Seasonal excitation of polar motion estimated from recent geophysical models and observations

Abstract

Seasonal excitation of polar motion estimated from recent geophysical models and observations. Journal of Geodynamics, Elsevier, 2009, 48 (3-5) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Page 1 of 8A c c e p t e d M a n u s c r i p t AbstractHere we investigate the seasonal excitation balance of polar motion using recent geophysical data sets and models. Attention is focused on the contribution of the land hydrology which is expressed either by models, such as CPC, GLDAS, LaD, or by the observations provided by the experiment GRACE. Geophysical excitation series are compared to each other and to the excitation inferred from the space geodetic observations of polar motion. Comparison shows that 3 models of land hydrology considered in this work differ considerably; adding the corresponding excitation series to the combination of atmospheric and oceanic excitation data does not clearly improve agreement with observations. But combination of the GRACE-derived mass term of excitation with the motion terms of atmospheric and oceanic excitations brings the excitation balance considerably closer in case of the retrograde/prograde annual and retrograde semiannual components of polar motion. For other seasonal components as well as for the nonharmonic residuals, the estimated contributions of hydrology do not improve the excitation balance of polar motion.

Hydrological excitation of polar motion by different variables from the GLDAS models

“…Nevertheless, the sum of AAM and OAM does not entirely explain the observed variations of polar motion (Ponte et al 1998;Nastula and Ponte 1999;Brzeziński et al 2009). The remaining power might be provided by the hydrological angular momentum (HAM).…”

“…8a, b). We computed these prograde and retrograde components of polar motion excitation functions, χ 1 + iχ 2 for each of the considered hydrological and gravimetric excitation functions and for the GAO using the least squares method (Brzeziński et al 2009). The fitted model comprises the second order polynomial and the sum of complex sinusoids with periods of 365.25, 180.0 and 120.0 days.…”

“…However, because these geophysical processes are very complex, these models still suffer from uncertainties in the process descriptions, parametrizations and forcing (Güntner 2008). Consequently, estimates of the excitation of the Earth's rotation derived from geophysical models are also affected by uncertainties (Gross et al 2003;Seitz and Schmidt 2005;Nastula et al 2007Nastula et al , 2011Brzeziński et al 2009;Dobslaw et al 2010).…”

“…The EWT patterns from GRACE are subject to the removal of artifacts by de-striping, filter smoothing methods and are also subject to aliasing errors (Jin et al 2010). Several centers, such as the GeoForschungsZentrum (GFZ), the Center for Space Research (CSR) and the Jet Propulsion Laboratory (JPL) have computed the coefficients of series of timevariable gravitation and of the adequate layer of water storage (Brzeziński et al 2009;Seoane et al 2009). In this study, we used the GRACE data of RL05 series as computed by the CSR.…”

Earth Rotation Variations – Long Period

“…For example, the individual effects on the Earth's rotation of changes in the mass distribution of the oceans (e.g., G€ ottl et al, 2012;Jin et al, 2010) and of water stored on land (e.g., Brzezinski et al, 2009;Fernández, 2009;Jin et al, 2010Jin et al, , 2012Seoane et al, 2011) can be studied with GRACE measurements after atmospheric effects are removed from them using a model. For example, the individual effects on the Earth's rotation of changes in the mass distribution of the oceans (e.g., G€ ottl et al, 2012;Jin et al, 2010) and of water stored on land (e.g., Brzezinski et al, 2009;Fernández, 2009;Jin et al, 2010Jin et al, , 2012Seoane et al, 2011) can be studied with GRACE measurements after atmospheric effects are removed from them using a model.…”