First Found on Earth, Planetary Waves, Are Discovered on Sun

Dynamics of the troposphere-stratosphere-mesosphere exchanges including contribution of gravity waves and planetary waves.

Credit: ARISE Project

 

The study will be published March 27 in the journal Nature Astronomy. Co-authors are William Cramer of Yale University, Manuel Pichardo Marcano of Texas Tech University, and Robert Leamon of the University of Maryland, College Park.

The research was funded by the National Science Foundation (NSF), which is NCAR’s sponsor, and by NASA.

An unprecedented view of the Sun

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. Because the Sun is also rotating, and because it’s made largely of plasma that acts, in some ways, like a vast magnetized ocean, the existence of Rossby-like waves should not come as a surprise, said McIntosh, who directs NCAR’s High Altitude Observatory.

And yet scientists have lacked the tools to distinguish this wave pattern until recently. Unlike Earth, which is scrutinized 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.

But 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. Collectively, the three observatories provided a 360-degree view of the Sun until contact was lost with one of the STEREO spacecraft in 2014. McIntosh and his co-authors 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 Greenbelt, Maryland. “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.”

Finding waves in the data

The team used images taken by instruments on SDO and STEREO to identify and track coronal bright points. These small bright features dot the entire face of the Sun and have been used to track motions deeper in the solar atmosphere.

The jet stream that circles Earth’s north pole travels west to east. But when the jet stream interacts with a Rossby wave, as shown here, the winds can wander far north and south, bringing frigid air to normally mild southern states.  

David Hosansky, University Corporation for Atmospheric Research