We classified different plume types in terms of their geoid signals. These calculations have been done using a Finite Element convection code in axi-symmetric spherical shell geometry, where the plumes developed at the pole. We ran simulations of sixteen different viscosity distributions for three different Rayleigh numbers. They illustrate scenarios where hot plumes have a larger or smaller influence on the geoid and topography compared to the constant viscosity case. We now are able to define different classes of plumes by classifying their geoid signals.
Class 1). Mainly depth dependent viscosity:
A viscosity which changes essentially with depth has a completely different effect on the shape of the geoid. For strongly depth dependent cases, a geoid with negative sign shows up and for less depth dependent viscosity, a positive sign with small amplitude geoid appears. This can be considered as a transition between strongly depth dependent and constant viscosity case.