“Tidal waves” power super-fast rotation of Venus’ atmosphere

An international team of scientists led by Takeshi Horinouchi of Hokkaido University suggests that a atmospheric equivalent of tidal waves may be responsible for the super-rotation of the atmosphere of Venus. Based on data returned by JAXA’s Akatsuki Venus orbiter, the new model shows how the Venusian atmosphere acts like a giant heat engine.

With a super-dense atmosphere hot enough to melt lead and where it rains sulfuric acid, Venus is a planet of surprises. One such surprise uncovered in the 1960s is that while Venus orbits the Sun once every 225 days, one Venusian day is 243 Earth days long. In other words, the Venusian day is longer than a Venusian year.

However, odd though that is, the atmosphere of Venus exhibits super-rotation. That is, the atmosphere rotates many times faster than the planet, and, at very high altitudes, it rotates once every four Earth days. The question is, what causes this?

Horinouchi’s team, which includes colleagues from JAXA and the Institute of Space and Astronautical Science (ISAS), developed a new method of analyzing images from the ultraviolet and infrared camera aboard the Akatsuki orbiter to measure temperature differences between low and high latitudes.

They found that the circulation of the Venusian atmosphere indicated that there was a mechanism powered by the Sun that reinforces and maintains the super-rotation instead of dispersing it.

Put simply, the atmosphere on the daylight side of Venus heats up and rushes toward the cooler nightside. This takes the form of something akin to a jet stream near the equator at high altitudes. A similar effect could, potentially, happen on Earth, except our planet rotates faster and it has oceans that break up simple circulation patterns.

Something like this dispersion should happen on Venus, too, for other reasons, but the Horinouchi team says that in the higher northern and southern latitudes of Venus, the air circulates in opposite directions toward the poles due to the same heating and cooling. This tidal wave-like circulation pushes the super-rotating air in the lower latitudes together and upwards, reinforcing the air stream. This transports heat around the planet and helps to power the north/south circulation cells.

“Our study could help better understand atmospheric systems on tidally-locked exo-planets whose one side always facing the central stars, which is similar to Venus having a very long solar day,” says Horinouchi.

The study was published in Science.

Source: Hokkaido University

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