Is the North Atlantic Oscillation a Random Walk ?

The North Atlantic Oscillation is a major mode of large-scale climate variability which contains a broad spectrum of variations. There are substantial contributions from short term 2-5 year variations, which have clearly marked teleconnections. Decadal trends are also apparent in the historical historical record of the North Atlantic Oscillation and may be due to either stochas-tic or deterministic processes. Evidence is presented that suggests the NAO exhibits \long-range" dependence having winter values residually correlated over many years. Several simple stochastic models have been used to t the NAO SLP wintertime index over the period 1864-1998, and their performance at predicting the following year has been assessed. Long-range fractionally integrated noise provides a better t than does either stationary red noise or a non-stationary random walk.