The dependence of convection planform on mode of heating

Abstract

A fundamental property of a convecting fluid is its planform—the distribution in the horizontal plane of hot rising regions and cold sinking regions. For the Earth's mantle the planform might he visualized as a map of subduction zones, hotspots and possibly ocean ridges. Here I report numerical experiments of convection at high Rayleigh number which show a strong dependence of planform on heating mode. When heat generation is distributed uniformly through the box the preferred planform consists of an ensemble of time-dependent cold axial sinkers distributed in a hot diffuse upward flow. When half of the heat is generated within the box and the other half is input through the base, the preferred planform consists of an array of hot axial plumes and elongated cold sheets. In the former case the mean horizontal wavelength is about equal to the layer depth; for the latter it is about twice the layer depth.