Analysis of meteorological regimes resulting in severe storms in the Gulf of Gdańsk

One of the most dangerous aspects of the observable climate change is an increase in frequency of severe weather events. This is true especially for the coastal regions, that are particularly vulnerable to strong winds and high waves, such as Baltic Sea which lies at the end of one branch of North Atlantic storm track, which is said to have changed in recent decades. Statistical analysis of past events can reveal whether these storms have any common characteristics which might allow for more precise prediction of occurrence of sea storms and better mitigation of storm effects.

The Gulf of Gdańsk (Southern Baltic Sea) is a heavily populated sea area with commercial harbours and long peninsula which strongly affects wave propagation and wave energy distribution. The main aim of this work was to confirm whether weather patterns, responsible for extreme storms observed in the last half-century in the Gulf of Gdańsk, have common characteristics, as was indicated by our preliminary research.

Two hindcast datasets are analysed in this work. The first one is the 44-year long reanalysis of meteorological data produced with the atmospheric model REMO (REgional MOdel; Jacob and Podzun 1997). The second dataset is wave data produced with the wave model WAM. For the modelling of waves over the Baltic Sea, a subset of gridded REMO data was extracted. Both datasets are the result of an EU-funded project HIPOCAS (Cieślikiewicz & Paplińska-Swerpel 2008).

To better distinguish similar patterns, long-term stochastic characteristics of some basic meteorological parameters (e.g. atmospheric pressure) and wind wave fields (e.g. significant wave height (H_s)) were estimated. The preliminary analysis confirmed a strong anisotropy of wind directions over the entire Baltic Sea area which seems to be stronger for stronger winds. A number of extreme storms, critical for a few chosen regions were selected based on H_s time series. For those events, a number of parameters were examined: the overall evolution of atmospheric pressure and wind velocity fields, wind direction resulting in the highest values of H_s and differences in spatial distribution of H_s. Careful examination of storm depressions’ tracks as well as location of the pressure centre during the peak of the storm was conducted. The Empirical Orthogonal Functions (EOF) method was applied to the wind velocity vector fields and pressure fields to enrich our understanding of long-term storm characteristics of these meteorological parameters.

This analysis confirmed our preliminary research results and 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.

References

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

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