An estimate of the water storage contribution to the excitation of polar motion

Abstract

The major source of the excitation of the Chandler wobble has not yet been established but is believed to be primarily meteorological in origin. Previous studies of the meteorological excitation of the Chandler wobble have measured only effects from motions in the atmosphere and the oceans. The role of global water storage has been regarded as unimportant because of its relatively minor role in the excitation of the annual wobble. In addition, an appropriate hydrological dataset has not been readily available for global measurements of an extended monthly time series of the water storage contribution to the Chandler wobble's excitation. Thus, an evaluation of the contribution has never been attempted. However, a crude estimate of the global water storage series is possible using worldwide records of monthly precipitation and temperature, accumulating precipitation at individual locations whenever temperatures are at 0°C or below. Comparison of this modelled series with a previous estimate of the annual component of the global water balance, and with the observed monthly polar motion series, indicates good agreement with the former, and a significant correlation with the latter near the Chandler frequency. Combining the estimated water storage series with a previously computed atmospheric excitation series produces better Chandler frequency coherence with the ILS polar motion data than is obtained with either series separately. Copyright © 1987, Wiley Blackwell. All rights reserved