Circulation Around a Constrained Curve: An Alternative Analysis Tool for Diagnosing the Origins of Tornado Rotation in Numerical Supercell Simulations
Circulation Around a Constrained Curve: An Alternative Analysis Tool for Diagnosing the Origins of Tornado Rotation in Numerical Supercell Simulations
复制标题
围绕约束曲线的循环：用于诊断数值超胞模拟中龙卷风旋转起源的替代分析工具
DOI：
10.1175/jas-d-21-0020.1
复制
发表时间：
2021
影响因子：
3.1
通讯作者：
MARKOWSKI, PAUL M.
中科院分区：
文献类型：
--
作者：
DAVIES-JONES, ROBERT;MARKOWSKI, PAUL M.
超级单体风暴的高分辨率计算机模型生成了逼真的龙卷风漩涡。就像真实的龙卷风一样，这些虚拟漩涡的起源是神秘的。为了诊断龙卷风的起源，通常会在龙卷风周围画出一个近地面物质回路，然后利用反向轨迹来追踪这个回路。绕回路环流的变化率等于总环流力。这个环流定理被用来推导龙卷风大涡度的起源。然而，这种方法存在一个众所周知的问题;对于交错网格，包裹轨迹变得不确定，因为它们陷入了靠近地面的层中，在那里水平风无法插值。为了避免这种困境，我们得到了一个广义循环定理，适用于任何电路。我们将这个定理应用于被约束到简单曲面的移动电路，或者应用于下面定义的“混合”电路。使水平面与地面保持一个网格间距. A回路作为材料回路移动。随着水平风向A方向移动的水平曲线段取代了低于A方向的材料回路段。修改电路的循环方程包括保持曲线段水平所需的惯性力的力循环。这一项很容易在A上求值。使用平面或圆形电路有助于解释一些简单的流程。混合电路的方法显着提高了在一个理想化的超级单体模拟环流预算的准确性。
Fine-resolution computer models of supercell storms generate realistic tornadic vortices. Like real tornadoes, the origins of these virtual vortices are mysterious. To diagnose the origin of a tornado, typically a near-ground material circuit is drawn around it. This circuit is then traced back in time using backward trajectories. The rate of change of the circulation around the circuit is equal to the total force circulation. This circulation theorem is used to deduce the origins of the tornado’s large vorticity. However, there is a well-known problem with this approach; with staggered grids, parcel trajectories become uncertain as they dip into the layer next to the ground where horizontal wind cannot be interpolated. To circumvent this dilemma, we obtain a generalized circulation theorem that pertains to any circuit. We apply this theorem either to moving circuits that are constrained to simple surfaces or to a “hybrid” circuit defined next. LetAbe the horizontal surface at one grid spacing off the ground. AboveAthe circuit moves as a material circuit. Horizontal curve segments that move inAwith the horizontal wind replace segments of the material circuit that dip belowA. The circulation equation for the modified circuit includes the force circulation of the inertial force that is required to keep the curve segments horizontal. This term is easily evaluated onA. Use of planar or circular circuits facilitates explanation of some simple flows. The hybrid-circuit method significantly improves the accuracy of the circulation budget in an idealized supercell simulation.