Data of Core Angular Momentum Changes

The zonal toroidal t_1^0 and t_3^0 components of a fully time-dependent geostrophic flow constructed under the frozen flux hypothesis are used to estimate the core angular momentum (CAM) using the hypothesis of Jault Gire and Le Mouel (1988). The CAM is then transformed into an equivalent change in the length of day as seen  on the solid Earth by conservation of angular momentum. The predictions only give relative changes in the lod, therefore an arbitrary offset should be chosen in order that the predictions agree reasonably well with the lod series from astronomical observations. A value of 3.25 milliseconds has been added to the predictions to give the values presented here.

Description of the data used for model computation :

Column '1'
Date

Column '2' and '3'
Zonal toroidal coefficients of the surface angular velocity respectively of degree one and three of an expansion in Legendre Polynomials (unit = degree / year).

Column '4'
Integrated angular velocity of the Earth core (unit = degree / year) in a frame of reference rotating at the (variable) mantle angular spin rate. The surface velocity field has been derived from different secular variation models calculated with different truncations and regularizations.

References to be mentioned when data are used :
Jault D., Gire C., and Le Mouël J.-L., 'Westward drift, core motions and exchanges of angular momentum between core and mantle', Nature, 333, 353-356, #1988.

Related references :

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