Global mapping of the nonstationary M2 internal tide using Argo data

Data from Argo floats equipped with Iridium communications are used to obtain a global map of the total amplitude (or variance) of the M₂ internal tide. The results are confirmed by a comparison 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. The time scale over which the nonstationary component is decorrelated is also obtained. We estimate the global average ratio of total to stationary semidiurnal internal tide variance to be more than 10. In terms of the ratio of nonstationary to total semidiurnal internal tide variance, the semidiurnal nonstationary variance fraction (SNVF), this translates into a global average ratio of about 90%. The Argo in situ observations provide a valuable ground-truth for the geographical variability of the internal tides. The latter is key to predicting the magnitude and distribution of the mixing that ultimately results from the tides.