Diurnal/semidiurnal polar motion excited by oceanic tidal angular momentum

The axial component of the oceanic tidal angular momentum (OTAM) has been demonstrated to be responsible for most of the diurnal and semidiurnal variations in Earth's rotational rate. In this paper we study the equatorial components of OTAM and their corresponding effects on the orientation of Earth's rotational axis, or polar motion. Three ocean tide models derived from TOPEX/Poseidon satellite altimetry are employed to predict the polar motion excited by eight major diurnal/semidiurnal tides (Q(1), O-1, P-1, K-1, N-2, M(2), S-2, K-2). The predictions are compared with geodetic measurements of polar motion from both long-term observations and during the intensive campaign Cont94. The prograde diurnal and prograde and retrograde semidiurnal periods are treated, whereas the retrograde diurnal polar motion is not treated (because it cannot be observed directly and uniquely.) The comparison shows generally good agreement, with discrepancies typically within 10-30 micro-arc-seconds for the largest tides. The eight tides collectively explain nearly 60% of the total variance in subdaily polar motion during Cont94. This establishes the dominant role of OTAM in exciting the diurnal/semidiurnal polar motion and paves the way for detailed studies of short-period nontidal polar motion. The present accuracy, however, is inadequate to shed light on the prograde diurnal polar libration.