15 January 2014

Venus’ cloud waves offer hints about what’s going on below

Image Credit: Wave trains on Venus. Credit: ESA/Venus Express/VMC/A. Piccialli et al., 2014.

Planetary scientists have known that the atmosphere on Venus acts more like a river or ocean than Earth’s atmosphere and a new study based on data from the European Space Agency (ESA) has found that the physical features of Venus’ surface play a role in the circulation of this atmosphere.

The new study focused on Venus’ lower atmosphere, which is capped by a dense cloud layer that behaves like the surface of a body of water. Waves and other phenomenon within this layer provide evidence of processes occurring below.

In November 2012, scientists published a study of a wave formation process in the atmosphere of Venus that was caused by the rise of lighter, warmer air from below, or the layer’s horizontal flow carrying it over an obstacle such as a tall peak. Using the Radio Science Experiment onboard the ESA’s Venus Express craft (VeRa), a team of scientists captured over 500 atmospheric profiles between the probe’s arrival at the planet in 2006 and July 2011.

The profile views of the upper atmosphere allowed scientists to examine occasional disturbances within the atmospheric temperature profiles, which took the form of ripples often hundreds of miles across, called gravity waves.

“We believe that these waves are at least partly associated with atmospheric flow over Ishtar Terra, an upland region which includes the highest mountains on Venus,” said Silvia Tellmann, of the University of Cologne in Germany. “We don’t yet fully understand how such topographic forcing can extend to high levels, but it seems likely to be one of the key processes for the generation of gravity waves at high northern latitudes on Venus. The waves may form when a stable air flow passes over the mountains.”

The new study, published in the journal Icarus, was able to confirm this earlier finding through data obtained with the Visible Monitoring Camera (VMC) on Venus Express.

Highly defined images of Venus’ northern hemisphere taken by the VMC showed four kinds of waves: long, medium, short and irregular. Waves extending more than a few hundred miles and with a separation of crests between 4.3 and 10.6 miles were categorized as long. Medium type waves extended over 62 miles (100 km) and with wavelengths of approximately 5 to 13 miles. Short waves extended to a few hundreds of miles, with wavelengths of 1.9 to 9.9 miles. The researchers said irregular wave fields were probably caused by wave interference.

Study author Arianna Piccialli noted that the high speed of the Venus Express as it orbits the planet prevented the team from obtaining more detailed images.

“By themselves, these constraints do not allow us to establish with absolute confidence the nature of these waves,” said Piccialli, a postdoctoral research fellow at the Laboratoire Atmospheres, Milieux, Observations Spatiales (LATMOS-UVSQ). “However, by comparing the morphology and properties of the wave features observed in VMC images to those seen by previous observations – such as the VeRa data – it is reasonable to assume that the waves studied here are gravity waves associated with air flow over the uplands of Ishtar Terra.”

“This is an exciting result because it strengthens the case that topography is likely to be a significant influence on the atmospheric circulation of Venus,” said Håkan Svedhem, ESA’s project scientist for Venus Express. “This influence has been predicted by models but never observed in such detail until now. Understanding the mechanisms of surface influence on atmospheric processes is crucial for understanding the maintenance of the remarkably rapid circulation of the atmosphere at Venus’ cloud tops.”

Now read: Newfound planet is Earth-mass but gassy


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