GoKawiil
Tech News
Researchers Hao Zhang and Mathieu Dumberry report in Nature that gravitational coupling between Earth's solid inner core and its mantle explains multidecadal changes in day length of a few milliseconds. They combined seismological data on inner-core rotation with a model of outer-core flow derived from magnetic field measurements to reach this conclusion.
A study published in Nature reports that small variations in the length of Earth's day, on the order of milliseconds over decades, can be explained by competing gravitational, mechanical and electromagnetic forces between Earth's solid inner core, molten outer core and rocky mantle. Researchers, including geophysicist Mathieu Dumberry, had long suspected core-mantle interactions caused these fluctuations but lacked clarity on which specific forces were responsible.
Researchers analyzed length-of-day (LOD) records from 1964 to 2019, after removing known effects from the atmosphere, oceans, tides and surface mass changes, to isolate multidecadal variations. They modeled these residual variations using torque equations that account for gravitational pull from the inner core alongside electromagnetic and topographic coupling at the core-mantle boundary, finding that gravitational torque from the inner core contributes to the slow, multidecadal changes in how long a day lasts.