Considerations concerning the non-rigid Earth nutation theory

This paper presents the reflections of the Working Group of which the tasks were to examine the non-rigid Earth nutation theory. To this aim, six diff erent levels have been identified: Level 1 concerns the input model (giving profiles of the Earth's density and theological properties) for the calcul ation of the Earth's transfer function of Level 2; Level 2 concerns the int egration inside the Earth in order to obtain the Earth's transfer function for the nutations at different frequencies; Level 3 concerns the rigid Eart h nutations; Level 4 examines the convolution (products in the frequency do main) between the Earth's nutation transfer function obtained in Level 2, a nd the rigid Earth nutation (obtained in Level 3). This is for an Earth wit hout ocean and atmosphere; Level 5 concerns the effects of the atmosphere a nd the oceans on the precession, obliquity rate, and nutations; Level 6 con cerns the comparison with the VLBI observations, of the theoretical results obtained in Level 4, corrected for the effects obtained in Level 5. Each level is discussed at the state of the art of the developments.