Space geodetic techniques have provided high-precision measurement of daily variations in the Earth’s spin rate -- characterized by the Length of Day (LOD) -- and the spin axis position relative to the crust, termed Polar Motion (PM). Before the advent of the space era, astronomers and geophysicists have inferred the change in LOD for the past three millennia from eclipse records and the PM for over a century from star catalogs. In this talk, I will summarize our ongoing efforts to understand and disentangle various driving mechanisms of the Earth’s rotation parameters across timescales and highlight the increasingly dominant role of ongoing climate change. By leveraging observations of Earth’s surface mass distribution, state-of-the-art climatological and geophysical models, and a novel approach of the Physics Informed Neural Networks (PINNs), we show that the sustained melting of glaciers and ice sheets not only alters the long-term drift direction of the spin axis but also exhibits a strong control in slowing down the spin rate. These findings have broad implications for constraining various geophysical and climatological processes and exploring their possible interactions.

Surendra Adhikari is a research scientist at JPL’s Earth Surface and Interior group. He works at the intersection of climate science (e.g., glacier mechanics, sea-level variability) and solid Earth geophysics (e.g., glacial isostatic adjustment, Earth’s gravitation and rotation). Surendra is currently a member of the NASA Sea-level Change Team, Solid Earth Team, and the GRACE-FO Science Team. His work has been recognized with a 2019 NASA Early Career Achievement Medal and a 2021 AGU John Wahr Early Career Award.