MEAN ELECTROMOTIVE-FORCE DUE TO MAGNETOCONVECTION IN ROTATING HORIZONTAL LAYER IN DEPENDENCE ON BOUNDARY-CONDITIONS

The instability due to a vertical uniform temperature gradient is studied in a rapidly rotating horizontal layer of an electrically conducting fluid permeated by an azimuthal magnetic field linearly growing with the distance from the vertical axis of rotation. In addition to the boundary conditions used ill Soward's study (1979), that is, force-free surface and perfect electrical and thermal conductivity outside, also other conditions more realistic for the Earth's core are considered, that is, rigid surface aid electrically insulating walls. Using the concept of mean-field mhd mean electromotive and ponderomotive forces (E.M.F. and P.M.F.) are calculated and compared for various boundary conditions. The dependence of the E.M.F. and. P.M.F. on the electromagnetic boundary conditions is strong (slight) if the boundaries are free (rigid).