14 
3.2 Daily reference sea level value 
This one-dimensional parameter in cm represents the influence of the actual averaged sea 
level of the whole Baltic Sea on sea level values along the southern coasts. The formula of 
this parameter is based on the air pressure differences on particular cross-sections of the 
Baltic Sea, air and surface water temperature differences, wind directions, and on the season 
(cold, warm). The formula was developed empirically by Malihski at the end of the 1960s. 
The value of this parameter is calculated daily at the Hydrological Forecasting Office in 
IMGW Gdynia. Among other purposes, this parameter is used to indicate the beginning of a 
storm surge. The daily reference sea levels for each storm surge investigated are listed in 
Table 1.1., and their frequency distribution in Fig. 3.4. An analysis of the maximum and mean 
values of this parameter (Kowalska, 1997) indicates an increase in the mean value in 1980, 
which was probably due to prevailing westerly air flow during this decade. The maximum 
values of the daily reference level occurred in the autumn-winter season. During nearly 50% 
of the surges this parameter was as high as 521 to 550 cm. During 23% of the surges it 
oscillated between 491 and 520 cm, and a parameter below 490 cm was observed in only 
3% of the surges. Low values (below 510 cm) of the daily reference sea level during a storm 
surge may indicate that the dynamics of the surge was very high, involving in particular a 
rapid rate of increase of the water levels. On the other hand, very high values of this 
parameter (e.g. above 550 cm) even before the maximum may suggest that winds in the 
vicinity of the tide gauge may not be very strong or there may be no wind at all. 
Comparing the two observation periods of 1950-1975 and 1976-2000, one can prove that 
storm surges in the latter period were more frequent at daily reference level ranges of 511 - 
530 and 551 - 560 cm respectively, and at the extreme value of the parameter, i.e. above 
560 cm. The value of 555 cm was surpassed in only 5% of all storm surge events. 
dailv reference sea level in cm 
□ 1950-1975 □ 1976-2000 
Fig. 3.4. Frequency distribution of the daily reference sea level values in cm on the storm 
surge days