[G04-1] Earth rotation and geodynamics I

[G04-1-03] Geophysical interpretation of long-term polar motion

^○Jianli Chen (Center for Space Research, University of Texas at Austin, Austin, Texas, USA)

Polar motion represents the constant motion of the Earth rotation pole position in the terrestrial reference frame, and is driven by mass movement and redistribution within the Earth system, under the conservation of angular momentum. Polar motion has been accurately measured by a multi-technique observing program of international scope, with an accuracy reaching ~0.03 milliarcsecond (mas) over variations of up to few hundred mas. Observed polar motion at different temporal scales can be used to study mass changes in different components in the Earth system, including the atmosphere, ocean, hydrosphere, cryosphere and solid Earth. While at interannual and shorter time scales, polar motion is mainly driven by air and water mass redistribution and movement in the atmosphere, ocean and hydrosphere, ice mass change from polar ice sheets and mountain glaciers and non-steric global eustatic sea level change play an important role in driving polar motion at decadal and longer time scales. Solid Earth mass redistributions associated with Glacial Isostatic Adjustment (GIA) and tectonic movement are believed to be the dominated contributors to long-term polar motion (i.e., linear trends in most studied time frames). Using over 14-years of GRACE satellite gravity measurements and climate model predictions, here we provide a comprehensive analysis of geophysical excitations of polar motion from different components of the Earth system, with a focus on interannual and longer time scales. The extended record of GRACE time-variable gravity measurements offer a unique means for people to better understand geophysical excitations of polar motion at a broad band of frequencies, and provide observational constraints on model predicted polar motion excitations, such as those from GIA and pole tide (i.e., rotational deformation).