Supercell Low-Level Mesocyclones: Origins of Inflow and Vorticity
Supercell Low-Level Mesocyclones: Origins of Inflow and Vorticity
复制标题
超级单体低层中气旋：流入和涡度的起源
DOI：
10.1175/mwr-d-22-0269.1
复制
发表时间：
2023
影响因子：
3.2
通讯作者：
Wade, Andrew R.
中科院分区：
文献类型：
--
作者：
Coffer, Brice E.;Parker, Matthew D.;Peters, John M.;Wade, Andrew R.
超级单体雷暴中低层中气旋的发展和强化通常至少部分归因于超级单体前翼斜压产生的增强流向涡度。然而，环境的环境流向涡度（通常通过风暴相对螺旋度进行量化），特别是在地面附近，特别擅长区分非龙卷风和龙卷风超级单体。这项研究调查了流入超级单体低层中气旋的空气来源（无论是水平还是垂直）是否可以帮助解释环境与风暴产生的涡度在低层中气旋旋转发展中的动力学作用。对超级单体的模拟，以自然界中观察到的超级单体环境中常见的风廓线进行初始化，结果表明，流向低层中气旋的空气主要来自周围环境（而不是沿着前翼），并且来自非常接近地面的地方，通常位于大气层的最低 200-400 m 处。鉴于近地环境空气占低层中气旋流入量的大部分，这可能解释了大气层最低几百米的环境流向涡度的预报技巧。低层中气旋似乎不需要通过在前翼发展额外的水平涡度来增强。相反，低层中气旋内垂直涡度的主要贡献者来自环境水平涡度。这项研究为正在进行的有关超级单体低层中气旋内部旋转发展的讨论提供了进一步的背景。意义陈述超级单体雷暴产生了大部分龙卷风，超级单体的一个决定性特征是它们的旋转上升气流，称为“中气旋”。当中气旋在低海拔地区较强时，发生龙卷风的可能性就会增加。本研究的目的是了解超级单体中中气旋的旋转是否是由于周围环境中存在的水平旋转所致，或者风暴本身产生的额外水平旋转是否主要驱动这种旋转。我们的结果表明，流入超级单体的空气和低层中气旋旋转主要是由于环境流入空气的特性，特别是在地面附近。这有望为我们的社区如何看待超级单体中低级中气旋的发展提供进一步的背景。
The development and intensification of low-level mesocyclones in supercell thunderstorms have often been attributed, at least in part, to augmented streamwise vorticity generated baroclinically in the forward flank of supercells. However, the ambient streamwise vorticity of the environment (often quantified via storm-relative helicity), especially near the ground, is particularly skillful at discriminating between nontornadic and tornadic supercells. This study investigates whether the origins of the inflow air into supercell low-level mesocyclones, both horizontally and vertically, can help explain the dynamical role of environmental versus storm-generated vorticity in the development of low-level mesocyclone rotation. Simulations of supercells, initialized with wind profiles common to supercell environments observed in nature, show that the air bound for the low-level mesocyclone primarily originates from the ambient environment (rather than from along the forward flank) and from very close to the ground, often in the lowest 200–400 m of the atmosphere. Given that the near-ground environmental air comprises the bulk of the inflow into low-level mesocyclones, this likely explains the forecast skill of environmental streamwise vorticity in the lowest few hundred meters of the atmosphere. The low-level mesocyclone does not appear to require much augmentation from the development of additional horizontal vorticity in the forward flank. Instead, the dominant contributor to vertical vorticity within the low-level mesocyclone is from the environmental horizontal vorticity. This study provides further context to the ongoing discussion regarding the development of rotation within supercell low-level mesocyclones.Significance StatementSupercell thunderstorms produce the majority of tornadoes, and a defining characteristic of supercells is their rotating updraft, known as the “mesocyclone.” When the mesocyclone is stronger at lower altitudes, the likelihood of tornadoes increases. The purpose of this study is to understand if the rotation of the mesocyclone in supercells is due to horizontal spin present in the ambient environment or whether additional horizontal spin generated by the storm itself primarily drives this rotation. Our results suggest that inflow air into supercells and low-level mesocyclone rotation are mainly due to the properties of the environmental inflow air, especially near the ground. This hopefully provides further context to how our community views the development of low-level mesocyclones in supercells.