The wind speed on Venus exceeds 100 meters per second (360 km per hour) and surrounds the planet. This means that the atmosphere at cloud level on Venus rotates about 60 times faster than the planet itself, which is called “super rotation.” On Earth, the atmosphere rotates at almost the same speed as the surface.
Previous research has investigated the mechanisms of this superspin, but the details are not fully understood. The latest study by Lai and colleagues shows that the once-daily atmospheric tidal cycle created by the sun's heat is a much larger contributor to the planet's ultrafast winds than expected.
The daily warm-up rhythm is crucial
Rapid atmospheric rotation is often observed on rocky planets that are close to the star and rotate very slowly, such as Venus. While Venus takes 243 Earth days to completely rotate around itself, its atmosphere only takes 4 Earth days to orbit the planet.
To better understand this superrotation, researchers analyzed data collected between 2006 and 2022 by the European Space Agency's Venus Express satellites and the Japan Space Exploration Agency's Akatsuki satellites. Their focus was on thermal tides, which occur when sunlight warms the air on the dayside of the planet. Thermal tides on Venus are divided into two main components: diurnal tides, which occur on the planet once per day, and semidiurnal tides, which occur twice per day.
Previous studies suggested that semidiurnal tides play the major role in the superreturn. However, this new study also analyzed thermal tides, particularly in the southern hemisphere of Venus, and concluded that diurnal tides are the key component that transfers momentum to the upper parts of the clouds.
This suggests that daily tides play a significant role in maintaining extremely fast winds on Venus. Although researchers say more clarity is needed, the discovery sheds light on the meteorological mysteries of Venus and could also help study the atmospheres on other slowly rotating planets.
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