Super-Reflection in Fluid Discs: Corotation Amplifier, Corotation Resonance, Rossby Waves, and Overstable Modes - AstrophysicsReport as inadecuate




Super-Reflection in Fluid Discs: Corotation Amplifier, Corotation Resonance, Rossby Waves, and Overstable Modes - Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: In differentially rotating discs with no self-gravity, density waves cannotpropagate around the corotation, where the wave pattern rotation speed equalsthe fluid rotation rate. Waves incident upon the corotation barrier may besuper-reflected commonly referred to as corotation amplifier, but thereflection can be strongly affected by wave absorptions at the corotationresonance-singularity. The sign of the absorption is related to the Rossby wavezone very near the corotation radius. We derive the explicit expressions forthe complex reflection and transmission coefficients, taking into account waveabsorption at the corotation resonance. We show that for generic discs, thisabsorption plays a much more important role than wave transmission across thecorotation barrier. Depending on the sign of the gradient of the specificvorticity of the disc the corotation resonance can either enhance or diminishthe super-reflectivity, and this can be understood in terms of the location ofthe Rossby wave zone relative to the corotation radius. Our results provide theexplicit conditions in terms of disc thickness, rotation profile and specificvorticity gradient for which super-reflection can be achieved. Globaloverstable disc modes may be possible for discs with super-reflection at thecorotation barrier.



Author: David Tsang, Dong Lai

Source: https://arxiv.org/







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