Pseudo-120d Variations in Length-of-Day from 1950-2003 with El Nino

The time-frequency variations of the geodetic and atmospheric induced pseudo-120-day length-of-day changes(ΔLOD) from 1950 to 2003 are studied by a wavelet amplitude spectrum method,and they are compared with the inter-annual variation(2 to 6 years) of sea surface water temperature anomaly(SSTA) in Regions 3,4 of El Nino.The results show that the amplitude of the pseudo-120-day ΔLOD reaches its relative summit when an El Nino above the 4-year period occurs,except for the atmospheric induced case in 1966.In addition,it is also found that there is a uniform change in the time-frequency figures of pseudo-120-period ΔLOD between the scale of 80 days and 110 days,and in the time-frequency figure of El Nino events below the 4-year period.All of these results indicate that the amplitude variations of the pseudo-period LOD changes at the scale of 80-120 days are modulated by El Nino events.