Mathematics – Logic
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007acasn..48..302z&link_type=abstract
Acta Astronomica Sinica, vol. 48, no. 3, p. 302-310
Mathematics
Logic
Earth: Dynamics, Astrometry: Earth Rotation
Scientific paper
The variation in the orientation of Earth's rotational axis with respect to Earth's figure axis is called polar wobble, which results from internal excitation processes, such as wind, current, pressure fluctuations in atmosphere, ocean and land--water, etc. The seasonal polar wobble has been confirmed to be largely caused by changes in atmospheric planetary angular momentum, due to atmospheric mass redistribution for periods between intra-seasonal time scale and a few years. However, the cause of the observed seasonal polar wobble is not fully understood. A growing body of evidence points to the oceans as one of the sources of much of the remaining excitation. In recent years, significant progresses have also been made in demonstrating the importance of ocean angular momentum (OAM) variability in explaining non-atmospheric polar wobble at periods of one year and shorter, with improvements in non-data assimilative and data assimilative ocean general circulation models (OGCM), as well as satellite radar altimeter observations. But compared with atmospheric angular momentum (AAM) determinations, OAM estimates remain relatively more problematic mainly due to scarce observations of the global oceans and large uncertainties in predictions of the ocean general circulation models. This paper contributes to this body of evidence by comparing effective OAM functions estimated from two improved assimilated models SODA_1.4.2 and SODA_1.4.3 to the non-atmospheric-hydrologic residual, which is the observed geodetic excitation function with atmospheric and hydrologic effects being removed. The Simple Ocean Data Assimilation (SODA) is recently developed at University of Maryland. For the seasonal fluctuation, the SODA assimilated effective OAM functions agree better with the non-atmospheric-hydrologic residual, than those estimated from the previous assimilated model SODA_Beta7, also for the annual variations. It has also been found that annual effective OAM vectors for SODA and ECCO in each latitude band are much closer along the Greenwich meridian, than along the 90° E meridian. Therefore, the oceanic and hydrologic roles in annual polar wobble should be further examined comprehensively.
Yan Hao-Ming
Zhong Ming
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