HR: 11:50h
AN: G42A-07    [Abstracts]
TI: Diurnal and Semidiurnal Signals in Polar Motion and UT1: Comparison of Space-geodetic Observations with Geophysical Models
AU: * Brzezinski, A
EM: alek@cbk.waw.pl
AF: Space Research Centre, Polish Academy of Sciences, Bartycka 18A, Warsaw, 00-716, Poland
AB: Polar motion and UT1 contain physical signals within the diurnal and semidiurnal frequency bands. The dominant part (< 1 milliarcsecond -- mas) is due to the gravitationally forced ocean tides. There is also a small variation (< 0.1 mas) due to the direct influence of the tidal gravitation on the triaxial structure of the Earth. The remaining part (< 0.1 mas) comprises the atmospheric and nontidal oceanic influences driven by the daily cycle in the solar heating. The observational evidence of diurnal and semidiurnal signals in polar motion and UT1 concerns mostly the purely harmonic ocean tide signals which are expressed by conventional models (IERS Conventions 2003). The continuous observation campaigns, like CONT94, CONT02, CONT05, have been also organized to estimate a less regular high frequency geophysical signals in Earth rotation and compare them with models. Our recent work (Bolotin and Brzezinski, 2006, Geophys. Res. Abstracts, Vol.8, EGU06-A-01665) demonstrated that it is also possible to extract the diurnal and semidiurnal signals in polar motion and UT1 extending over the last two decades, from reanalysis of the archived VLBI observations. An important independent estimation of such high-frequency signals in Earth rotation is from the global circulation models with subdiurnal resolution of the external geophysical fluids, the atmosphere and the oceans. Several atmospheric angular momentum series with 4-times daily sampling have been estimated on regular basis since 1992. Particularly important are the high- resolution reanalysis data sets extending back to 1948. Also, several subdaily time series of the nontidal oceanic angular momentum have been produced recently. This paper gives an overview of the recent advances in observation and modeling of polar motion and UT1 at diurnal and subdiurnal periods. I will focus attention on comparison between the estimates derived from the space- geodetic measurements and those computed from the high-resolution atmospheric and oceanic excitation data.
DE: 1223 Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions (0762, 1218, 3319, 4550)
DE: 1229 Reference systems
DE: 1239 Earth rotation variations
DE: 1295 Integrations of techniques
SC: Geodesy [G]
MN: 2007 Joint Assembly