June 18, 2013
Venus Express Observes Strenghtening Winds On Second Planet From Sun
Lee Rannals for redOrbit.com — Your Universe Online
The European Space Agency's (ESA) Venus Express spacecraft has revealed that the winds on the second planet from the Sun have been getting faster over the last six years.Venus holds a super-rotating atmosphere that is able to whip around the planet once every four Earth days. Scientists are able to monitor patterns in the long-term global wind speeds by tracking the movements of distinct features in the clouds of the planet.
Venus Express first arrived at the planet in 2006, when average cloud-top wind speeds were clocked at about 180 miles per hour. However, two studies have shown how these speeds are moving even faster now at 248 miles per hour.
“This is an enormous increase in the already high wind speeds known in the atmosphere. Such a large variation has never before been observed on Venus, and we do not yet understand why this occurred,” says Igor Khatuntsev from the Space Research Institute in Moscow and lead author of the paper published in the journal Icarus.
The team was able to determine the wind speeds by measuring cloud features in images moved between frames. They tracked over 45,000 features by hand and more than 350,000 features using a computer program. Another study published in the Journal of Geophysical Research, led by a team in Japan, used their own automated cloud tracking method.
Both studies have revealed regular variations linked to the local time of day and the altitude of the Sun above the horizon. One regular oscillation takes place every 4.8 days near the equator and is thought to be connected to atmospheric waves at lower altitudes.
“Our analysis of cloud motions at low latitudes in the southern hemisphere showed that over the six years of study the velocity of the winds changed by up to [42 mph] over a time scale of 255 Earth days — slightly longer than a year on Venus,” says Toru Kouyama from the Information Technology Research Institute in Ibaraki, Japan.
The teams also saw dramatic variations in the average wind speeds between consecutive orbits of Venus Express around the planet. Wind speeds at low altitudes varied, as clouds completed one journey around the planet in 3.9 days and on other occasions they took 5.3 days.
“Although there is clear evidence that the average global wind speeds have increased, further investigations are needed in order to explain what drives the atmospheric circulation patterns that are responsible, and to explain the changes seen in localized areas on shorter timescales,” says HÃ¥kan Svedhem, ESA´s Venus Express Project Scientist. “The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the Solar System. These results add more mystery to it, as Venus Express continues to surprise us with its ongoing observations of this dynamic, changing planet.”