|
E. Linacre |
10/'98 |
There have been changes from one decade to another in the storm and wave climate of the north-east Atlantic, but no overall trend this century (1). A storm index based on estimated geostrophic wind strengths in the waters surrounding Scandinavia shows relatively high values in 1880, 1902, 1923, 1950, and 1990, and intervening minima in 1895, 1910, 1940 and 1964. The decadal changes are partly due to the ‘North Atlantic Oscillation’ (2), and they are statistically significant, i.e. they invalidate conventional estimation of extreme values, which assumes a random distribution.
Waves just west of Ireland, from 50ºN to 55ºN, had an annual mean extreme height of 11.1 metres during 1961-87, and they were higher than 5.8 m during 10% of the period. These heights increased by 0.3 and 0.7 m, respectively, over the period. A computer model of the effect of doubled CO2 indicates waves in the Bay of Biscay higher by up to 0.5 m, but lower waves west of Ireland.
References
(1) WASA 1998. Changing waves and storms in the northeast Atlantic? Bull. Amer. Meteor. Soc., 79, 741-60.
(2) Hurrell, J.W. 1995. Decadal trends in the North Atlantic Oscillation regional temperatures and precipitation. Science 269, 676-9.