Prof Norman Murray sheds light on why the day is 24 hrs long

Read the full A&S News Article by Chris Sasaki here, excerpt below

A team of astrophysicists, including CITA Prof Norman Murray, has revealed how the slow and steady lengthening of Earth’s day caused by the tidal pull of the moon was halted for over a billion years.

They show that from approximately two billion years ago until 600 million years ago, an atmospheric tide driven by the sun countered the effect of the moon, keeping Earth’s rotational rate steady and the length of day at a constant 19.5 hours.

Without this billion-year pause in the slowing of our planet’s rotation, our current 24-hour day would stretch to over 60 hours.

Drawing on geological evidence and using atmospheric research tools, the scientists show that the tidal stalemate between the sun and moon resulted from the incidental but enormously consequential link between the atmosphere’s temperature and Earth’s rotational rate.

The study describing the result, ‘Why the day is 24 hours long; the history of Earth’s atmospheric thermal tide, composition, and mean temperature,’ was published in the journal Science Advances.

The paper’s authors include Norman Murray, a theoretical astrophysicist with the Faculty of Arts & Science’s Canadian Institute for Theoretical Astrophysics (CITA); graduate student Hanbo Wu, CITA and Department of Physics; Kristen Menou, David A. Dunlap Department of Astronomy & Astrophysics and Department of Physical & Environmental Sciences, University of Toronto Scarborough; Jeremy Laconte, Laboratoire d’astrophysique de Bordeauxand and a former CITA postdoctoral fellow; and Christopher Lee, Department of Physics.

“It’s like pushing a child on a swing,” says Murray. “If your push and the period of the swing are out of sync, it’s not going to go very high. But, if they’re in sync and you’re pushing just as the swing stops at one end of its travel, the push will add to the momentum of the swing and it will go further and higher. That’s what happened with the atmospheric resonance and tide.”

Along with geological evidence, Murray and his colleagues achieved their result using global atmospheric circulation models (GCMs) to predict the atmosphere’s temperature during this period. The GCMs are the same models used by climatologists to study global warming. According to Murray, the fact they worked so well in the team’s research is a timely lesson.

“I’ve talked to people who are climate change skeptics who don’t believe in the global circulation models that are telling us we’re in a climate crisis,” says Murray. “And I tell them: We used these global circulation models in our research, and they got it right. They work.”

Despite its remoteness in geological history, the result adds additional perspective to the climate crisis. Because the atmospheric resonance changes with temperature, Murray points out that our current warming atmosphere could have consequences in this tidal imbalance.

“As we increase Earth’s temperature with global warming, we’re also making the resonant frequency move higher — we’re moving our atmosphere farther away from resonance. As a result, there’s less torque from the sun and therefore, the length the day is going to get longer, sooner than it would otherwise.”

Check out the paper in Science Advances here