Becoming Better Solar Meteorologists, With Help From Some Monster Waves


This NASA Solar Dynamics Observatory view of the sun highlights the magnetic solar corona and a powerful solar flare erupting on the limb. NASA/SDO
This NASA Solar Dynamics Observatory view of the sun highlights the magnetic solar corona and a powerful solar flare erupting on the limb. NASA/SDO

The sun is an extreme cosmic environment where superheated gases broil and solar flares explode with the energy of millions of nuclear warheads. Recently, astronomers have discovered Rossby waves rippling through this hellish environment. These planetary waves were first identified in Earth's temperate atmosphere in 1939, and they're immense — think global scale rather than beach scale.

What's more, the discovery of Rossby waves in the solar corona eventually could help us forecast when the next big solar storm will bear down on us. The astronomers published their findings in Nature Astronomy on March 27, 2017.

Before we get into Rossby waves, here's a little backstory: The Earth and sun have a complex and often violent relationship. Our nearest star continuously pumps huge quantities of hot, ionized gas (called plasma) into space as the solar wind, and all the planets in the solar system feel the impacts of this steady stream. One beautiful effect is the interaction between solar wind particles and Earth's upper atmosphere – ions rain down at high latitudes, creating often spectacular aurorae, commonly known as the Northern and Southern Lights.

But explosive events, like solar flares and coronal mass ejections — basically huge bubbles of magnetized, superheated plasma — can have dramatic and often unpredictable impacts on our planet's magnetosphere (the global magnetic field) when it gets hit. These effects are collectively known as "space weather." At the extreme end of the scale, solar storms can wreak havoc — killing satellites, knocking out global communications and even overloading power grids.

Little wonder then that solar astronomers have been studying our sun in greater detail than ever before to predict what our sun might throw at us next and help us prepare for inclement space weather — just as a meteorologist would warn us of an incoming hurricane.

An Unprecedented Solar View

The detection of these waves on the sun didn't come as a surprise to solar physicist Scott McIntosh, who works at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, and is the study's lead author.

"It's a big rotating ball after all," he explains, referring to the fact that Rossby waves naturally form from the Coriolis force that acts on large rotating spheres of fluid, like Earth's atmosphere and oceans. They powerfully affect our climate and weather systems, and are associated with high-altitude jet streams and pressure regions. Rossby waves have even been spotted on Mars and Venus. On the sun, however, these waves aren't driven by atmospheric pressure systems but rather by magnetic activity – activity that is a driver of space weather.

Our view of the sun has been a decidedly Earth facing view for a long time but with the addition of STEREO we have for the first time, a whole sun view. This is critical if we are ever to truly understand the workings of the sun's magnetic fields, the drivers of space weather.
C. Alex Young, Solar Physicist, NASA's Goddard Space Flight Center

Until now, tracking waves of this scale on the sun has been very difficult, so McIntosh's team turned to observational data from the twin NASA Solar and Terrestrial Relations Observatory (STEREO) spacecraft and NASA's Solar Dynamics Observatory (SDO). That data gave McIntosh's team a 360-degree view around the sun to track the motions of coronal "brightpoints" from all sides simultaneously. Those brightpoints McIntosh's team focused on pepper the entire solar corona and are related to small magnetic regions in the sun's lower atmosphere.

When McIntosh and his team analyzed data from 2010 to 2013 from STEREO and SDO, making simultaneous measurements from all sides of the sun, vast wave-like pulsations were tracked in the sun's lower atmosphere over many months. Groups of brightpoints were moving westward faster than the underlying material; typical behavior for Rossby waves.

Space Weather Triggers

OK, so now that we're sure Rossby-like waves ripple around the sun, how can we use them?

"We know that big flares and CMEs cluster in longitude, latitude and time – their clustering is closely tied to surges in [magnetic] flux emergence – those surges are likely to do with the fact that the bulk of magnetism emerges where there already is strong magnetism," he adds. "So, if you know where the field is, and where it's most likely to erupt, you can get a good basis for ... where eruptions are most likely to occur."

The sun undergoes an approximate 22-year cycle, waxing and waning in magnetic activity, from "solar minimum" (when the number of sunspots and flaring activity is low) to "solar maximum" (when the sunspot number reaches its peak and flaring activity is high) and then back to solar minimum again. The brightpoints ripple through the corona during this cycle and are, interestingly, most abundant during solar minimum. As these features are intimately related to the internal magnetic dynamo of the sun and its natural cycle, this study links the internal magnetic activity with activity on the surface, potentially the key to refining space weather forecasting.

"Our view of the sun has been a decidedly Earth facing view for a long time but with the addition of STEREO we have for the first time, a whole sun view," solar physicist C. Alex Young, at NASA's Goddard Space Flight Center, tells HowStuffWorks.

"This is critical if we are ever to truly understand the workings of the sun's magnetic fields, the drivers of space weather."

McIntosh agrees, pointing out that continuous, 360-degree views of the sun are essential: "We NEED to do this, make the magnetic field measurements ALL the time to get ahead of the space weather 'problem.'"

Unfortunately, NASA lost contact with one of the STEREO spacecraft in 2014. Although limited communications with the probe was recently re-established, its useful life is likely over. Regardless, the confirmation of these monster waves meandering through the corona underscores the need for continuous monitoring of the sun if we are to truly become accurate solar meteorologists.