Improved Models for Precession and Nutation

The modeling of nutations and precession has advanced to the point where the rms of residuals between theory and the observational estimates from the VLBI data of the past decade is only 0.16 mas in sin 0 as well as in . Such a t is provided by the MHB2000 nutation series (Mathews et al., 2000) based on geophysical theory with a few basic Earth parameters estimated by a t to nutation-precession data, and its accompanying precession rate. A brief account of the series is presented, along with an outline of the theoretical background and of the geophysical information of interest obtained in the process of constructing the series. A series due to Shirai and Fukushima (2000) also gives a somewhat comparable t to data, improving on the IERS 1996 series, but it is essentially empirical and provides no geophysical insights.