Scale Interactions over the North Atlantic: Connections between the North Atlantic Oscillation, the El Nino/Southern Oscillation and intraseasonal variations

The climate in the North Atlantic region undergoes variations on a broad range of time scales ranging from one or two years to several decades. These variations are typically assigned to such prominent phenomena as the North Atlantic Oscillaion (NAO) or the El Nino/Southern Oscillation (ENSO). At the short end of the spectrum the atmosphere undergoes variations between time scales of several days, i.e., extratropical cyclones and several weeks, i.e., blocking or cutoff lows. These variations on intraseasonal time scales are, however, not only affected by the interannual climate variations, but feed back on these long-term variations by means of nonlinear interactions. In our study we investigate the connections between the NAO and ENSO on one hand and the interactions between the interannual climate variations and the intraseasonal variations over the North Atlantic on the other. This is done on the basis of a 300-year simulation of the present-day climate with the ECHO-G coupled atmosphere ocean model. This simulation reveals a rich spectrum of variability for both ENSO and the NAO. We concentrate on the boreal winter season, i.e., January, February and March, when we find a strong coupling between the NAO and ENSO as well as the strongest intraseasonal variability over the North Atlantic.