Low-level updraft intensification in response to environmental wind profiles

Supercell storms can develop a “dynamical response” whereby upward accelerations in the lower troposphere amplify as a result of rotationally induced pressure falls aloft. These upward accelerations likely modulate a supercell’s ability to stretch near-surface vertical vorticity to achieve tornadogenesis. This study quantifies such a dynamical response as a function of environmental wind profiles commonly found near supercells. Self-organizing maps (SOMs) were used to identify recurring low-level wind profile patterns from 20,194 model-analyzed, near-supercell soundings. The SOM nodes with larger 0–500 m storm-relative helicity (SRH) and streamwise vorticity (ωs) corresponded to higher observed tornado probabilities. The distilled wind profiles from the SOMs were used to initialize idealized numerical simulations of updrafts. In environments with large 0–500 m SRH and large ωs, a rotationally induced pressure deficit, increased dynamic lifting, and a strengthened updraft resulted. The r...超级单体风暴（supercell storms）可形成“动力响应”机制：对流层（troposphere）低层的向上加速度会因高空旋转诱导的气压降低而增强。此类向上加速度或可调控超级单体拉伸近地面垂直涡度以实现龙卷生成（tornadogenesis）的能力。本研究将此类动力响应表征为超级单体附近常见环境风廓线的函数。研究采用自组织映射（Self-organizing maps, SOMs），从20194份经模式分析的近超级单体探空资料中识别出重复出现的低层风廓线型态。风暴相对螺旋度（storm-relative helicity, SRH）0~500米区间与顺流涡度（streamwise vorticity, ωs）数值更大的自组织映射节点，对应更高的观测龙卷发生概率。从自组织映射中提炼得到的典型风廓线被用于初始化上升气流的理想化数值模拟。在0~500米风暴相对螺旋度与顺流涡度均较大的环境中，会出现旋转诱导的气压亏损、增强的动力抬升与增强的上升气流。The r...