NUMERICAL INVESTIGATION OF 2D CONVECTION WITH EXTREMELY LARGE VISCOSITY VARIATIONS

Previous experimental studies of convection in fluids with temperature -dependent viscosity reached viscosity contrasts of the order of 10(5) . Although this value seems large, it still might not be large enough for understanding convection in the interiors of Earth and other plane ts whose viscosity is a much stronger function of temperature. The rea son is that, according to theory, above 10(4)-10(5) viscosity contrast s, convection must undergo a major transition-to stagnant lid convecti on. This is an asymptotic regime in which a stagnant lid is formed on the top of the layer and convection is driven by the intrinsic, theolo gical, temperature scale, rather than by the entire temperature drop i n the layer. A finite element multigrid scheme appropriate for large v iscosity variations is employed and convection with up to 10(14) visco sity contrasts has been systematically investigated in a 2D square cel l with free-slip boundaries. We reached the asymptotic regime in the l imit of large viscosity contrasts and obtained scaling relations which are found to be in goad agreement with theoretical predictions. (C) 1 995 American Institute of Physics.