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arXiv · 2310.12855

Convective scale and subadiabatic layers in simulations of rotating compressible convection

Petri J. Käpylä
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Abstract

(abridged) Context: Rotation is thought to influence the size of convective eddies and the efficiency of convective energy transport in the deep convection zones of stars. Rotationally constrained convection has been invoked to explain the lack of large-scale power in observations of solar flows. Aims: The main aims are to quantify the effects of rotation on the scale of convective eddies and velocity, the depths of convective overshoot, and the subadiabatic Deardorff layers. Methods: Three-dimensional hydrodynamic simulations of rotating convection in Cartesian domains were run. The results were compared with theoretical scaling results that assume a balance between Coriolis, inertial, and buoyancy (Archemedean) forces (CIA balance). Results: The scale of convective eddies decreases as rotation increases, and ultimately reaches a rotationally constrained regime consistent with the CIA balance. Using a new measure of the rotational influence on the system, it is shown that even the deep parts of the solar convection zone are not in the rotationally constrained regime. The simulations capture the slowly and rapidly rotating scaling laws predicted by theory, and the Sun appears to be in between these two regimes. Both, the overshooting depth and the extent of the Deardorff layer, decrease as rotation becomes more rapid. For sufficiently rapid rotation the Deardorff layer is absent. Conclusions: Relating the simulations with the Sun suggests that the convective scale even in the deep parts of the Sun is only mildly affected by rotation and that some other mechanism is needed to explain the lack of strong large-scale flows in the Sun. Taking the current results at face value, the overshoot and Deardorff layers are estimated to span roughly five per cent of the pressure scale height at the base of the convection zone in the Sun.

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Petri J. Käpylä. 2023-10-19. Convective scale and subadiabatic layers in simulations of rotating compressible convection. https://arxiv.org/abs/2310.12855

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