高原地形与墨西哥湾在北美强局地风暴环境生成中的作用
The role of elevated terrain and the Gulf of Mexico in the production of severe local storm environments over North America
AI总结：
本研究通过气候模型实验发现，北美强局地风暴环境强烈依赖上游高原地形，而对墨西哥湾依赖较弱；移除地形显著减少内陆风暴环境，而将墨西哥湾变为陆地则使风暴环境东移并改变其分布。
摘要：
关于北美强局地风暴（SLS）环境生成的流行概念模型认为，上游高原地形和墨西哥湾对其形成均至关重要。本研究通过两个指定海洋的气候模型实验检验了这一假设，实验分别移除北美地形或将墨西哥湾转换为陆地，并分析了SLS环境及相关天气尺度驱动因子（大平原南部低空急流、干线、抬升混合层和温带气旋）相对于对照历史模拟的变化。总体而言，SLS环境强烈依赖于上游高原地形，而对墨西哥湾的依赖较弱。移除高原地形显著减少了SLS环境，尤其是在大陆内部，这是由于热力学和运动学参数均大幅减少，导致残余分布更呈纬向均匀，在墨西哥湾沿岸附近达到最大，并向大陆内部衰减。这一响应与天气尺度驱动因子的显著减少以及平均态大气更冷更干有关。将墨西哥湾替换为陆地则适度减少了大平原地区SLS环境的热力学条件，同时增加了美国东部的运动学条件，使主要局地最大值东移至伊利诺伊州；同时消除了得克萨斯州南部的次要较小局地最大值。这一响应与天气尺度驱动因子的适度变化以及低层大气平均态更暖更干有关。这些实验揭示了高原地形和墨西哥湾在改变SLS环境空间分布和季节性方面的作用。
英文摘要：
The prevailing conceptual model for the production of severe local storm (SLS) environments over North America asserts that upstream elevated terrain and the Gulf of Mexico are both essential to their formation. This work tests this hypothesis using two prescribed-ocean climate model experiments with North American topography removed or the Gulf of Mexico converted to land and analyzes how SLS environments and associated synoptic-scale drivers (southerly Great Plains low-level jets, drylines, elevated mixed layers, and extratropical cyclones) change relative to a control historical run. Overall, SLS environments depend strongly on upstream elevated terrain but weakly on the Gulf of Mexico. Removing elevated terrain substantially reduces SLS environments especially over the continental interior due to broad reductions in both thermodynamic and kinematic parameters, leaving a more zonally-uniform residual distribution that is maximized near the Gulf coast and decays toward the continental interior. This response is associated with a strong reduction in synoptic-scale drivers and a cooler and drier mean-state atmosphere. Replacing the Gulf of Mexico with land modestly reduces SLS environments thermodynamically over the Great Plains and increases them kinematically over the eastern U.S, shifting the primary local maximum eastward into Illinois; it also eliminates the secondary, smaller local maximum over southern Texas. This response is associated with modest changes in synoptic-scale drivers and a warmer and drier lower-tropospheric mean state. These experiments provide insight into the role of elevated terrain and the Gulf of Mexico in modifying the spatial distribution and seasonality of SLS environments.
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