Oceanic excitations on polar motion: a cross comparison among models

• Published in: Geophysical journal international Vol. 162; no. 2; pp. 390 - 398
• Main Authors: Zhou, Y. H., Chen, J. L., Liao, X. H., Wilson, C. R.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.08.2005; Blackwell Science Ltd
• Subjects: excitation; ocean general circulation model (OGCM); oceanic angular momentum (OAM); polar motion; polar motion; oceanic angular momentum (OAM); excitation; ocean general circulation model (OGCM)
• ISSN: 0956-540X; 1365-246X
• DOI: 10.1111/j.1365-246X.2005.02694.x

Recent studies based on various ocean general circulation models (OGCMs) demonstrate that the oceans are a major contributor to polar motion excitations. In this paper, we analyse and compare observed non-atmospheric polar motion excitations with oceanic angular momentum (OAM) variations determined from four OGCMs, which include the parallel ocean climate model (POCM), a barotropic ocean model (BOM), the Estimating the Circulation and Climate of the Ocean (ECCO) non-data-assimilating model (ECCO-NDA) and the ECCO data-assimilating model (ECCO-DA). The data to be analysed span a 5-yr overlapped period from 1993 to 1997. At annual timescale, considerable discrepancies exist between POCM and the other three models, which result mainly from differences in annual components of the forcing wind fields. At semi-annual timescale, however, POCM shows better phase agreement with observed non-atmospheric polar motion excitation than the other three ocean models. At intraseasonal timescales, ECCO-DA yields better agreement with observations, and reduces the variance of non-atmospheric excitations by ∼60 per cent, 10–20 per cent more than those explained by the other three models. However, at the very short periods of 4–20 days, the BOM estimates could explain about half of the observed variance, twice as much as that by ECCO-NDA, and also shows considerably better correlation with observations. Due to different modelling schemes and methods, significant discrepancies could arise with respect to the quality of modelling large-scale oceanic mass redistribution and current variation. A complete understanding of global oceanic contributions to polar motion excitation still remains a challenge.