Characteristics of extreme wind wave events in the Gulf of Gdańsk and associated atmospheric conditions over the Baltic Sea

Nowadays, with possible changes in wind patterns and growing interests in the development of wind farms and other forms of renewable energy on the Baltic Sea, statistical characteristic of prevailing wave conditions at the site and changes in energy distribution, are essential. The Gulf of Gdańsk (Southern Baltic Sea) is an especially interesting area due to the presence of very characteristic long peninsula which strongly affects wave propagation and, in consequence, wave energy distribution. The objective of this work is to obtain most characteristic features of extreme storms that had significant impact on the Gulf of Gdańsk during the last half-century and associated meteorological conditions

In this study we analyse two hindcast datasets which are the result of an EU-funded project HIPOCAS (Cieślikiewicz & Paplińska-Swerpel 2008). The first one is the 44-year long reanalysis of meteorological data produced with the atmospheric model REMO (Jacob & Podzun 1997).

The second dataset used in this study is wave data produced with wave model WAM. For the modelling of waves over the Baltic Sea, a subset of gridded REMO data were extracted. Wave data have been produced in a rectangular grid in spherical rotated coordinates with the resolution 5’×5’.

The principal goal of our analysis is twofold. First, we want to estimate long-term stochastic characteristics of some basic meteorological parameters and wind wave fields. Atmospheric pressure at sea level and the wind velocity at 10 m height are analysed. As far as the wind wave data are concerned, we focus on the significant wave height (H_s), mean wave period and the mean direction of wave propagation. Secondly, this study aims to find out the characteristic features of atmospheric conditions causing extreme wind wave events in the Gulf of Gdańsk. To this end, a number of extreme storms, that are critical for a few chosen Gulf of Gdańsk regions, are selected based on H_s time series. For those selected storm periods, the storm depressions’ tracks and the overall evolution of atmospheric pressure and wind velocity fields are examined.

Our analysis showed two distinct metrological conditions that cause extreme storms in the Gulf of Gdańsk. Cyclones moving along the east side of the Baltic Sea are associated with strong northerly winds, which cause extremely high waves in the Gulf. On the other hand, cyclones travelling east in the zonal direction over the northern Baltic bring strong westerly winds. They significantly raise H_s, although not to the extent observed for the northerly winds.

In our study, we also look for the essential characteristics of the extreme meteorological conditions via results of the Empirical Orthogonal Functions (EOF) method, applied to the wind velocity vector fields.

Computations performed within this study were conducted in the TASK Computer Centre, Gdańsk with partial funding from eCUDO.pl project and the Project for Young Scientist No. 539-G210-B412-19.

Cieślikiewicz, W. & Paplińska-Swerpel, B. (2008), Coastal Engineering, 55, 894–905.

Jacob, D. & Podzun, R., (1997). Meteorol. Atmos. Phys., 63, 119–129.