Global Mapping of the Nonstationary Semidiurnal Internal Tide Using Argo Data

Abstract

Data from Argo floats equipped with Iridium communications are used to obtain a global map of the total amplitude (or variance) of the semidiurnal internal tide at 1,000 dbar. The results are confirmed by a comparison with data from an historical collection of moored instruments. The obtained amplitude is in turn compared with the High-Resolution Empirical Tide (HRET) model, based on satellite altimetry. While HRET only contains the stationary component, with a fixed phase difference to the astronomical tide, the present results capture the total amplitude, including the nonstationary component. We estimate the global average ratio of total (Argo) to stationary (HRET) semidiurnal internal tide variance to be 6.5, and the amplitude ratio to be 3.6. Our estimate of the stationary fraction of the semidiurnal internal tide is subject to significant uncertainties. In particular, HRET is thought to mainly represent baroclinic mode-1 waves, while Argo data contain contributions from all modes.