New evidences for the fluctuation characteristic of intradecadal periodic signals in length-of-day variation

TL;DR

This study provides robust evidence that intradecadal oscillations in length-of-day variations are stable, identifies a new 7.6-year signal, and suggests geomagnetic jerks as possible excitation sources for these oscillations.

Contribution

It demonstrates the stability of intradecadal oscillations since 1962, identifies a new 7.6-year periodic signal, and links geomagnetic jerks to these oscillations as potential excitation sources.

Findings

No stable damping trends for SYO and EYO since 1962.

Identification of a new 7.6-year periodic signal.

Geomagnetic jerks are likely excitation sources for the oscillations.

Abstract

The intradecadal fluctuations in the length-of-day variation (dLOD) are considered likely to play an important role in core motions. Two intradecadal oscillations, with 5.9yr and 8.5yr periods (referred to as SYO and EYO, respectively), have been detected in previous studies. However, whether the SYO and the EYO have stable damping trends since 1962 and whether geomagnetic jerks are possible excitation sources for the SYO/EYO are still debated. In this study, based on different methods and dLOD records with different time span, we show robust evidences to prove that the SYO and the EYO have no stable damping trends since 1962, and we find that there is also a possible 7.6yr signal. To prove whether it is a periodic signal, we use the optimal sequence estimation method to stack 35 global geomagnetic records, the results also show an 7.6yr periodic signal which has an Y2,-2 spatial distribution, and it has a high degree of consistent synchronicity with the 7.6yr signal in dLOD. After confirming that the jerks have no special consistency with the peaks/valleys of the EYO/SYO, we confirm that the geomagnetic jerks seem to be related to sudden changes in the SYO/EYO time series and their excitation series; so we finally suggest that jerks are possible excitation sources of the SYO/EYO. Meanwhile, after using a deconvolution method, we estimate that the period P and quality factor Q of the SYO and the EYO are [P=5.85+/-0.06yr, Q larger than 180] and [P=8.455+/-0.17yr, Q larger than 350], respectively.