Effects of large-scale atmospheric circulation on the Baltic Sea wave climate: application of EOF method on multi-mission satellite altimetry data

Wave heights in the Baltic Sea in the period 1992–2015 have mainly increased in the sea’s western parts. The linear trends in the winter wave heights exhibit a prominent meridional pattern. Using the technique of Empirical Orthogonal Functions (EOF) applied to multi-mission satellite altimetry data, we explain a large part of this increase with the Scandinavia pattern, North Atlantic Oscillation and Arctic Oscillation climatic indices. The winter trends show a statistically significant negative correlation (correlation coefficient –0.47 ± 0.19) with the Scandinavia pattern and a positive correlation with the North Atlantic Oscillation (0.31 ± 0.22) and Arctic Oscillation (0.42 ± 0.20). The meridional pattern is associated with more dominant north-westerly and westerly winds driven by the Scandinavia pattern and North Atlantic Oscillation, respectively. All three climatic indices show a statistically significant time-variable correlation with Baltic Sea wave heights during the winter season. When the Scandinavia pattern’s influence is strong, the North Atlantic and Arctic Oscillation effects are low and vice versa. The results are backed up by simulations using synthetic data that demonstrate that the percentage of variance explained using EOF analysis from the satellite-derived wave measurements is directly related to the percentage of noise in the data and that the retrieved spatial patterns are insensitive to the level of noise.