Earth-like planetary waves discovered on Sun

Washington

Large-scale planetary waves that meander through the atmosphere high above Earth's surface have been found to also exist on the Sun, scientists say.

Just as the large-scale waves that form on Earth, known as Rossby waves, influence local weather patterns, the waves discovered on the Sun may be intimately tied to solar activity, including the formation of sunspots, active regions, and the eruption of solar flares.

"The discovery of magnetised Rossby waves on the Sun offers the tantalising possibility that we can predict space weather much further in advance," said Scott McIntosh, from the US National Centre for Atmospheric Research (NCAR).

On Earth, Rossby waves are associated with the path of the jet stream and the formation of low- and high-pressure systems, which in turn influence local weather events.

The waves form in rotating fluids — in the atmosphere and in the oceans. Since the Sun is also rotating, and because it is made largely of plasma that acts, in some ways, like a vast magnetised ocean, the existence of Rossby-like waves should not come as a surprise, said McIntosh.

Yet scientists have lacked the tools to distinguish this wave pattern until recently.

Unlike Earth, which is scrutinised at numerous angles by satellites in space, scientists historically have been able to study the Sun from only one viewpoint: as seen from the direction of Earth.

For a brief period, from 2011 to 2014, scientists had the unprecedented opportunity to see the Sun's entire atmosphere at once.

During that time, observations from NASA's Solar Dynamics Observatory (SDO), which sits between the Sun and the Earth, were supplemented by measurements from NASA's Solar TErrestrial RElations Observatory (STEREO) mission, which included two spacecraft orbiting the Sun.

The three observatories provided a 360-degree view of the Sun until contact was lost with one of the STEREO spacecraft.

Researchers mined the data collected during the window of full solar coverage to see if the large-scale wave patterns might emerge.

"By combining the data from all three satellites we can see the entire sun and that's important for studies like this because you want the measurements to all be at the same time," said Dean Pesnell, SDO project scientist at NASA's Goddard Space Flight Center in the US.

"They're pushing the boundary of how we use solar data to understand the interior of the sun and where the magnetic field of the Sun comes from," said Pesnell.

The discovery could link a range of solar phenomena that are also related to the Sun's magnetic field, including the formation of sunspots, their lifetimes, and the origin of the Sun's 11-year solar cycle.

"It's possible that it's all tied together, but we needed to have a global perspective to see that," McIntosh said.

The study was published in the journal Nature Astronomy. — PTI