Upstream surface roughness and terrain are strong drivers of contrast in tornado potential between North and South America

• 成果类型: Article
• 署名作者: Li, Funing; Chavas, Daniel R.; Medeiros, Brian; Reed, Kevin A.; Rasmussen, Kristen L.
• 署名单位: Purdue University System; Purdue University; National Center Atmospheric Research (NCAR) - USA; State University of New York (SUNY) System; Stony Brook University; Colorado State University System; Colorado State University Fort Collins
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8612
• DOI: 10.1073/pnas.2315425121
• 发表日期: 2024-06-25
• 关键词: low-level jet; severe thunderstorm environments; storm-relative helicity; mixed-layer inversion; central united-states; great-plains; synoptic climatology; moisture budget; supercell; MODEL

摘要

Central North America is the global hotspot for tornadoes, fueled by elevated terrain of the Rockies to the west and a source of warm, moist air from equatorward oceans. This conventional wisdom argues that central South America, with the Andes to the west and Amazon basin to the north, should have a tornado alley at least as active as central North America. Central South America has frequent severe thunderstorms yet relatively few tornadoes. Here, we show that conventional wisdom is missing an important ingredient specific to tornadoes: a smooth, flat ocean - like upstream surface. Using global climate model experiments, we show that central South American tornado potential substantially increases if its equatorward land surface is smoothed and flattened to be ocean - like. Similarly, we show that central North American tornado potential substantially decreases if its equatorward ocean surface is roughened to values comparable to forested land. A rough upstream surface suppresses the formation of tornadic environments principally by weakening the poleward low - level winds, characterized by a weakened low - level jet east of the mountain range. Results are shown to be robust for any midlatitude landmass using idealized experiments with a simplified continent and mountain range. Our findings indicate that large - scale upstream surface roughness is likely a first - order driver of the strong contrast in tornado potential between North and South America.