The path to solar weather forecasts

At times the sun ejects energetic material into space which can have consequences for space-based and even ground-based electronic technology. Researchers aim to understand this phenomenon and find ways to forecast it, including how ejected material evolves as it travels through the solar system. For the first time, researchers, including those from the University of Tokyo, made high-quality measurements of an evolving cloud of solar ejecta by using multiple space-based instruments which were not designed to do so, and observed the way the clouds reduce background cosmic-ray activity.

Solar storms, known as coronal mass ejections (CME), are surprisingly common. When detected in the vicinity of Earth, some satellites are even put into a safe, low-power mode until the storm passes in order to protect them. But as with more familiar terrestrial weather, it’s the events you can’t prepare for that necessarily cause the most damage. To aid in this regard, researchers are trying to figure out how CMEs evolve as they head away from their source, the sun. While some different approaches have been tried over time, a new method which pools the resources of several scientific satellites could lead to better space-weather forecasting.

“Understanding how huge clouds of solar material travel through space is essential for protecting satellites, astronauts, and even power grids on Earth,” said Ph.D. researcher Gaku Kinoshita from the Department of Earth and Planetary Science. “In our new paper, we show that the paths of these solar eruptions can be tracked using drops in cosmic rays, high-energy particles that constantly bombard the solar system, measured by spacecraft. By combining observations from several spacecraft at different locations, we were able to watch how one eruption changed shape and strength as it moved away from the sun, revealing new ways to improve space-weather forecasting.”

The researchers’ method works thanks to an effect known as Forbush decrease, which is the way a CME isn't perfectly transparent to cosmic rays coming from behind it. This is because the CME produces a strong magnetic field which can deflect charged particles like cosmic rays. By observing cosmic rays as a CME passes through a region, the team could interpret the physical makeup of the CME, and crucially, how it changes with time.

“In March 2022, three spacecraft — the European Space Agency (ESA)’s Solar Orbiter, ESA and Japan Aerospace Exploration Agency (JAXA)’s BepiColombo, and NASA’s Near Earth Spacecraft — happened to be ideally positioned to observe the same solar eruption from different locations in space. This rare alignment allowed us to compare how the event looked along different directions and distances from the sun,” said Kinoshita. “By combining cosmic-ray data with magnetic-field and solar-wind measurements, we could link changes in the particle signal directly to the physical structure of the eruption. One of the most important results of this work is showing that instruments never designed for science can still deliver valuable scientific data. We used a simple system-monitoring instrument onboard the BepiColombo spacecraft, originally meant only to keep the spacecraft healthy, and, through careful calibration, turned it into a detector of cosmic-ray decreases. Data that had long been ignored turned out to be too valuable to waste.”

While there are advanced instruments capable of monitoring CMEs directly, their operational periods are limited; whereas the above approach repurposes more general instruments that are always on, meaning they can continuously gather data. Researchers can also improve the quality of their data by combining data from multiple spacecraft — this is also important to build a 3D picture of the CMEs.

“Because the instruments used were never intended for scientific research, there was no existing framework to rely on. We had to evaluate an instrument’s behavior, calibrate it from scratch and develop new analysis methods ourselves before we could confidently use the data to study cosmic-ray decreases,” said Kinoshita. “With many spacecraft now operating between the sun and Earth, and more planned for the future, the chances of making routine multipoint observations are increasing. If we continue to combine data from multiple missions and use all available instruments, we can gain a far more complete picture of how solar ejections propagate through space.”

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Journal: Gaku Kinoshita, Beatriz Sanchez-Cano, Yoshizumi Miyoshi, Laura Rodríguez-García, Emilia Kilpua, Benoit Lavraud, Mathias Rojo, Marco Pinto, Yuki Harada, Go Murakami, Yoshifumi Saito, Shoichiro Yokota, Daniel Heyner, David Fischer, Nicolas Andre, and Kazuo Yoshioka, “Spatiotemporal Evolution of the 2022 March Interplanetary Coronal Mass Ejection Revealed by Multipoint Observations of Forbush Decreases”, The Astrophysical Journal, https://doi.org/10.3847/1538-4357/ae1834

Funding: This work was supported by JST SPRING (JPMJSP2108), STFC (ST/V004115/1 and ST/Y000439/1), the European Space Agency, the German Ministry for Economic Affairs and Climate Action / DLR (50QW2202), CNES, and the Institute for Space-Earth Environmental Research (ISEE), Nagoya University.

Useful links:

Graduate School of Frontier Sciences

https://www.k.u-tokyo.ac.jp/en/

Department of Complexity Science and Engineering

https://www.k.u-tokyo.ac.jp/complex/index_e.html

Graduate School of Science

https://www.s.u-tokyo.ac.jp/en/
 

Department of Earth and Planetary Science

https://www.eps.s.u-tokyo.ac.jp/en/

Research Contact:

Gaku Kinoshita

Department of Earth and Planetary Science, The University of Tokyo,

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JAPAN
g-kinoshita20686@g.ecc.u-tokyo.ac.jp

Press contact:
Mr. Rohan Mehra
Strategic Communications Group, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
press-releases.adm@gs.mail.u-tokyo.ac.jp

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