Abstract
The effects of the aspect ratios and initial conditions on a cooling mantle with phase changes are studied using a 2-D Cartesian convection model without internal heating. The aspect ratio is either 3 or 5 and the side-boundaries are periodic. The initial condition is either a quasi-equilibrium state of convective flow or linear temperature increase from the top to the bottom surface. Bottom or core temperature is changed to match the core cooling by the convective heat transfer. Considerable qualitative and quantitative differences exist among the models with different initial conditions and aspect ratios. For example, we cannot find the convenient criterion, such as critical Rayleigh number, for the massive overturn of the upper and lower mantle associated with the endothermic phase transition (flushing). The presence of the thermal boundary layer at the endothermic phase boundary plays an important role in cooling both the upper and lower mantles. A common feature is that the upper mantle becomes hottest during the flushing event. In some cases, we find qualitatively similar "events" in which the style of flow changes. These events reflect the physical properties of the upper and lower mantles. Geological information of the past may be necessary to constrain the different models.
