2024年9月27日， 周五15:30-17:00

紫金港西区海纳苑8幢324

Rotating convective motions in rapidly rotating planetary fluid: conduction state, thermal instability, and transition to turbulence

孔大力 (上海天文台)

Abstract：

The problem of thermal convection in rapidly rotating, self-gravitating fluid bodies has been widely modeled in spheres or spherical shells, which implicitly neglects the flattening effect due to the centrifugal force. However, the fast rotation of gaseous giant planets and some of Be stars makes them bulge out enough that they can’t be treated as spheres. As a result, investigating the thermal instability and turbulent convection in oblate spheroids will help better understand the convection processes in these planets and stars or even very flattened systems. In recent works, we first derived a nonspherical reference state model in oblate spheroidal geometry whose shape should be determined by the theory of figure (ToF). A closed-form solution was obtained for gravity and temperature (Kong 2022). Based on this nonspherical conduction state model, the thermal instability problem is formulated in both inertial and viscous convection regimes (Li & Kong 2022; Li & Kong 2023; Li & Kong 2024). The critical properties of inertial modes are explicitly derived. The dependence of the onset of thermal inertial convection on the oblateness of the spheroid is systematically explored. A significant discovery is that the globally most unstable mode could switch from a non-axisymmetric quasi-geostrophic wave to an equatorially symmetric zonal oscillation when the rotational flattening effect gets very strong. This was the only form of global convection not found so far. Stronger nonlinear turbulent dynamics are also explored, and new results imply a new understanding of the formation of mean zonal flow patterns observed on the surfaces of Jupiter and Saturn (Kong & Yuan 2024).

· Works mainly in planetary fluid dynamics and is particularly skilled at analyzing the dynamics of rapidly rotating systems.

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