2009, Soomere et al. 2011) and from measurements near Letipea and the SMB model (Suursaar 2010) are discussed above. The long-term average significant wave height estimated using the WAM model (Soomere et al. 2010) is quite small, normally 0.6–0.65 m in the entire Gulf of Finland (Figure 9). The only exception is the entrance area to the gulf and in the central part of this basin, where the average wave height reaches about 0.7 m. The wave height occurring with a probability of 1% is about 2.5 m in the entire open part of the gulf, from the entrance to the Neva Bay. C59 wnt The seasonal variation in the wave activity is clearly evident in both observed and numerically

simulated wave data on the south-eastern coast of the Gulf of Finland. The largest observed waves occur within a four-month period from October to January. The same is largely true for the modelled wave heights, which have a more clearly pronounced maximum find more in December–January. The seasonal courses of modelled waves and wind speeds match each other well, but the observed wave heights show more irregular behaviour, with a secondary maximum in June, and

April being the calmest month. This secondary maximum does not appear for wave fields in the Baltic Proper. There is a secondary maximum in wave intensity in October (which is the overall maximum at Narva-Jõesuu). This feature is not evident in the Baltic Proper either (Räämet & Soomere

2010) and can thus be attributed to the wave climate of the southern Gulf of Finland. The wave model and forcing in use do not reproduce this maximum in the wave activity, which is apparently caused by ageostrophic wind properties. A potential reason is that at times the wind field in the Gulf of Finland contains quite Fossariinae strong easterly and westerly winds blowing along the axis of the gulf (Soomere & Keevallik 2003). This wind system is specific to the Gulf of Finland and does not become evident in other parts of the Baltic Sea; it is much weaker in the eastern part of the gulf. In contrast to the wave directions, wave heights in the Gulf of Finland generally reveal much smaller interannual and decadal variations than those in the Baltic Proper (Kelpšaitė et al. 2009, Soomere et al. 2011). In particular, numerical simulations using one-point wind data suggest that the changes to wave conditions in Tallinn Bay area have been much smaller than those reported for the Baltic Proper (Kelpšaitė et al. 2009). This is not unexpected because the fetch length is relatively short here and the resulting changes to the wave height, especially in the relatively sheltered southern part, should follow the changes in the wind speed, which have been negligible since 1980 (Soomere et al. 2010).