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Tug of war on low-level winds and precipitation between elevated terrain and surface roughness over North and South America

Presentation Date
Friday, December 15, 2023 at 2:10pm - Friday, December 15, 2023 at 6:30pm
MC - Poster Hall A-C - South



Low-level atmospheric circulation over central North and South America is characterized by climatological poleward winds, which modulate continental-scale precipitation by carrying warm and moist air from the tropics into the continental interior. It is recognized that these low-level winds intensify with the surface uplift. The Rockies is lower than the Andes by half, yet low-level winds over central North America are at least as strong as that over central South America. Here we show that surface roughness poses a comparable but opposing influence on the low-level winds as compared to surface uplift. We conduct global climate model experiments over North America to show that 1) if the Rockies are as tall as the Andes, the Great Plains low-level winds strongly intensify and hence more precipitation, while the influence of mountains' shape (width and slope) is minor; 2) such an enhancement due to surface uplift is largely canceled out if central North America and the Gulf of Mexico surface is as rough as forested land. Taller mountains intensify winds by strengthening lee cyclogenesis, whereas rougher surface weakens winds by increasing surface friction that deepens the boundary layer. These results emphasize the role of large-scale surface roughness competed with highly elevated terrain in modulating continental low-level circulation and precipitation, which provides insights into understanding the paleo-evolution of extreme weather and climate over North and South America (e.g., the onset of convective precipitation over the central Andes associated with the Andes uplift and the emergence of the Amazon basin during the late Neogene).

Funding Program Area(s)