Day length fluctuations

The length of the day (LOD), which has increased over the long term of Earth's history due to tidal effects, is also subject to fluctuations on a shorter scale of time.

Exact measurements of time by atomic clocks and satellite laser ranging have revealed that the LOD is subject to a number of different changes.

Internal torques are due to relative movements and mass redistribution of Earth's core, mantle, crust, oceans, atmosphere, and cryosphere.

Crustal movements (such as continental drift) or polar cap melting are slow secular (non-periodic) events.

[7] One means of exchange of angular momentum between the atmosphere and the non gaseous parts of the earth is evaporation and precipitation.

Any net global transfer of water mass from oceans to the atmosphere or the opposite implies a change in the speed of rotation of the solid/liquid Earth which will be reflected in LOD.

[8] The zonal wind of this component has the amplitude u at the equator relative to the ground, where u > 0 indicates superrotation and u < 0 indicates retrograde rotation with respect to the solid Earth.

Any short term fluctuation of the rigidly rotating zonal wind-component is then accompanied by a corresponding change in LOD.