On the treatment of the Coriolis force in computational astrophysics

In numerical computations of astrophysical flows one frequently has to deal with situations which require the use of a corotating coordinate system. Then, in addition to the centrifugal force, the Coriolis terms have to be included in the Navier-Stokes equations. In usual numerical treatments of solving the equations of motion these non-inertial forces are included explicitly as source terms. In this letter we show that this procedure, if applied to the angular momentum equation, may lead to erroneous results. Using the specific sample calculation of a protoplanet embedded in a protostellar disk, we then demonstrate that only a conservative treatment of the Coriolis term in the angular momentum equation yields results which are identical to those obtained by computations performed in the inertial frame.