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Abstract

The rotation of the Earth changes in response to the action of torques acting on the Earth from both gravitational effects of other bodies of the solar system and interactions with all the geophysical fluids. The response of the Earth to these torques can be described using angular momentum conservation involving mass distribution in the Earth in a frame of reference fixed to the Earth. The long-term, interdecadal, intra-decadal, and decadal variations in length of day (LOD) could have several possible driving mechanisms. On the one hand, there is the external forcing such as the gravitational attraction from the Sun, Moon, and other planets acting on the solid Earth mainly explaining long-term variations, and on the other hand, there exist torques induced by the atmosphere, ocean, and hydrology circulation, mainly causing small-period changes in the Earth rotation. Using the atmosphere, ocean, and hydrology observations, it is possible to model their contributions to the Earth’s rotation change through the angular momentum approach. Furthermore, the large-scale surface mass transport such as the glacial isostatic adjustment and polar icecap melting, etc. all slightly modify the global shape of Earth, as well as alter the rotation speed in a linear way at the long-term and decadal time scale. In addition, the core-mantle processes must be involved to explain the decadal oscillation measured in LOD, typically processes involving large-scale fluid motions in the liquid outer core. We study the various periodical oscillations in the historical data and the IERS C04 LOD products as well.