Astrophysics (index)about

atmospheric tide

(tide-type movement in the atmosphere)

An atmospheric tide is a movement of the atmosphere analogous to the tides of the Earth's oceans. In addition to tides due to gravity, it also includes significant tides due to thermal heating (thermal tide), e.g., from the Sun, which consists of flows away from the warmest spot and toward the coolest spot. In fact, the Earth's atmospheric tide is primarily thermal.

Atmospheric thermal tide has the interesting property that while "normal" tides tend to slow rotation (or rather to "drag" it until it matches the relative positions of the bodies if they orbit, i.e., tidal locking), an atmospheric tide affects rotation in the opposite direction, i.e., increase it, and it is possible that the opposing forces balance, i.e., the rotation remains stable. This is because the heated atmosphere under the influence of the host star is less dense, and as that is dragged a bit along with the planet's rotation, the more dense portion of the atmosphere in the other direction is pulled on by the host star. When the concept was first derived it was thought this might be the Earth's state. Some theories of Venus's unusual rotation attribute it to influence of its thermal tide.

It has been suggested that life, through its influence on atmosphere (e.g., supplying oxygen) affects the scale height of the atmosphere, thus could have an affect on thermal tide and the planet's rotation.


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