The solid Earth's rotation varies slightly with time due to geophysical processes that involve motions and redistributions of mass occurring on or within the Earth, as dictated by the conservation of angular momentum. In particular, these variations Δ LOD) in the atmosphere in terms of the axial atmospheric anglar momentum (AAM) are the primary cause for nontidal length-of-day variations on timescales of several days to several years [e.g., Rosen, 1993]. Here Δ LOD is a convenient measure of Earth's rotational speed relative to the uniform time kept by atomic clocks.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.