What is it about?
Since the time of Lord Kelvin, it has been believed that the yielding solid Earth due to the lunar (solar) gravitational force is an ellipsoid, in which solid Earth is slightly elongated along the Earth-Moon (Sun) line and shortened around the parts remote from the elongation. Nevertheless, the ellipsoid’s geometry such as major semi-axis’s length, minor semi-axis’s length, and flattening remains unresolved. The difficulty lies at two aspects: one is, as the Earth spins around its axis, no people may measure the long axis’s length and minor axis’s length of the ellipsoid. another is that tide workers conventionally use the expanded tidal potential equation and the given Earth model to compute the tidal displacement of a reference point, but this method cannot compute the minor axis’s length of the ellipsoid because the minor axis is not the only one (actually, there are countless minor axises in the ellipsoid that form a section, which is orthogonal to the long axis). In this study, we present a geometric model, in which both the ellipsoid's geometry and the tidal displacement of a reference point can be nicely resolved through a rotating ellipse with respect to the Moon (Sun). We have used Superconducting Gravity (SG) data to test this model and compare it with the current model recommended by the IERS (International Earth Rotation System) conventions (2010), we found the geometric model is far better than the current model.
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Why is it important?
The geometric model represents a significant advance in understanding solid Earth tide, and will greatly contribute to many application fields such as geodesy, geophysics, astronomy, and oceanography.
Perspectives
Newton in his principle described the planet’s motion as a consequence of the Sun’s gravitational force, but no people uses the gravitational force to directly compute the planet's motion. Instead, it is computed through the Kepler’s elliptical orbital model. The rotating ellipse model presented in this study may be similar to the Kepler’s elliptical orbital model, so, it is destined to succeed in resolving the ellipsoid's geometry and computing the tidal displacement. It is real, if one has read the current model recommended by the IERS conventions (2010) and the geometric model, he/she must conclude that the geometric model is the simplest and best.
Dr Yongfeng Yang
Bureau of Water Resources of Shandong Province
Read the Original
This page is a summary of: A rotational ellipsoid model for solid Earth tide with high precision, Scientific Reports, November 2024, Springer Science + Business Media,
DOI: 10.1038/s41598-024-79898-8.
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