Periodical Characteristics of the Geomagnetic Secular Variation and Decadal Length‐of‐Day Variation

Abstract Based on the historical geomagnetic model GUFM1 and the 10th International Geomagnetic Reference Field models (IGRF10) and the length‐of‐day data series, the wavelet transform method is used to analyze secular variation of various geomagnetic parameters such as geomagnetic moment and its energy and westward drift etc. And the periodical components as well as time‐varying characteristics of the decadal length‐of‐day variation are also under investigation. As the results suggest, during the period of 1800~2005, the 82‐year and 48‐year quasiperiodic components are available for the secular variation of dipole magnetic field, which are not directly related to the periodicity of the length‐of‐day variation. And both the 66‐year and 32‐year quasi‐periodic components are found for the secular variation of non‐dipole magnetic field parameters and length‐of‐day variation, and the 66‐year quasi‐periodicity is stronger than the 32‐year one. As far as the 66‐year quasi‐periodic component is concerned, the westward drift exceeds the length‐of‐day 8.8 years; and the non‐dipole magnetic field energy lags behind the length‐of‐day 15.6 years. We consider that there is no relationship between cause and effect for the decadal length‐of‐day fluctuation and geomagnetic secular variation.