Making History

Jun 01, 2018
Planetary waves similar to those that control weather on Earth discovered on Sun

An international team of scientists, led by Laurent Gizon, co-principal investigator at the Centre for Space Science at NYU Abu Dhabi (NYUAD), have discovered planetary waves of vorticity - a measure of spin - on and inside the Sun similar to those that signifcantly influence weather on Earth.

Rossby waves are a natural phenomenon in the atmospheres and oceans of planets that form in response to the rotation of the planet. Like Earth, the Sun also rotates and should support Rossby waves, but their existence on the Sun was in debate, until now.

“There’s no doubt what we’re seeing are Rossby waves due to the measured, textbook relationship between frequency and wavelength,” said Gizon.

Solar Rossby waves are gigantic in size, Gizon explained, with wavelengths comparable to the solar radius. They are an essential component of the Sun’s internal dynamics because they contribute half of the Sun’s large-scale kinetic energy.

“That these waves are so big and are only seen in the equatorial regions of the Sun is completely unexpected,” he said.

Astrophysicists from NYUAD, the Max Planck Institute for Solar System Research, and Stanford University studied six years of space data, which revealed the Rossby waves moving in the direction opposite to the Sun’s rotation.

Rossby waves on the Sun are close relatives to those known to occur in the Earth’s atmosphere and oceans, Gizon said, but are extremely diffcult to detect on the Sun because they have very small flow amplitudes, around one meter per second.

“We don’t yet know what role Rossby waves play in the Sun, but know that they can’t be ignored in future studies,” said Katepalli R. Sreenivasan, principal investigator at NYUAD Center for Space Science.

“Their presence may help us understand solar convection at the largest spatial scales, which remains poorly understood. They are very hard to fnd because of low signal levels but this research team has used ingenious data processing techniques to discover their existence,” added Sreenivasan.
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