The relationships of the North Atlantic Oscillation to water temperature along the southern Baltic Sea Coast

The present paper focuses on the relationships between the North Atlantic oscillation (NAO) index and surface water temperature along the southern Baltic Sea coast. Monthly water temperature values from the period of 1951-2000 were measured in Swinoujscie, Miedzyzdroje, Kolobrzeg, Mielno, Ustka, Wladyslawowo, Hel and Gdynia: sites which are located along the Polish coast. Correlation and regression methods were applied to calculate and analyse the relationships between the NAO index and water temperature. A statistically significant positive correlation between NAO index and the water temperature occurred in winter from December to March with the strongest relationships observed in January followed by February and March. The relationships between the NAO index and water temperature are usually statistically insignificant in the remaining part of the year (April-November). Various kinds of relationships were tested in this study. Our research revealed that asynchronous relationships are rather weak, although in winter they are also statistically significant. They are strongest for the January value of the NAG index combined with February water temperature. However, after three to four months they become statistically insignificant. They regain statistical significance only in late Autumn. It has also been shown that during the cold season, local factors, especially solar ones, weaken the NAO index relationships with the water temperature. This is clearly visible especially towards the turn of winter when insolation increases. During very mild winters the influence of the local factors may be significant beginning from midwinter. Copyright (C) 2007 Royal Meteorological Society.