From Inter-decadal to multi-decadal variations at length of day.

The instability in Earth's rotation can be measured through the changes in rotation period, which is the length of day (LOD). The atmospheric excitations, the eustatic variation in sea level, and the nonlinear ENSO oscillation have been evaluated and correlate well with the observed changes in LOD. The long-period metrological influence on LOD is reported. However, it has limited effects at the decadal timescale. An inter-decadal variation ( 6 years) oscillation is found, which may be excited by the torsional wave associated with geomagnetic jerks (Holme and de Viron, 2013). We independently isolated the time variation at LOD from inter-decadal to multi-decadal variation at LOD. The LOD oscillation 6 years period is confirmed again, and besides, we will pay particular attention to the multi-decadal variations at LOD and the driving mechanisms behind it.