日時 ： ２０１０年２月２６日（金）※16：30～
場所 ： 愛媛大学総合研究棟Ⅰ 4F 共通会議室（理学部構内）
要 旨
A linear stability analysis is performed in order to study the onset of thermal convection in the presence of a strong viscosity variation. We consider the temporal evolution (growth or decay) of an infinitesimal perturbation superimposed to a Boussinesq fluid with an infinite Prandtl number which is in a static (motionless) and conductive state in a basally-heated planar layer or spherical shell. The viscosity of fluid is assumed to be exponentially dependent on temperature. The linearized equations for conservations of mass, momentum and internal (thermal) energy are numerically solved for the critical Rayleigh number as well as the radial profiles of eigenfunctions for infinitesimal perturbations. The above calculations are repeatedly carried out by systematically varying (i) the magnitude of temperature-dependence of viscosity, and (ii) the ratio of inner and outer radii of the spherical shell. A careful analysis of the vertical structure of incipient flows demonstrated that the transition into a stagnant-lid (ST) convection can be marked by the vertical profile of the conversion between horizontal and vertical flows, regardless of the model geometries. We also found that, in the spherical shell relevant to the Earth's mantle, the onset of ST convection takes place at the viscosity contrast across the layer of around 1e4. Taken together with the fact that the above threshold value falls in the range for a so-called sluggish-lid convection, our finding suggests that the ST-mode of convection with elongated convection cells is likely to occur in the Earth's mantle simply from the temperature-dependence of viscosity.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
