  We have investigated matter enhanced neutrino oscillations with a
mantle-core-mantle step function and a realistic Earth matter density profile
in both a two and a three neutrino scenario. We found that the realistic Earth
matter density profile can be well approximated with the mantle-core-mantle
step function and that there could be an influence on the oscillation channel
$\nu_\mu \to \nu_\tau$ due to resonant enhancement of one of the mixing angles.
