Flow in the lee of idealized mountains and Greenland

Abstract

A series of idealized simulations of flow impinging on large mountains is conducted to investigate the impact of the mountain on the flow far downstream and to shed some light on the effects that Greenland may have on airflow over the North Atlantic. The upstream profiles of wind and stability are kept constant, there is no surface friction, the Rossby number is 0.4, and the nondimensional mountain height (ĥ = Nh/U) is varied from 1 to 6. The maximum sea level pressure deficit, the maximum geopotential height deficit, and the orographically generated potential vorticity all increase with increased ĥ, showing no signs of abrupt change as the flow enters the regime of upstream blocking. The potential vorticity produced at the mountain is accumulated in vortices that are advected downstream. The vortices are associated with a larger pressure gradient to the south of the wake, giving rise to stronger westerlies at the surface as well as at upper levels. This process can explain how Greenland may affect cyclones moving far outside the mountain wake. An example from Fronts and Atlantic Storm Track Experiment (FASTEX) shows that a cyclone moving from the southwest toward Scotland becomes shallower and slower if the Greenland topography is removed.