Scientists only discovered the Giant Dark Cloud recently although the structure has existed for at least 30 years.
Planetary scientists have figured out the nature of the long-lived structure in the clouds of Venus, called the Giant Dark Cloud. It turned out that the atmospheric front associated with the Kelvin wave, which is also observed in the Earth’s atmosphere, is responsible for the change in the properties and structure of clouds.
Everything you need to know about the Giant Dark Cloud of Venus and all recent discoveries
The Giant Dark Cloud
For the first time, the Giant Dark Cloud, which is a large area near the planet’s equator, where the transparency of Venus’s clouds changes dramatically, was noticed in the near-infrared using the cameras of the Japanese interplanetary station Akatsuki, which has been operating in near-Venusian orbit since 2015. Later it turned out that this structure has a circulation period of 4.9 days and has existed for at least thirty years.
A group of planetary scientists led by Kevin McGouldrick from the Laboratory of Atmospheric and Space Physics at the University of Colorado in Boulder decided to understand the nature of this structure in the atmosphere of Venus.
Scientists focused their analysis on the data of observations of the planet obtained by the VIRTIS instrument, which was aboard the Venus orbital station Venus Express, as well as the data of the Akatsuki spacecraft.
Properties of clouds
The researchers found that changes in the structure and properties of clouds in the Giant Dark Cloud refer to heights below 50 kilometers and 50-57 kilometers, which corresponds to low and middle cloud layers.
The scientists concluded that they were dealing with an atmospheric front associated with a supercritical nonlinear Kelvin wave. On Earth, the source of equatorial Kelvin waves is the intensification of convection processes over the Pacific Ocean.
The density of the air mixture
In the case of Venus, a local maximum of the density of the air mixture appears at the leading edge of the moving front of the Kelvin wave, which triggers narrow downdrafts. They quickly reach lower altitudes, where increased air density stops them and results in wider and weaker updrafts.
Scientists note that they will continue to study this curious structure in the atmosphere of Venus, observing both ground-based telescopes such as IRTF and orbiters such as Akatsuki and the future EnVision and VERITAS.
Studying Venus in 2021
Low-frequency radio emissions
Earlier this year, scientists confirmed that The Parker solar probe was able to detect low-frequency radio emission from the nighttime ionosphere of Venus during the third approach to the planet. The data obtained by the probe helped planetary scientists to confirm the variability of the ionospheric density during the 11-year solar cycle.
Double Venus flyby
Then, last month, ESA’s spacecraft BepiColombo and the Solar Orbiter made a double flyby past Venus almost simultaneously. Scientific instruments aboard both probes monitored ions in the Venusian magnetosphere and ionosphere and also obtained clear spectra of the atmosphere of Venus – the last time such detailed observations were conducted by the Venera 15 station in the early 1980s. In addition, the onboard cameras on the spacecraft received a number of images of the planet.
The sound of Venus’ magnetosphere
The BepiColombo team also turned into sound the data collected by the magnetometers of the MPO probe, which demonstrate the interaction of the solar wind with the planet’s magnetosphere, in particular, the moment the spacecraft hits the head shock wave region, where the magnetosphere meets the solar wind, is clearly distinguishable. Intense noise indicates a region of a turbulent magnetosheath ahead of the bow shock.
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• Bartels, M. (2021, August 27). Scientists puzzling out secrets of Venus’ 30-YEAR-OLD ‘giant DARK CLOUD’. Space.com.
• McGouldrick, K., Peralta, J., Barstow, J. K., & Tsang, C. C. C. (2021, August 6). Using VIRTIS on Venus Express to Constrain the Properties of the Giant Dark Cloud Observed in Images of Venus by IR2 on Akatsuki. The Planetary Science Journal.