American Geophysical Union, Geophysical Research Letters, 17(41), p. 6078-6083
DOI: 10.1002/2014gl061434
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We present an experimental study on the shear instability driven by tidal forcing in a model planetary liquid core. The experimental set-up consists of a water-filled deformable sphere rotating around its axis and subjected to an elliptical forcing. At resonant forcing frequencies, the nonlinear self-interaction of the excited inertial mode drives an intense and localized axisymmetric jet. The jet becomes unstable at low Ekman number because of a shear instability. Using particle image velocimetry measurements, we derive a semi-empirical scaling law that captures the instability threshold of the shear instability. This mechanism is fully relevant to planetary systems, where it constitutes a new route to generate turbulence in their liquid cores.