Competing Geographic Controls on Low‐Level Jets and Regional Precipitation in North and South America

Abstract Low‐level atmospheric circulation over central North and South America, characterized by climatological poleward flow and strong low‐level jets (LLJs), is crucial for regional hydroclimate. These winds are known to intensify with elevated terrain. However, Great Plains LLJs are at least as strong as South American LLJs, despite the Rockies being only half the Andes' height. We hypothesize that the rough forested surfaces east of the Andes compared with the smooth ocean and grassland surfaces east of the Rockies provide an overlooked geographic control on LLJs that compensates for terrain elevation differences. We conduct global climate model experiments to show that higher terrain intensifies LLJs and precipitation, while increased surface roughness largely offsets these effects. Meanwhile, both higher terrain and rougher surfaces raise LLJ height, which helps explain the higher‐altitude LLJs in South America than in North America. These results provide insights into LLJ formation and its variations across regions.