Effect of compressibility on the generation of hydrodynamic helicity in the Earth's liquid core

By the example of a standard three-dimensional model of thermal convection in a rotating spherical shell, it is shown how radial density gradient a-(rho) affects the generation of hydrodynamic helicity chi. For example, the generation of chi weakly depends on a-(rho) inside a Taylor cylinder and, outside the cylinder, the compressibility of the liquid amplifies the generation of chi. The consequences for the geodynamo theory are considered.