Global and regional axial ocean angular momentum signals and length-of-dayvariations (1985-1996)

Changes in ocean angular momentum nl about the polar axis are related to fl uctuations in zonal currents (relative component M-r) and latitudinal shift s in mass (planetary component M-Omega). Output from a 10 ocean model is us ed to calculate global M-r, M-Omega, and M time series at 5 day intervals f or the period January 1985 to April 1996. The annual cycle in M-r, M-Omega, and M is larger than the semiannual cycle, and M-Omega amplitudes are near ly twice those of M-r. Year-to-year modulation of the seasonal cycle is pre sent, but interannual variability is weak. The spectrum of M is red (backgr ound slope between omega(-1) and omega(-2)) at subseasonal periods, implyin g a white or blue spectrum for the external torque on the ocean. Comparison s with previous studies indicate the importance of direct atmospheric forci ng in inducing subseasonal M signals, relative to instabilities and other i nternal sources of rapid oceanic signals. Regional angular momentum estimat es show that seasonal variability tends to be larger at low latitudes, but many local maxima exist because of the spatial structure of zonal current a nd mass variability. At seasonal timescales, latitudes similar to 20 degree s S-10 degrees N contribute substantial variability to M-Omega, while signa ls in M-r can be traced to Antarctic Circumpolar Current transports and ass ociated circulation. Variability in M is found to be small when compared wi th similar time series for the atmosphere and the solid Earth, but ocean si gnals are significantly coherent with atmosphere-solid Earth residuals, imp lying a measurable oceanic impact on length-of-day variations.