Excitations of Polar Motion from an Ensemble of Global Atmospheric Models

Abstract

We study how atmospheric models can be best used to understand excitations of polar motion. The set of models consists of those contributed worldwide by meteorological centers participating in the Atmospheric Model Intercomparison Project, which are forced solely by a prescribed distribution of sea surface temperatures. We have calculated the monthly mean values of excitations from the resulting surface pressure fields over the 17-year study period. With such historical variability and with the spread inherent in the suite of models, a measure of the excitations of polar motion can be obtained, including variability at intraseasonal and seasonal scales; from these models we can also view the resulting interannual variability, including the impact of El Nino events. We compare the results with the excitations determined by atmospheric analyses, as well as with the geodetic excitation functions themselves, determined from analysis of observations. Based on the suite of atmospheric models we estimate the spread in the polar motion excitation from the ensemble of 19 different models.