Therefore, since the beginning of

the visual wave observations, wave heights have behaved similarly at all Estonian coastal observation sites over about thirty years. This coherence and in-phase manner of interannual variations (which can be tracked down to the Lithuanian coast and up to the Swedish coast of the northern CDK inhibitor Baltic Proper) suggest that the interannual changes to wave fields were caused by certain large-scale phenomena embracing the entire Baltic Proper and the Gulf of Finland, that is, with a typical spatial scale >500 km. Surprisingly, this coherence is completely lost in the mid-1980s (Soomere et al. 2011), but subsequently, both wave height trends and details of interannual variations in the wave intensity are different at Vilsandi and at Narva-Jõesuu (Figure 5). Moreover, in contrast to the period before the 1980s, years with relatively high wave intensity at Vilsandi correspond to relatively calm years in Narva Bay and vice versa. The similarity of short-term interannual variations, however, can still be tracked in the northern Baltic Proper selleck screening library until the end of the wave data series at Almagrundet (2003) and to a limited extent to the south-eastern sector of the Baltic

Sea until 2008 (Kelpšaitė et al. 2011, Soomere et al. 2011). The short-term interannual variations in the temporal course of the annual mean wave heights calculated from climatologically corrected data sets of visual observations are almost identical to those in Figure 5 (Soomere et al. 2011). The climatological correction of observed wave data leads to a substantial increase

in the correlation between simulated and observed annual mean wave heights, Loperamide in particular, for years of coherent observed and simulated interannual changes (Soomere et al. 2011). This feature is not unexpected, because introducing such a correction is equivalent to largely ignoring the ice cover. Decadal and long-term variations. Both observed and measured wave data reveal substantial variations in the annual mean wave height in the northern Baltic Proper. There is an increase in the mean wave height at Vilsandi and for a few years at Pakri around the year 1960 and an overall slow decrease until the mid-1970s. The most significant feature in the long-term behaviour of the Baltic Sea wave fields is the rapid increase in the annual mean wave height in the northern Baltic Proper from the mid-1980s until the mid-1990s. The increase was well over 1% per annum depending on the particular choice of the time interval and the site (Almagrundet 1979–92: 1.3%; 1979–95: 1.8% (Broman et al. 2006); Vilsandi 1979–95 as high as 2.8% (Soomere & Zaitseva 2007)). This trend follows the analogous trends for the southern Baltic Sea and for the North Atlantic (Gulev & Hasse 1999, Weisse & Günther 2007).