Intraseasonal interaction between the Madden–Julian Oscillation and the North Atlantic Oscillation

The North Atlantic Oscillation (NAO), a major source of weather to climate variability over Europe, is generally seen as an intrinsic mode of the atmosphere with no real predictability on medium-range to seasonal timescales. Christophe Cassou now presents evidence that the main climate intra-seasonal oscillation in the tropics (the Madden-Julian Oscillation) controls part of the distribution and sequences of the NAO, and to a lesser extent the other three daily weather regimes that prevail in the region in winter. This finding allows for medium-range predictability of the phase of the NAO far in excess of the one week or so usually quoted as a limit. Cassou presents a simple statistical model to quantitatively assess the potential predictability of the daily NAO index or the sign of its regimes when they occur. His forecasts are successful in about 70% of the cases based on knowledge of the previous 12-day Madden-Julian Oscillation phase as predictor.