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Wayward field lines challenge solar radiation models

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This figure shows the average magnetic path of the particles with the thick white line. In the new model, the SEPs, the yellow dots, do not follow the average path, but travel along the wayward field lines meandering about the average path.

UCLan research team leads international study part-funded by NASA

Ground-breaking research by a team of international scientists,* led by the University of Central Lancashire (UCLan) and funded in part by the Science and Technology Facilities Council and NASA, has shed new light on the source of mysterious particles emanating from the Sun which can have knock-on effects here on Earth.

In addition to the constant emission of warmth and light, our Sun sends out occasional bursts of solar radiation that propel high-energy particles toward Earth. These solar energetic particles, or SEPs, can impact astronaut safety, satellites, and satellite navigation, radio communication and even flight schedules here on Earth. To fully understand the nature of these particles, scientists worldwide are looking at the SEP source: bursts of solar radiation.

However, scientists aren’t exactly sure which of the two main features of solar eruptions –narrow solar flares or wide coronal mass ejections – cause the SEPs during different bursts. So far researchers have tried to distinguish between the two possibilities by using observations, and computer models based on those observations, to map out where the particles could be found as they spread out and travel away from the Sun. The observations are made by particle detectors in spacecraft such as the NASA’s STEREO mission and the joint NASA and ESA mission SOHO.  

Our new model considers that magnetic pathways of the SEPs can wander – a result of turbulence in solar material as it travels away from the Sun.

Timo Laitinen, Post-Doctoral Research Associate at UCLan’s Jeremiah Horrocks Institute and lead researcher of the study said the data collected has revealed some unusual anomalies: “Sometimes these particles have appeared on the opposite side of the Sun to where the original eruption took place. What kind of explosion on the Sun could have caused this? This is the question we have all been asking ourselves.”

Now a new model, developed by the UCLan-led international team, shows how particles could travel to the back of the Sun no matter what type of event first propelled them. Previous models assumed the particles mainly follow the average of magnetic field lines in space on their way from the Sun to Earth, and slowly spread across the average over time. The average field line reaches from the Sun to the outer boundaries of our solar system, forming a distinct spiral because of the Sun’s rotation.

Timo continued: “Our new model considers that magnetic pathways of the SEPs can wander – a result of turbulence in solar material as it travels away from the Sun. With this added information, our models now show SEPs spiralling out much wider and farther than previously predicted – explaining how SEPs find their way to even the far side of the Sun.”

Thanks to the ability of several space missions, such as SOHO and STEREO, we are now able to fully understand how even narrow solar eruptions can fill the solar system with SEPs.

Timo concluded: “Thanks to the ability of several space missions, such as SOHO and STEREO, to simultaneously see SEPs from a single eruption at different locations in the solar system, we are now able to fully understand how even narrow solar eruptions can fill the solar system with SEPs.

“Our new model explains how the complexity of the outer solar atmosphere, the solar wind, can influence the SEP propagation. Future space missions such as ESA’s Solar Orbiter and NASA’s Solar Probe Plus, which go closer to the Sun, will help us further to analyse SEP propagation.

“The increased understanding of the SEP propagation will help us constrain the possible SEP formation mechanisms in different SEP eruptions. Together with the high-resolution images, and SEP data captured by spacecraft such as SOHO, STEREO and SDO our research will help us in the search of the SEP origins and their relation to the complex dynamics of the solar eruptions.”

Explanatory video here. (Video credit: NASA’s Goddard Space Flight Center/UCLan/Stanford/ULB/Joy Ng)

This study is summarized in a paper published in Astronomy and Astrophysics on June 6, 2016.

*The International research team engaged in this research are located at the following universities and institutes:

University of Central Lancashire, UK
Université Libre de Bruxelles, Belgium
University of Waikato, New Zealand
Stanford University, USA
The Met Office, UK

Photo credit: UCLan/SDO/Timo Laitinen

Chris Theobald | 17 October 2016