Observing Oscillations, Flares And Tornados On Sun

The Sunrise III mission offers a completely new view of the sun. First results have now been published

To the point

• First results published: Two years after the stratospheric flight of the Sunrise III solar observatory, the mission's first results are released today.
• Unprecedented data quality: Sunrise III has captured observational data of unprecedented quality from the Sun's visible surface and lower atmospheric layers.
• New insights: The data contain new information, such as on tornados in the solar plasma or on the processes occurring before and during a solar flare.
• Understanding the stormy sun: During the flight, the Sun displayed its full repertoire: quiet regions, eruptions, sunspots, and more.

For six and a half days in July 2024, the balloon-borne solar observatory Sunrise III kept its gaze fixed on the Sun. The stratospheric flight, which stretched from the northernmost tip of Sweden to Canada's Northwest Territories, yielded a treasure trove of data exceeding 200 terabytes. These observations are unique. They provide insights - unprecedented in detail - into a layer of the Sun approximately 2,000 kilometers thick and can continuously track its immense dynamics over several hours. This region encompasses the Sun's visible surface, the so-called photosphere, as well as the adjacent chromosphere above it. The complex interplay of hot plasma, fluctuating magnetic fields, and waves in this region is responsible, among other things, for our star's violent outbursts that hurl particles and radiation into space.

Understanding solar eruptions

During the flight, the Sun itself offered a comprehensive showcase of its capabilities: in addition to calm regions representing its moderate "normal" state, numerous signs of its temperament were also visible - such as sunspots, small and large solar flares, and regions of particularly high magnetic field strength.

A review article summarizing the mission's first scientific results was published today in the journal The Astrophysical Journal Letters and marks the start of a comprehensive focus issue, which is dedicated exclusively to the results of the Sunrise III mission. Individual studies based on Sunrise III data will gradually be added to the focus issue.

"The results already available are as diverse as the Sun itself," says MPS researcher Smitha Narayanamurthy, co-author of the review article and head of Science Working Group for Sunrise III. "They reveal new insights into the Sun's quiescent state and help us understand its volatile side", she adds. Here are some of the new findings, which will be published in the next days and weeks:

• Oscillations: Turbulent plasma flows inside the Sun generate waves that propagate throughout the entire star, all the way to its lower atmosphere. Acoustic waves with periods of about five minutes have so far been observed mainly in a layer about 100 to 200 kilometers above the Sun's visible surface. Sunrise III provides a significantly more detailed view. For the first time, researchers were able to track the propagation of these waves within the photosphere and chromosphere - a layer with a total thickness of 2,000 kilometers - and study the influence of the magnetic field present there.
• Solar flare: During the Sunrise III flight, a solar flare of the second-strongest category occurred on the Sun. Such a flare can cause moderate disruptions on Earth, for example in power grids or satellite systems. Sunrise III was able to track the flare in minute detail. In the chromosphere, elongated, brightly flashing structures appear during a solar flare. They form when magnetic field lines rearrange themselves there, thereby releasing energy. The Sunrise III data provides precise insights into the fine structure and changes in the magnetic field at these locations. This can help understand how small-scale processes in the chromosphere regulate the evolution of large solar flares.
• Solar tornados: The magnetic field lines extending from quiet regions of the Sun's surface into the chromosphere were previously considered to have a comparatively "orderly" structure. Sunrise III data, combined with computer simulations, now paint a different picture: finely twisted magnetic field lines are embedded within ordered magnetic strands. They control the flows of hot plasma in the chromosphere and are thus likely to be the sites of small "solar tornados."

So far, only a small portion of the Sunrise III data has been analyzed. "We're still just at the very beginning," says Sunrise III project manager Andreas Korpi-Lagg. "The data from the Sunrise III mission will keep us busy for many years to come - and will certainly hold a surprise or two," he adds.

Stratosphere offers unobstructed view

Primarily responsible for the high quality of the Sunrise III data - and thus for the mission's success - was the observatory's "workplace". In the stratosphere, about 35 kilometers above the Earth's surface, the observatory left most of the Earth's atmosphere behind. This layer of ever-moving air significantly limits the view of ground-based solar telescopes. Even with state-of-the-art techniques designed to compensate for atmospheric turbulence, only in extremely rare cases can the Sun be observed for more than a few minutes at a time without interruption and with consistently high image quality. Sunrise III, on the other hand, was able to conduct observation series lasting several hours. Even the onset of night caused little disruption: along Sunrise III's summer flight path near the Arctic Circle, the Sun sank very low for only a short time each day. Only during this period did the view through denser layers of the Earth's atmosphere impair Sunrise's observations.

Equally crucial was the observatory's scientific equipment: the telescope, with a primary mirror diameter of one meter, captured the sunlight; the three instruments SUSI (ultraviolet spectropolarimeter), TuMag (magnetograph), and SCIP (infrared spectropolarimeter) processed it further; and a sophisticated image stabilization system ensured sharp images. Equipped in this way, the observatory captured image sequences at intervals of about a quarter of a second, revealing structures as small as 50 kilometers in size - all from a distance of nearly 150 million kilometers. In addition, Sunrise III studied a broad wavelength range of the sunlight - from ultraviolet to infrared light - and could even distinguish between very closely adjacent wavelengths. Ultraviolet light from the Sun is inaccessible to ground-based telescopes as most of this radiation is absorbed by the Earth's ozone layer.

Background Information

The balloon-borne solar observatory Sunrise III is a mission of the Max Planck Institute for Solar System Research (MPS, Germany) and the Johns Hopkins Applied Physics Laboratory (APL, USA). Significant contributors to the mission are a Spanish consortium, the National Astronomical Observatory of Japan (NAOJ, Japan), and the Leibniz Institute for Solar Physics (KIS, Germany). The Spanish consortium is led by the Instituto de Astrofísica de Andalucía (IAA, Spain) and includes the Instituto Nacional de Técnica Aeroespacial (INTA), Universitat de València (UV), Universidad Politécnica de Madrid (UPM) and the Instituto de Astrofísica de Canarias (IAC). Other partners include NASA's Wallops Flight Facility Balloon Program Office (WFF-BPO) and the Swedish Space Corporation (SSC).

Sunrise III is supported by funding from the Max Planck Foundation, NASA under Grant #80NSSC18K0934 and #80NSSC24M0024 ("Heliophysics Low Cost Access to Space" program), and the ISAS/JAXA Small Mission-of-Opportunity program and JSPS KAKENHI JP18H05234. The Spanish contributions have been funded by the Spanish MCIN/AEI under projects RTI2018-096886-B-C5, and PID2021-125325OB-C5, and from "Center of Excellence Severo Ochoa" awards to IAA-CSIC (SEV-2017-0709, CEX2021-001131-S), all co-funded by European REDEF funds, "A way of making Europe".