The dominant influence of the Icelandic Low on the position of the Gulf Stream northwall

The location where the Gulf Stream separates from the American coast and turns eastward is called its northwall. The interannual fluctuations of the northwall are significantly correlated with the North Atlantic Oscillation with a lag of two years. When the Azores High and the Icelandic Low pressures are taken as independent variables, the latter dominates the relationship with the northwall, and the influence of the Azores High pressure is insignificant. This is consistent with the hypothesis that the major oceanic control of the northwall is in the southward flow of Labrador Sea Water into the Slope Sea. The alternative mechanism that the interaction of westward propagating Rossby waves with the American coast is responsible for northwall fluctuations is considered less likely because its initiation requires perturbations of the eastward winds in the mid-Atlantic region, and they are very likely dependent on the Azores High. The analysis suggests that the time lag between perturbations of the Icelandic Low and the northwall varies between one and three years.