## Reply to the Comment by Y. Ricard, R. Sabadini and G. Spada

**J. Moser** ** , **
**David A. Yuen** ** & **
**Ctirad Matyska**
### Summary

We welcome this opportunity which Drs. Ricard, Sabadini and Spada (RSS)
have offered us to elaborate several points on the relationship between
convective circulations and rotational dynamics. First of all, mantle
convection is a non-linear fluid dynamical phenomenon with some form of
non-linear rheology. The usage of linear viscoelastic modes cannot hope to
capture many of the complex features in mantle convection, such as the
catastrophic flushing events. The relationship of the linear viscoelastic
normal-mode theory to other approaches, such as viscous and the non-linear
viscoelastic treatments, can be found in Moser et al. (1993). In this reply
we will address the issues raised by RSS by first going over the reference
system. This will be followed by a discussion concerning long-term polar
wander and relative angular momentum. Then we go over the issues concerning
the off-diagonal terms in the total moment of inertia and polar wander.
Finally, the limitations of the normal-mode approach used by RSS are
pointed out within the context of recent developments in geophysics.

Geophys. Res. Lett., **20** (1993), 2497-2498.