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Abstract Although much is known about the environmental conditions necessary for supercell tornadogenesis, the near-ground vorticity dynamics during the tornadogenesis process itself are still somewhat poorly understood. For instance, seemingly contradicting mechanisms responsible for large near-ground vertical vorticity can be found in the literature. Broadly, these mechanisms can be sorted into two classes, one being based on upward tilting of mainly baroclinically produced horizontal vorticity in descending air (here called the downdraft mechanism), while in the other the horizontal vorticity vector is abruptly tilted upward practically at the surface by a strong updraft gradient (referred to as the in-and-up mechanism). In this study, full-physics supercell simulations and highly idealized simulations show that both mechanisms play important roles during tornadogenesis. Pretornadic vertical vorticity maxima are generated via the downdraft mechanism, while the dynamics of a fully developed vortex are dominated by the in-and-up mechanism. Consequently, a transition between the two mechanisms occurs during tornadogenesis. This transition is a result of axisymmetrization of the pretornadic vortex patch and intensification via vertical stretching. These processes facilitate the development of the corner flow, which enables production of vertical vorticity by upward tilting of horizontal vorticity practically at the surface, i.e., the in-and-up mechanism. The transition of mechanisms found here suggests that early stages of tornado formation rely on the downdraft mechanism, which is often limited to a small vertical component of baroclinically generated vorticity. Subsequently, a larger supply of horizontal vorticity (produced baroclinically or via surface drag, or even imported from the environment) may be utilized, which marks a considerable change in the vortex dynamics.
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The Shaker: A Platform for Active Perturbations in Neuromechanical Studies of Small Animals
In this paper, we inform about the development of a three degrees of freedom active platform for neuromechanical experiments. This platform, termed ‘the shaker’, generates single or combined horizontal, vertical, and tilting perturbations with a payload up to 1 kg. It can produce horizontal and vertical perturbations with amplitudes up to 1 cm at oscillation frequencies up to 10 Hz. The tilting motions were constrained to 15°/s. The shaker can measure single ground reaction forces (GRF) using up to four custom-build force plates mounted on the platform. Preliminary experiments with rats combining X-ray fluoroscopy, and three dimensional GRF during active perturbations were performed. They indicate that the shaker may play a key role in determining motor-control strategies in response to active perturbations during posture and locomotion in small animals.
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- Award ID(s):
- 2015317
- PAR ID:
- 10424823
- Date Published:
- Journal Name:
- Biomimetic and Biohybrid Systems
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1007/978-3-031-20470-8_10
