Thermal tides in neutrally stratified atmospheres: Revisiting the Earth's Precambrian rotational equilibrium

Vol. 684
10. Planets and planetary systems

Thermal tides in neutrally stratified atmospheres: Revisiting the Earth's Precambrian rotational equilibrium

by Mohammad Farhat, Pierre Auclair-Desrotour, Gwenaël Boué, Russell Deitrick, Jacques Laskar 2024, A&A, 684, A49

The climatic history of the Earth is scarcely constrained. A key element to model is the length of the day, which was likely shorter in the past than it is now. The variation in the length of the day is a consequence of the Earth's spin variation, resulting from different torques involving the Earth, the Sun, the Moon, the atmosphere, among others.

In this study, the authors revisit the evolution of the Earth's length of day since the Precambrian, challenging the hypothesis that the length of the day could have stabilized at 21 hours during that time. This study follows a previous one by the same team in which they revisited the evolution of the Earth-Moon system. Here, the authors use their previous results in addition to a new ab initio model of atmospheric tides to simulate the variation of the length of the day over the ages. This tidal model, which is suitable for rocky planets, describes a neutrally stratified atmosphere and considers dissipative processes with Newtonian cooling and diffusive processes in the planetary boundary layer.

The Lamb resonance in the atmosphere, a frequency overlap between atmospheric free oscillations and the semidiurnal forcing, was initially thought to be responsible for the stabilization of the length of the day during the Precambrian. In this study, the authors show that this resonance might have occurred but later in the Phanerozoic, and with insufficient strength to stabilize the length of the day.

In addition to its application to Earth, the authors propose a new model that could be applied to rocky exoplanets.