Decadal and long-term variations in the wave climate at the Latvian coast of the Baltic Proper

Abstract

We present an estimate of the main parameters of the wave climate at the eastern coast of the Baltic Proper based on recently digitized data of historical visual wave observations from Ventspils, Latvia (57°24'N, 21°32'E) for 1954–2011. The features of the local wave climate (the average wave properties, frequency of occurrence of waves of different heights and periods, joint distribution of wave heights and periods) match the existing knowledge about the wave properties in this area. The long-term average wave height in the nearshore is about 0.6 m and typical wave periods are 2–5 s. The strongest signal in the data is the seasonal course in wave heights. Relatively strong decadal changes and especially interannual variability in the average wave height largely mask long-term trends. The annual mean wave height decreased considerably in the 1950s and the 1960s and gradually increased from 1970 onwards. The formal trends are statistically insignificant. Long-term and decadal variations in the mean significant wave height are compared with similar data from other wave observation sites in the north-eastern and south-eastern parts of the Baltic Sea (Vilsandi and Pakri in Estonia, Nida in Lithuania).