The Importance of Greenland in Setting the Northern Preferred Position of the North Atlantic Eddy-Driven Jet

The North Atlantic atmospheric eddy-driven jet exhibits three “preferred positions,” latitudes where the maximum jet speed occurs more frequently than others. Using an atmospheric general circulation model, Whole Atmospheric Community Climate Model, we explore the extent to which different mountain ranges affect the northern preferred position. The latitude of this preferred position changes only when the latitude of Greenland is changed, and the preferred position disappears when Greenland orography is flattened.We propose that “Greenland tip jet events” create the appearance of a northern “preferred position” in the eddy-driven jet; tip jets are localized zonal jets east of the southern tip of Greenland, created by flow interacting with Greenland orography. In reanalysis data the northern preferred position is strongly associated with tip jet days. A case study with the CAM4 model suggests that biases in the northern preferred position may stem from biases in the position or strength of the climatological eddy-driven jet.