COLLABORATIVE RESEARCH: Numerical studies of double-diffusive convection in the interior of giant planets

不稳定的热梯度和稳定的成分梯度（即双扩散对流）的竞争效应在巨行星的结构和演化中起着重要作用。它们与观测到的天王星的低热通量、天王星和海王星外壳的高金属丰度、木星和土星核心的侵蚀以及一些观测到的凌日系外行星的大半径有关。在全球海洋混合的背景下进行广泛的研究是不适用的，因为这两种情况下的控制参数之间存在很大的差异。这个合作项目将在相关参数范围内对双扩散对流进行最先进的三维高分辨率数值模拟，分析它们以提取实际的通量参数化，并修改现有的行星演化代码（CEPAM）来解释这种影响。这种改进的技术随后将用于解决两个具体问题：(i)修订后的热通量定律如何影响行星的热演化和结构，以及（ii）化学元素如何在其组成界面上混合。这方面的进展对于更好地理解巨大行星的全球演化将是无价的一步。这项工作是地球物理和天体物理流体动力学之间的交叉学科，自然会使这两个学科受益，也会培养研究生。radko博士将出版一本关于双扩散过程的专著，以加强向科学界的传播。

AST-0807672/0806431Garaud/RadkoThe competing effects of destabilizing thermal gradients and stabilizing compositional gradients (i.e. double-diffusive convection) play a major role in the structure and evolution of giant planets. They relate to the low observed heat flux of Uranus, the high metallicity of the envelopes of Uranus and Neptune, the erosion of the cores of Jupiter and Saturn, and the large radii of some observed transiting exoplanets. Extensive studies in the context of global oceanic mixing are not applicable because of the wide discrepancy between the governing parameters in the two cases. This collaborative project will perform state-of-the-art three-dimensional high-resolution numerical simulations of double-diffusive convection in the relevant parameter regime, analyze them to extract practical flux parameterizations, and modify an existing planetary evolution code (CEPAM) to account for the effects. This improved technique will then be used to address two particular questions: (i) How do the revised heat flux laws affect the thermal evolution and structure of the planets, and (ii) How are chemical elements mixed across their compositional interfaces. Progress here would be an invaluable step towards a better understanding of the global evolution of giant planets everywhere.This work is interdisciplinary between geophysical and astrophysical fluid dynamics, and will naturally benefit both subjects, as well as training a graduate student. Dissemination to the scientific community will be enhanced by publication of a monograph on Double-Diffusive Processes by Dr.Radko.