these situation types, the 
westerly (zonal) component of air flow is predomi 
nant or at least present over central Europe. The 
different types are: Wa, Wz, WS, WW, SWa, SWz, 
NWa, NWz, HM, BM and TM (Fig. 4.4. a); they 
account for the above mentioned 55 % of all at 
mospheric situations over central Europe in the 
time from 1955 to 2005. We divided the meridi 
onal situations into two groups, the first group 
encompasses Na, Nz, HNa, HNz, HB, TrM, TB, 
TrW, and U and accounts for 27 % of all atmos 
pheric situations. The second group with the 
remaining 18 % of all atmospheric situations 
includes NEa, NEz, HFa, HFz, HNFa, HNFz, SEa, 
SEz, Sa and Sz.