ON THE RADIATIONAL ANOMALY IN THE GLOBAL OCEAN TIDE WITH REFERENCE TOSATELLITE ALTIMETRY

The increasing precision of satellite altimetry in relation to tides j ustifies making a distinction between the gravitationally generated S- 2 tide and its observed values in the ocean, which are affected indire ctly by solar radiation. In view of the relatively high noise backgrou nd, we propose a simplified form of response analysis in which the pur ely solar semidiurnal harmonics of the gravitational potential are mod ified by an arbitrary amplitude-factor R and a phase lag r*. Analysis of a globally representative set of 80 tide-recording stations shows that the observed S-2 constituent is strongly coherent with its gravit ational part deduced from lunar tides, with regression constants R = 0.97, r = 5.9 degrees. The corresponding 'radiational anomaly has a p hase lag of 108 degrees on the gravitational part, with amplitude rati o 0.105, very close to the values associated with the inverse barometr ic tide. The proposed analytical procedure should yield improved defin ition of S-2 and K-2 when applied to altimetry from either sun-synchro nous or non-sun-synchronous satellites. This result is confirmed by co mparing an analysis of 40 cycles of Topex/Poseidon altimetry with 'sea truth' from 30 open-sea tide-gage stations.