ANALYTICAL COMPUTATION OF MODES FOR AN EARTH WITH VISCOUS BOUNDARY-LAYERS, AND INFLUENCE OF VISCOSITY ON THE NONROTATING SLICHTER PERIOD

In this paper, we want to extend an alternative working method (Degrys e and Dehant, 1993) for determining analytically core modes and freque ncies of core oscillations to a non-rotating spherically symmetric Ear th that might be compressible and that has a radially dependent viscos ity. Since the viscosity of the outer core is considered to be small, an appropriate way to study its impact is by using boundary-layer theo ry (Van Dyke, 1964; Kevorkian and Cole, 1981). The representation of n umerical values of eigenperiods is focused on the eigenperiod of the p rincipal translational (Slichter, 1961) mode of free oscillation of th e solid inner core. For a sma;ll value of the outer core viscosity of the order of 10-(10)kg/(ms), we obtained a non-rotating Slichter perio d of 4.886 hr, which only slightly differs from the result of the non- viscous case. For an increasing viscosity, the eigenperiods will sligh tly increase.