Roles of the Rocky Mountains in the Atlantic and Pacific Meridional Overturning Circulations

Abstract

AbstractThe effect of the Rocky Mountains (RM) on meridional overturning circulations (MOCs) is investigated using a fully coupled climate model. Located between the Atlantic and Pacific oceans, the RM is the major mountains in North America. It presence plays an important role in atmospheric moisture transport between the two oceans. Adding the RM to a flat global continent (OnlyRocky) leads to a weakening of the atmospheric moisture transport from the North Pacific to the North Atlantic, which is consistent with previous finding. However, the simulation also shows more atmospheric moisture is transported from the tropical Pacific and Atlantic to the North Atlantic. The net effect of moisture transport leads to a slight freshening of the North Atlantic. The Atlantic MOC (AMOC) is hardly changed, but the Pacific MOC (PMOC) declines by 40% due to more moisture retained in the North Pacific. The sensitivity experiment of removing the RM from a realistic global topography (NoRocky) gives roughly opposite atmospheric changes to the OnlyRocky experiment. The AMOC in NoRocky declines slightly and then recovers, while the PMOC is nearly unchanged. The paired experiments conducted in this study demonstrate that the presence of the RM plays a trivial role in Northern Hemisphere deep-water formation.