Lower mantle dynamics with the post-perovskite phase change, radiative thermal conductivity, temperature- and depth-dependent viscosity

The new post-perovskite phase near the core-mantle boundary has important ramifications on lower mantle dynamics. We have investigated the dynamical impact arising from the interaction of temperature- and depth-dependent viscosity with radiative thermal conductivity, up to a lateral viscosity contrast of 10⁴, on both the ascending and descending flows in the presence of both the endothermic phase change at 670 km depth and an exothermic post-perovskite transition at 2650 km depth. The phase boundaries are approximated as localized zones. We have employed a two-dimensional Cartesian model, using a box with an aspect-ratio of 10, within the framework of the extended Boussinesq approximation. Our results for temperature- and depth-dependent viscosity corroborate the previous results for depth-dependent viscosity in that a sufficiently strong radiative thermal conductivity plays an important role for sustaining superplumes in the lower mantle, once the post-perovskite phase change is brought into play. This aspect is especially emphasized, when the radiative thermal conductivity is restricted only to the post-perovskite phase. These results revealed a greater degree of asymmetry is produced in the vertical flow structures of the mantle by the phase transitions. Mass and heat transfer between the upper and lower mantle will deviate substantially from the traditional whole-mantle convection model. Streamlines revealed that an overall complete communication between the top and lower mantle is difficult to be achieved.     

地下水溶质运移数值模拟弥散问题再探

将水动力弥散方程用有限差分法进行离散后编程,通过一具体实例验证其正确性,使之模拟在对流项占优情况下的示踪剂浓度分布,然后针对出现的数值过量、波动和弥散现象介绍国内外一直以来常用的改善或消除方法,提出新的改善方案-从数值随时间步长变化的特点入手,并通过同样的实例验证其可行性,最后就这一方案的优缺点作进一步分析.     

球面正压大气的不稳定与南亚夏季风爆发动力机制的探讨

通过球坐标正压原始方程谱点的计算,发现南亚夏季风爆发前有正压不稳定发生,不稳定罗斯贝波其最大增幅位于南半球的西风急流处,可向低纬传播并能在低纬激发出旺盛的积云对流,该积云对流可造成已失稳的大气基本场发生重大调整,从而导致南亚夏季风的爆发.     

Anisotropy and Dissipation of Turbulence and Their Effects on Solar Models

1 INTRODUCTIONThe maing-length theory (MLT) is the most commonly used approach to calculate convective energy transport in stars and other astrophysical situations. Based on the original idea ofPrandtl (1952) that turbulent parcels trallsfer heat in a similar way as molecules of gas do inthermal conduction, the MLT assumes that convection cells, drived by buoyancy, move thlougha ~ng length 1 and release the heat they carry when they merge with their environment. Themost widely adopted f…     

Radar studies of magnetosphere dynamics

Ionospheric radars are an important tool for studying magnetospheric dynamics. The nature of such instruments is described and their application to a number of important problems is discussed, emphasizing South African work. A study of the theory of reflection from irregularities is discussed. The nature of ULF pulsations of more than one type has been elucidated by radar studies. An improvement of the understanding of magnetospheric convection has been achieved. A new HF radar experiment being developed for operation at SANAE, Antarctica, is described. An HF radar will be operated at SANAE in conjunction with the British radar at Halley to provide vector information about magnetospheric convection within that part of the magnetosphere which maps to a large portion of the Antarctic continent. The radar will be part of the SuperDARN international network of radars.