DETECTION OF AN ENSO SIGNAL IN SEASONAL LENGTH-OF-DAY VARIATIONS

Conservation of angular momentum dictates that as the wind-driven axia l atmospheric angular momentum changes, so will the length-of-day (LOD ). In particular, as the strength of the seasonal zonal winds change, so should the strength of the seasonal LOD signals. Here, observed cha nges in the strengths of the annual and semiannual LOD signals during 1963-1991 are analyzed and shown to be both significantly correlated ( at the 99% significance level) with the Southern Oscillation Index (SO I), and to exhibit trends of comparable magnitude but opposite signs. This reported correlation between the SOI and changes in the amplitude of the seasonal LOD signals demonstrates a linkage between seasonal L OD (and hence seasonal zonal wind) variability and the El Nino / South ern Oscillation (ENSO) phenomenon. Furthermore, this study suggests th at observed variations in the amplitudes of the seasonal LOD signals c an be used to study changes in the strengths of the seasonal atmospher ic zonal winds on interannual to decadal and longer time scales.