A study of Global Wind Structure Exciting the Chandler Wobble

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The Chandler wobble (hereafter CW), a free oscillation of the Earth's pole with the longest period among the Earth's free oscillations. However, its excitation source has never been identified since its discovery more than a hundred years ago. Lately, the author and collaborators have found its excitation source to be wind from its evaluations based upon global atmospheric analysis data from numerical weather prediction system of the Japan Meteorological Agency. Since there are two kinds of data setin the analysis data (initialized and un-initialized data), they also pointed out a possibility that the evaluations depend upon the analysis data used for. In this study, the author reevaluated atmospheric excitation of CW based on the two kinds of the ECMWF reanalysis data for the period of 1980-1994, and reconfirmed wind to be the CW source. The wind excitation reconfirmed here totally opposes the oceanic excitation proposed lately. Interesting is a fact that CW is excited by the wind variation with a remarkable peak at near the CW frequency in its power spectrum. Also, the differences in the used two analysis data have almost no effect on the evaluations for the CW excitation, though they strongly affect the excitatlbn for the annual wobble.