The material presented also highlights a number of questions. A problem that calls for further research is the mismatch between the course of decadal variability learn more in wave heights and the gradual increase in wind speed over the northern Baltic Proper. While the wave activity reveals rapid decadal-scale variations, the annual mean wind speed at the island of Utö shows a gradual

increase over this time (Broman et al. 2006). Progress in the understanding of the reasons behind this mismatch may essentially contribute to our ability to reconstruct the wind properties and other meteorological parameters in the open sea. The reason behind the reported changes to the wave periods and directions as well their potential consequences in terms of coastal and offshore engineering and coastal zone management need to be clarified. Also, it is not fully clear why there

is effectively no correlation between the interannual variability in the wave intensity and the ice conditions on the Estonian coast (Soomere et al. 2011). It is well known that wind fields reconstructed from atmospheric models frequently underestimate open sea wind speeds. It is therefore not unexpected that runs based on high-quality ECMWF wind fields result in a certain find more underestimation of the wave properties. It is, however, remarkable that the highly sophisticated ECMWF model consistently leads to results that differ only insignificantly from those obtained with the use of the simplest adjustment of the geostrophic wind. Therefore, although the

geostrophic wind suffers from shortcomings for semi-enclosed sea areas, its use for long-term wave hindcast properties seems to be a very reasonable, if not the best, way to account for realistic wind fields in the Baltic Sea today. There are, of course, clear limitations to its use. For example, one can trust general statistics and selected trends but generally not hindcast time series or instantaneous values. Therefore, an alternative source of wind information is necessary in order ALOX15 to reproduce the temporal course of wave fields in particular storms. A first-order solution would be, for example, the use of altimeter data and, if possible, scatterometer data. The authors are deeply grateful to Loreta Kelpšaitė for discussions about wave conditions along the Lithuanian coasts, to Inga Zaitseva-Pärnaste and Olga Tribštok for digitizing historical wave observations from the archives of the Estonian Hydrological and Meteorological Institute, and to Ülo Suursaar for providing original simulation data for Figure 6. The ECMWF winds were kindly presented by Luciana Bertotti and Luigi Cavaleri for the reconstruction of wave fields in extreme wave storms in the Baltic Sea basin. “
“The sea level in the Baltic changes considerably throughout the year as a result of the superimposing effects of a number of meteorological and hydrographic factors.