This data publication presents global mass variations that are induced by individual ocean partial tides. The data set was produced using the purely-hydrodynamical ocean tide model TiME in the framework of the DFG-project Nerograv\\ (https://www.lrg.tum.de/iapg/nerograv/) and can be used for gravimetric applications. The overall goal of this project is to improve the processing of gravimetric data sets (e.g. GRACE/GRACE-FO) by improving the understanding of sensor data, processing strategies, and background models. The here presented DOI can contribute to this goal as the here described tidally induced mass variations are an important part of the described background models.
As ocean tides are usually described as a superposition of so-called partial tides, the presented mass variations can be attributed to single partial tide frequencies and are thus represented for single partial tide frequencies. Here, not only the effect of direct gravitation exerted by the ocean water is included but also gravity variations due to the elastic yielding of the solid earth in response to water mass redistribution (the load tide) are allowed for.
The information describing the partial tides has been transformed to fully normalized Stokes Coefficients describing in-phase and quadrature fields as those are especially handy for gravimetric purposes. The next section describes the creation of the data in more detail.
An electric current is induced by the motion of electrical conducting seawater through the ambient geomagnetic field. The periodic oceanic tidal flow induces an electric current that emits periodical time-variable electromagnetic field signals. The radial component of the ocean tide induced magnetic field signals has successfully been extracted from magnetic field observations of the satellite missions CHAMP and Swarm. It is known that the amplitudes of these electromagnetic signals are modulated by, among other influences, variations of the electrical seawater conductivity distribution of the ocean. The electrical seawater conductivity in return depends on seawater temperature and salinity. In order to analyse the influence of variations in oceanic temperature and salinity, we modelled a complete set of monthly time slices of three dimensional global complex amplitudes of these electromagnetic field signals for the years 1990 to 2016. In order to analyse solely the influence of variations in the climate sensitive seawater temperature and salinity on the ocean tide induced magnetic field signals, the influences of the secular variation of the geomagnetic field and temporal variations in ocean tide transports have been neglected.The data set is a supplement to the article of Petereit et al. (2019). The detailed method used to create this data set can be found in the data and methods section of the article and the associated data description file.Several datasets and models have been combined in order to compute the necessary models for the electrical conductivity of the Earth's surface and the ocean tide induced electric currents. These are the two main components needed for the modelling of the electromagnetic field signals that are emitted by the ocean tide induced electric currents.The model for the electrical conductivity of the Earth is composed of three components: a 1-D mantle conductivity distribution (Grayver et al., 2017), the time constant sediment conductivity (Laske & Masters, 1997) and the time-varying ocean conductivity. Ocean conductivity values were derived from a dataset of monthly global seawater temperature and salinity distributions that were derived from in-situ observations (Cabanes et al., 2013) using the TEOS-10 Toolbox (IOC, SCOR & APSO, 2010) to solve the Gibbs-seawater equation.The ocean-tide induced electric current density was computed as the vector product of the oceanic seawater conductivity, the tidal transports of the TPXO8-atlas (Egbert & Erofeeva, 2002) and ambient geomagnetic field of the IGRF-12 (Thébault et al., 2015). While, the oceanic seawater conductivity was variable in time, the tidal transports and the field strength of the ambient geomagnetic field have been kept constant.