Trinity-NASA research shows how solar variability affects Earth’s atmosphere

Posted on: 21 November 2017

The Earth’s atmosphere is closely coupled with the Sun. The Sun provides the heat and energy that drives our climate and weather patterns and ultimately provides the conditions for life here on Earth.

The Sun is also an active star and is continuously erupting with giant explosions — such as bursts of radiation called solar flares. These flares can have significant effects on the Earth’s atmosphere, so understanding this coupling between the Sun’s activity and the Earth’s ionized environment is important.

Led by PhD researcher in Trinity College Dublin’s Astrophysics Group, Laura Hayes, and her thesis advisor, Professor Peter Gallagher, a team of scientists from Trinity and NASA investigated a connection between solar flares and activity in Earth’s atmosphere.

The team discovered that pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a C-class flare that occurred in July last year.

C-class flares are of mid-to-low intensity, and about 100 times weaker than X-flares, while the ionosphere is an ever-changing region of the atmosphere that reacts to changes from both Earth below and space above. This region stretches from roughly 60 – 1,000 km above Earth’s surface, and swells in response to incoming solar radiation, which ionizes atmospheric gases, and relaxes at night as the charged particles gradually recombine.

Specifically, the team looked at how the lowest layer of the ionosphere, called the D-region, responded to pulsations in a solar flare.

Laura Hayes said: “This is the region of the ionosphere that affects high-frequency communications and navigation signals. Signals travel through the D-region, and changes in the electron density affect whether the signal is absorbed, or degraded.”

The scientists used data from very low frequency (VLF) radio signals to probe the flare’s effects on the D-region. These were standard communication signals transmitted from Maine in the US and received at Trinity’s observatory at Birr Castle, Co. Offaly, in Ireland.

The denser the ionosphere, the more likely these signals are to run into electrons along their way from a signal transmitter to its receiver. By monitoring how the VLF signals propagate from one end to the other, scientists can map out changes in electron density.

Pooling together the VLF data and X-ray and extreme ultraviolet observations from NOAA’s Geostationary Operational Environmental Satellite and NASA’s Solar Dynamics Observatory, the team found the D-region’s electron density was pulsing in concert with X-ray pulses on the Sun.

They published their results last month in the Journal of Geophysical Research.

Jack Ireland, a co-author and NASA Goddard solar physicist, said: “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. 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. In response to incoming radiation, they found the density increased as much as 100 times in just 20 minutes during the pulses — an exciting observation for the scientists who didn’t expect oscillating signals in a flare would have such a noticeable effect in 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.

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

The research was generously supported by an Irish Research Council Enterprise Partnership studentship between Trinity and Adnet Systems at NASA Goddard Space Flight Center. Director of the Irish Research Council, Dr Peter Brown, said: “On behalf of the Irish Research Council, I would like to congratulate Laura and Professor Gallagher on their work, which shows how closely linked the Earth’s ionosphere is to activity on the Sun.”

“We are delighted to have provided funding for Laura under the Enterprise Partnership Scheme. Postgraduate research programmes such as the Enterprise Partnership Scheme are vital to ensure that Ireland’s brightest talent is supported to develop research careers in exciting areas of scientific discovery.”

“The Irish Research Council is committed to providing opportunities for early-career researchers to collaborate with research projects across Europe and the US. It is through collaborations like these that we can further develop our understanding of the world in which we live and answer key questions about the Universe.”

The collaboration between Trinity and NASA is also supported by the US Trinity Alumni Fund.