Flows in librating spheres-Resonant and non-resonant flows in longitudinally and latitudinally librating spheres

<p>We investigate the linear response to longitudinal and latitudinal libration of a rapidly rotating fluid-filled sphere. Asymptotic methods are used to explore the structure of resonant modes in both cases, provided that the nondimensional libration frequency is in the range 0<ω<2. High-resolution numerics are then used to map out this entire frequency range, picking out both the resonant peaks as well as the non-resonant troughs in between. The kinetic energy is O(1) at the peaks, and O(E<sup>1/2</sup>) at the troughs. As the Ekman number is reduced, down to E=10<sup>-10</sup> for longitudinal libration and E=10<sup>-9</sup> for latitudinal libration, the frequency response also exhibits an increasingly fractal structure, with more and more peaks and troughs emerging. The spacing between peaks is seen to follow an E<sup>1/2</sup> self-similarity factor. However, detailed examinations of some of the more prominent troughs shows that their widths follow an E<sup>~0.23</sup> self-similarity factor.</p>