Detection of an ENSO signal in seasonal length‐of‐day variations

Conservation of angular momentum dictates that as the wind-driven axial 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 changes 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 (SOI), 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 LOD (and hence seasonal zonal wind) variability and the El Nino/Southern Oscillation (ENSO) phenomenon. Furthermore, this study suggests that observed variations in the amplitudes of the seasonal LOD signals can be used to study changes in the strengths of the seasonal atmospheric zonal winds on interannual to decadal and longer time scales.

[1]  Michael Ghil,et al.  El Ni�o on the Devil's Staircase: Annual Subharmonic Steps to Chaos , 1994, Science.

[2]  T. W. Anderson.  An Introduction to Multivariate Statistical Analysis , 1959 .

[3]  R. Rosen,et al.  Contribution of stratospheric winds to annual and semiannual fluctuations in atmospheric angular momentum and the length of day , 1985 .

[4]  J. Dickey,et al.  The oceanic contribution to the Earth's seasonal angular momentum budget , 1993 .

[5]  S. Philander,et al.  Secular Changes of Annual and Interannual Variability in the Tropics during the Past Century , 1995 .

[6]  B. Chao.  Correlation of interannual length‐of‐day variation with El Niño/Southern Oscillation, 1972–1986 , 1988 .

[7]  Klaus Fraedrich,et al.  Estimating the Dimensions of Weather and Climate Attractors , 1986 .

[8]  Fluctuations in the Earth's rotation since 1830 from high-resolution astronomical data , 1994 .

[9]  Eli Tziperman,et al.  Irregularity and Locking to the Seasonal Cycle in an ENSO Prediction Model as Explained by the Quasi-Periodicity Route to Chaos , 1995 .

[10]  E. Rasmusson,et al.  Variations in Tropical Sea Surface Temperature and Surface Wind Fields Associated with the Southern Oscillation/El Niño , 1982 .

[11]  I. Naito,et al.  A seasonal budget of the Earth's axial angular momentum , 1990 .

[12]  R. Rosen.  The axial momentum balance of Earth and its fluid envelope , 1993 .

[13]  Bin Wang,et al.  Interactions between the Seasonal Cycle and El Niño-Southern Oscillation in an Intermediate Coupled Ocean-Atmosphere Model , 1995 .

[14]  Bin Wang,et al.  Interactions between the seasonal cycle and the Southern Oscillation - Frequency entrainment and chaos in a coupled ocean-atmosphere model , 1994 .

[15]  J. Dickey,et al.  Earth's Variable Rotation , 1991, Science.

[16]  R. Rosen,et al.  Comment on ″A seasonal budget of the Earth's axial angular momentum″by Naito and Kikuchi , 1991 .

[17]  I. Naito,et al.  Reply to Rosen & Salstein's Comment , 1991 .

[18]  B. Chao.  WITH RELATION TO THE SOUTHERN OSCILLATION/EL NINO , 1984 .

[19]  Eli Tziperman,et al.  El Ni�o Chaos: Overlapping of Resonances Between the Seasonal Cycle and the Pacific Ocean-Atmosphere Oscillator , 1994, Science.

[20]  T. Eubanks,et al.  The El-Nino, the Southern Oscillation and the Earth Rotation , 1986 .

[21]  R. Vautard,et al.  Singular spectrum analysis in nonlinear dynamics, with applications to paleoclimatic time series , 1989 .

[22]  G. P. King,et al.  Extracting qualitative dynamics from experimental data , 1986 .

[23]  Xuguang Wang,et al.  The Coupling of the Annual Cycle and ENSO Over the Tropical Pacific , 1994 .