The Impact on UT1 Predictions of AAM, OAM, and HAM Forecasts

In support of the operational tracking and navigation of interplanetary spacecraft, a Kalman filter has been used at the Jet Propulsion Laboratory (JPL) for nearly three decades to combine independent measurements of the Earth's orientation and to predict its future evolution. Short-term predictions of UT1 are improved when dynamical model-based analyses and forecasts of the axial component of atmospheric angular momentum (AAM) are used as proxy length-of-day measurements and forecasts. Such AAM analyses and forecasts are computed from products generated as part of the numerical weather prediction activities at governmental agencies like the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF). At JPL, AAM forecasts from NCEP are currently used to operationally predict UT1. Here the accuracy of JPL's short-term UT1 predictions produced during 01 November 2010 to 30 April 2011 using the NCEP forecasts are compared to the accuracy of the UT1 predictions that would have been produced if ECMWF forecasts had been used instead. The impact on UT1 predictions of additionally incorporating forecasts of oceanic and hydrologic angular momentum is also evaluated.