Discrepancies in the Earth-atmosphere angular momentum budget

Modern geodetic and atmospheric data sets have demonstrated that changes in the solid earth's rotation rate are closely coupled to changes in the atmosphere's angular momentum over a range of subseasonal through interannual time scales. Nevertheless, limits to the correspondence between changes in the momenta of the two bodies exist at both ends of the spectrum resolvable by the data. At high frequencies we show that changes in the length of day as short as a fortnight can now be attributed almost entirely to atmospheric forcing; more rapid fluctuations in the length of day, however, cannot be shown to coincide with atmospheric behavior, a result we blame mostly on errors remaining in both the geodetic and atmospheric series rather than on the neglect of some other component of the momentum budget. On the decadal time scale, nonatmospheric processes, believed primarily to involve core-mantle coupling, dominate the global momentum budget. Our analysis of the low frequency component of the difference between the momenta of the solid earth and atmosphere during 1976-1988 shows it to consist of a general trend interrupted by three major changes in slope. Whether this result indicates that core-mantle coupling is a nonsteady phenomenon or that unmodeled oceanic processes are responsible for the intermittency of the difference series is presently uncertain.