Shanghai Astronomical Observatory Astrophysics Colloquium

Title：The onset of thermal instabilities in rapidly rotating self-gravitating oblate spheroidal fluid

Speaker：Dr. Dali Kong (SHAO)

Location: Lecture Hall, 3rd floor

Time：3:00 pm Feb. 16th (Thursday)

Abstract：

Motivated by its applications in planetary and stellar physics, the problem of convective instability 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. In this presentation, by self-consistently considering the centrifugal force, rapidly rotating stably stratified Boussinesq fluid is firstly modeled in oblate spheroidal cavities whose geometric shapes are determined by the theory of figure. A closed-form solution is obtained for gravity and temperature. Based on this nonspherical model of the conduction state, the problem of thermal instabilities is formulated in the regime of inertial convection, which is marked by an asymptotically small Ekman number and a sufficiently small Prandtl number. 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.

The fast rotation of planets like Jupiter and Saturn makes them bulge out enough that they can’t be treated as spheres. Investigating the thermal instabilities in oblate spheroids will help researchers better understand the convection processes in these planets and could also lead to insights into very flattened systems like accretion disks around black holes.

CV：

Dr. Dali Kong graduated from the Department of Astronomy, Nanjing University, in 2008 and obtained his Ph.D. in Applied Mathematics from the University of Exeter in 2012. He joined Shanghai Astronomical Observatory in 2017 after spending five years of Postdoc fellowship at the Centre for Geophysical and Astrophysical Fluid Dynamics, University of Exeter. Dr. Kong mainly works in planetary fluid dynamics, particularly skilled at analyzing the dynamics of rapidly rotating systems.