On the Drivers of Decadal Variability of the Gulf Stream North Wall

The Gulf Stream is bounded to the north by a strong temperature front known as the North Wall. The North Wall is subject to variability on a wide range of temporal and spatial scales-on interannual time scales, the dominant mode of variability is a longitudinally coherent north-south migration. North Wall variability since 1970 has been characterized by regular oscillations with a period of approximately nine years. This periodic variability, and its relationship to major modes of Atlantic climate variability, is examined in the frequency domain. The North Atlantic Oscillation (NAO) and the Atlantic meridional mode (AMM) both covary with the North Wall on decadal time scales. The NAO leads the North Wall by about one year, whereas the covariability between the North Wall and the AMM is synchronous (no lag). Covariability between the North Wall and the NAO is further examined in terms of the centers of action comprising the NAO: the Icelandic low and Azores high. It is found that the strength of the Icelandic low and its latitude as well as the strength of the Azores high play a role in decadal North Wall variability.