NASA Study Reveals How Solar Flare Oscillations Affect Earth's Ionosphere

Two new NASA studies have shed light on the origins and the science behind solar flares. These explosions on the sun’s surface impact the entire solar system. They cause bursts of radiation to stream throughout the solar system and the effects are visible everywhere. NASA studies helped scientists observe how the pulses or oscillations in solar flares affect Earth’s atmosphere.

These studies were prompted after scientists from NASA first observed oscillations during a flare. The team from the first study spotted these oscillations by observing the sun’s total output of extreme ultraviolet energy, a type of light invisible to human eyes. This was conclusively proven Feb. 15, 2011, when an X-class solar flare — the most powerful kind of these intense bursts of radiation — was observed. Using various observation points, the team was able to track oscillations in the flare’s radiation.

“Any type of oscillation on the Sun can tell us a lot about the environment the oscillations are taking place in, or about the physical mechanism responsible for driving changes in emission,” said Ryan Milligan, lead author of the first study and solar physicist at NASA’s Goddard Space Flight Center and the University of Glasgow in Scotland, in a NASA release.

The study revealed pulses of ultraviolet light rippling through the sun’s chromosphere, its outer atmospheric layer. The team observed these extreme radiation pulses only during solar flares.

National Oceanic and Atmospheric Administration’s Geostationary Operation Environmental Satellite (GOES), which resides in near-Earth space, made the observations that detected the oscillations. The satellite studies the sun from Earth’s perspective by collecting X-ray and extreme ultraviolet irradiance data. According to the report, the satellite wasn’t initially designed to detect fine details like these oscillations but the findings came as a huge surprise for the team.

“Flares themselves are very localized, so for the oscillations to be detected above the background noise of the Sun’s regular emissions and show up in the irradiance data was very striking,” Milligan said in the release.

The first study proved these pulses were observed in extreme ultraviolet emission that originated lower in the chromosphere. This gave the team more information about how a flare’s energy travels through the sun’s atmosphere.

Readings from NASA’s Solar Dynamics Observatory (SDO) confirmed the findings and the paper was published in The Astrophysical Journal Letters on Oct. 9, 2017.

In the second study, scientists investigated a connection between solar flares and activity in Earth’s atmosphere. According to the release, the team discovered pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a C-class flare on July 24, 2016. C-class flares are of mid-to-low intensity and about 100 times weaker than X-flares.

The ionosphere is roughly 30 to 600 miles above Earth’s surface. This ever-changing region of the atmosphere reacts to changes from both Earth below and space above, making it a unique area for targeted study. The ionosphere swells up with incoming solar radiation, which ionizes atmospheric gases and relaxes at night as the charged particles gradually recombine. The team studied how the lowest layer of the ionosphere, called the D-region, responded to pulsations in a solar flare.

“This is the region of the ionosphere that affects high-frequency communications and navigation signals,” Laura Hayes, solar physicist at NASA Goddard and Trinity College in Dublin, Ireland, said in the release. “Signals travel through the D-region, and changes in the electron density affect whether the signal is absorbed, or degraded,” she added.

Very Low Frequency (VLF) radio signals helped study the flare’s effects on the D-region. These were standard communication signals transmitted from Maine and received in Ireland.

“The denser the ionosphere, the more likely these signals are to run into charged particles along their way from a signal transmitter to its receiver,” said the release.

By monitoring how the VLF signals propagate from one end to the other, scientists can map out changes in electron density.

The team used data from the VLF and the X-ray analysis of the extreme ultraviolet observations from the GOES and SDO observatories. The study showed the team the D-region’s electron density was pulsing in concert with X-ray pulses on the Sun. They published their results in the Journal of Geophysical Research on Oct. 17, 2017.

“X-rays impinge on the ionosphere and because the amount of X-ray radiation coming in is changing, the amount of ionization in the ionosphere changes too,” said Jack Ireland, a co-author on both studies and Goddard solar physicist. “We’ve seen X-ray oscillations before, but the oscillating ionosphere response hasn’t been detected in the past.”

Hayes and her colleagues used a model to determine just how much the electron density changed during the flare. They found the density increased as much as 100 times in just 20 minutes during the pulses. Scientists previously hadn’t estimated the extent of the impact these oscillating signals in a flare would have on the ionosphere. With further study, the team hopes to understand how the ionosphere responds to X-ray oscillations at different timescales and whether other solar flares induce this response.

“This is an exciting result, showing Earth’s atmosphere is more closely linked to solar X-ray variability than previously thought,” Hayes said. “Now we plan to further explore this dynamic relationship between the Sun and Earth’s atmosphere.”

The team feels these findings will also help us protect astronauts, satellites and man-made objects like the International Space Station, in the ionosphere, from harmful radiation.