Choosing a formulation

After discussing different reasonable approximations for modeling compressible or incompressible mantle convection, we will now describe the different steps one has to take to use one of these approximations in a computation. As noted towards the beginning of Approximate equations, one should choose a formulation that is adequate for the situation one wants to simulate, taking into account that other authors in previous studies may have used formulations not because they were suited to the situation but also because, possibly, they did not have software available that implemented the most suitable formulation.

The choices involved in selecting a formulation include:

1. Choosing an approximation for the mass conservation equation;

2. Choosing an approximation for the density in the energy balance, and deciding which heating terms should be included;

3. Formulating the buoyancy term in the material model to be used on the right-hand side of the momentum equation;

4. Prescribing a suitable reference state for the temperature, pressure, and density; i.e. the adiabatic profile, if necessary for the approximations chosen in the first three steps.

All of these choices can be made in the input file by selecting the corresponding parameters (see Formulation and Adiabatic conditions model). A description of how to run ASPECT and the basic structure of the input file can be found in Running ASPECT.

• Mass conservation approximation
• Temperature equation approximation
• Approximation of the buoyancy term
• Reference state: The adiabatic profile
• Combined formulations