The supernova-regulated ISM. III. Generation of vorticity, helicity and mean flows
| Autor: | Maarit J. Käpylä, Frederick A. Gent, Miikka S. Väisälä, Graeme R. Sarson |
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| Přispěvatelé: | Centre of Excellence Research on Solar Long-Term Variability and Effects, ReSoLVE, Department of Computer Science, Newcastle University, Aalto-yliopisto, Aalto University, Department of Physics |
| Rok vydání: | 2017 |
| Předmět: |
DRIVEN INTERSTELLAR-MEDIUM
Baroclinity Direct numerical simulation FOS: Physical sciences Astrophysics Rotation 01 natural sciences 7. Clean energy MAGNETIC-FIELDS 010305 fluids & plasmas Physics::Fluid Dynamics IONIZED-GAS Vortex stretching 0103 physical sciences DYNAMO 010303 astronomy & astrophysics Physics ISM [galaxies] Turbulence NUMERICAL SIMULATIONS turbulence Astronomy and Astrophysics Mechanics Vorticity 115 Astronomy Space science Helicity Astrophysics - Astrophysics of Galaxies 13. Climate action Space and Planetary Science instabilities Astrophysics of Galaxies (astro-ph.GA) DENSITY POWER SPECTRUM hydrodynamics MILKY-WAY SHEAR-FLOW Shear flow galaxies: ISM ELECTRON-DENSITY |
| DOI: | 10.48550/arxiv.1705.08642 |
| Popis: | The forcing of interstellar turbulence, driven mainly by supernova explosions, is irrotational in nature, but the development of significant amounts of vorticity and helicity, accompanied by large-scale dynamo action, has been reported. Several earlier investigations examined vorticity production in simpler systems; here all the relevant processes can be considered simultaneously. We also investigate the mechanisms for the generation of net helicity and large-scale flow in the system. We use a three-dimensional, stratified, rotating and shearing local simulation domain of the size 1x1x2 kpc$^3$, forced with SN explosions occurring at the rate typical of the solar neighbourhood in the Milky Way. In addition to the nominal simulation run with realistic Milky Way parameters, we vary the rotation and shear rates, but keep the absolute value of their ratio fixed. Reversing the sign of shear vs. rotation allows us to separate the rotation- and shear-generated contributions. As in earlier studies, we find the generation of significant amounts of vorticity, with on average 65% of the kinetic energy being in the rotational modes. The vorticity production can be related to the baroclinicity of the flow, especially in the regions of hot, dilute clustered supernova bubbles. In these regions, the vortex stretching acts as a sink of vorticity. The net helicities produced by rotation and shear are of opposite signs for physically motivated rotation laws, with the solar neighbourhood parameters resulting in the near cancellation of the total net helicity. We also find the excitation of oscillatory mean flows, the strength and oscillation period of which depend on the Coriolis and shear parameters; we interpret these as signatures of the anisotropic kinetic (AKA) effect. We use the method of moments to fit for the turbulent transport coeffcients, and find $\alpha_{\rm AKA}$ values of the order 3-5 km/s. Comment: 19 pages, 12 figures, Astronomy and Astrophysics, accepted for publication |
| Databáze: | OpenAIRE |
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