Abstract
Atmospheric wind and pressure contributions to non‐seasonal variations in the length of day (LOD) determined by the International Radio Interferometry Surveying are evaluated during the years of 1984–1991 using Japan Meteorological Agency data that include winds up to 10mb. We confirm that intra‐annual LOD variations are the result of tropospheric zonal wind changes, which include a pronounced quasi‐seven month oscillation in addition to the well‐known intra‐seasonal oscillation. It is also shown that inter‐annual LOD variations on time scales of two to five years are the superposed contributions from both a stratospheric quasi‐biennial oscillation and tropospheric low frequency variations of two‐to‐five year time scales in zonal wind. The residual LOD after removing these atmospheric contributions shows a decadal‐like variation, which may be caused by a core ‐ mantle coupling torque.
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