Detection of different-time-scale signals in the length of day variation based on EEMD analysis technique

Scientists pay great attention to different-time-scale signals in the lengllh of day （LOD） variations △LOD, which provide signatures of the Earth＇s interior structure, couplings among different layers, and potential excitations of ocean and atmosphere. In this study, based on the ensemble empirical mode decomposition （EEMD）, we analyzed the latest time series of △LOD data spanning from January 1962 to March 2015. We observed the signals with periods and amplitudes of about 0.5 month and 0.19 ms, 1.0 month and 0.19 ms, 0.5 yr and 0.22 ms, 1.0 yr and 0.18 ms, 2.28 yr and 0.03 ms, 5.48 yr and 0.05 ms, respectively, in coincidence with the results of predecessors. In addition, some signals that were previously not definitely observed by predecessors were detected in this study, with periods and amplitudes of 9.13 d and 0.12 ms, 13.69 yr and 0.10 ms, respectively. The mechanisms of the LOD fluctuations of these two signals are still open.

Interannual variations in length of day and atmospheric angular momentum, and their seasonal associations with El Ni^o/Southern Oscillation-like sea surface temperature patterns

This study examines the seasonal connections between the interannual variations in LOD （length of day）/ AAMglobe （the relative atmospheric angular momentum for the whole globe） and the ENSO-like SST （El Nifio/ Southern Oscillation-like sea surface temperature） pattern and corresponding zonal and vertical circulations. Consistent with previous studies, the ENSO-like SST impact the following season LOD/AAMglobe, with the strongest correlations in DJF （December, January, and February）, when it is likely to be the peak E1 Nino/La Nifia period. Lag correlations between the interannual variations in LOD/AAMglobe and surface temperature, and the interannual variations in LOD and both zonal circulation and vertical airflow around the equator, consistently indicate that the LOD/AAMglobe reflect the potential impacts of variations in the Earth＇s rotation rate on the following season＇s sea surface temperatures （SST） over the tropical central and eastern pattern is located）. Pacific （where the ENSO-like SST Moreover, the centers of strongest variation in the AAMcolumn （the relative atmospheric angular momentum for an air column and the unit mass over a square meter） are located over the mid-latitudinal North Pacific in DJF and MAM （March, April, and May）, and over the mid-latitudinal South Pacific in JJA （June, July, and August） and SON （September, October, and November）. This suggests that the AAMcolumn over the mid-latitudinal Pacific around 30°N （30~S） dominate the modulation of Earth＇s rotation rate, and then impact the variations in LOD during DJF and MAM （JJA and SON）.