Numerical Simulation of Tornado-like Vortices Induced by Small-Scale
Cyclostrophic Wind Perturbations
Abstract
This study introduces a tornado perturbation model utilizing the
cyclostrophic wind model, implemented through a shallow-water equation
framework. We conducted numerical simulations to examine development of
perturbations within a static atmosphere background. Four numerical
experiments were conducted: a single cyclonic wind perturbation (EXP1),
a single low-geopotential height perturbation (EXP2), a cyclonic wind
perturbation with a 0 Coriolis parameter (EXP3), and a single
anticyclonic wind perturbation (EXP4). The outputs of these experiments
were analyzed using comparative methods. In a static atmosphere setting,
EXP1 generated a tornado-like pressure structure under a small-scale
cyclonic wind perturbation. The centrifugal force in the central area
exceeded the pressure gradient force, causing air particles to flow
outward, leading to a pressure drop and strong pressure gradient. EXP2
induced a purely radial wind field; upon initiation, the central area
exhibited convergence, and the geopotential height increased rapidly,
indicating that a small-scale depression is insufficient to generate a
tornado’s vortex flow field. EXP3’s results, with a 0 Coriolis
parameter, are marginally different from EXP1, suggesting the Coriolis
force’s negligible impact on small-scale movements. EXP4 demonstrates
that a small-scale anticyclonic wind field perturbation can also trigger
tornado-like phenomena akin to EXP1. The results indicate that a robust
cyclonic and an anticyclonic wind field can potentially generate a pair
of cyclonic and anticyclonic tornadoes, when the horizontal vortex tubes
in an atmosphere with strong vertical wind shear tilt, forming a pair of
positive and negative vorticities. These tornadoes are similar but have
different rotation directions.