Home Science Direct observations of a complex coronal web uncover an important clue as to what mechanism drives solar wind

Direct observations of a complex coronal web uncover an important clue as to what mechanism drives solar wind

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Atmosphere of the Sun: A computer simulation of the magnetic field structure in the coronal core on August 17, 2018. The ray-like features in this snapshot are the underlying magnetic structure of the observed coronal web. In the central corona, the predominantly closed field lines close to the Sun are replaced by the predominantly open field lines of the outer corona. Credit: Nature Astronomy, Chitta et al.

Using observations from the US weather satellite GOES, a research team led by Germany’s Max Planck Institute for the Solar System (MPS) has taken an important step towards unlocking one of the sun’s most enduring secrets. rice field. Particles that make up the solar wind into space? This data provides a unique view of a key region of the solar corona that has been largely inaccessible to researchers so far.

For the first time, the team captured a dynamic web-like network of elongated, interwoven plasma structures.together with other data space probe And with large-scale computer simulations, a clear picture emerges. Where elongated coronal web structures interact, magnetic energy is released and particles escape into space.

The National Oceanic and Atmospheric Administration’s (NOAA) Geostationary Operational Environment Satellites (GOES) have traditionally been concerned with things other than the Sun. Since 1974, the system has been orbiting the earth at an altitude of about 36,000 kilometers, continuously providing earth-related data such as weather and storm forecasts.

Over the years, the original configuration has expanded to include new satellites. The latest three of his units currently in operation are additionally equipped with solar-viewing instruments for space weather forecasting.They can image ultraviolet radiation from our star corona.

An exploratory observational campaign to image expansion solar corona Conducted in August and September 2018. For more than a month, GOES’ Solar Ultraviolet Imager (SUVI) not only looked directly at the Sun as usual, but also captured images on both sides of the Sun.

Dr. Dan Seaton of SwRI, who served as SUVI’s lead scientist during the observation campaign, said: “I didn’t even know if it would work, but I knew it would lead to important discoveries.”

By combining images from different viewing angles, the instrument’s field of view can be greatly expanded, and thus for the first time, the entire intermediate corona, the layer of the solar atmosphere 350,000 kilometers above the visible plane of the Sun, can be visualized. is ready. Taken in UV.

Other spacecraft that study the Sun and collect data from the corona, such as NASA’s Solar Dynamics Observatory (SDO) and NASA and ESA’s Solar and Heliospheric Observatory (SOHO), examine deeper or higher layers. . “There was a blind spot in solar studies during the mid-corona period. GOES data now offer a significant improvement,” said Dr. Pradeep Chitta of MPS, lead author of the new study. In the mid-corona, researchers suspect processes that drive and regulate solar energy. Wind.

travel through space at supersonic speed

The solar wind is one of the most pervasive features of our star. The stream of charged particles that the Sun casts into space travels all the way to the edge of the Solar System, creating the heliosphere, a tenuous bubble of plasma that marks the Sun’s sphere of influence. The solar wind can be divided into fast and slow components according to its speed.

The so-called fast solar wind, which reaches velocities of more than 500 kilometers per second, originates inside the coronal hole, the ultraviolet-dark region of the corona. However, the origin of the slow solar wind is less certain. But even the slow solar wind particles supersonic 300-500 kilometers per second.

This slow component of the solar wind still raises many questions. The hot coronal plasma, over one million degrees Celsius, must escape the Sun to form the slow solar wind. What mechanisms are at work here? Moreover, the slow solar wind is not uniform, but at least partially exhibits a ray-like structure of distinct streamers. Where and how do they occur? These are the questions addressed in the new study.

Capturing the Dynamic Corona Web

Origin of the Solar Wind: This is a mosaic of images taken on August 17, 2018 by the GOES instrument SUVI and the SOHO Coronagraph LASCO. Outside the white-marked circle, LASCO’s field of view shows the slow flow of the solar wind. These are seamlessly connected to the structure of the coronal web network in the coronal center seen inside the circle marked with white. Where the long filaments of the coronal web interact, the slow solar wind begins its journey into space.Credits: Nature Astronomy, Chitta et al. / Goes/Suvi/ Soho/Lusco

In the GOES data, we can see regions near the equator that have aroused special interest for researchers. Two coronal holes leave the solar wind unimpeded from the Sun and are close to regions of high magnetic field strength. Interactions between such systems are thought to be potential starting points for slow solar winds.

Above this region, the GOES data show an elongated plasma structure with a central corona pointing radially outwards. The authors’ team calls this phenomenon, which has been directly imaged for the first time, the Coronal Web. The web is always in motion. Its structure interacts and rearranges.

Researchers have long known that the solar plasma in the outer corona exhibits a similar structure. For decades, the Large Angle and Spectrometric Coronagraph (LASCO) aboard his SOHO spacecraft, which celebrated its 25th anniversary last year, has provided images of the region in visible light. Scientists interpret the jet-like flow of the outer corona as a slow solar wind structure from which it begins its journey into space. This structure is already widespread in the mid-corona period, as a new study impressively shows.

Influence of solar magnetic field

To better understand this phenomenon, researchers also analyzed data from other spacecraft. Her STEREO-A spacecraft, which has preceded Earth in orbit around the Sun since 2006, provided a side view.

Using modern computational techniques incorporating remote sensing observations of the Sun, researchers can use supercomputers to build realistic 3D models of the elusive magnetic field of the solar corona. In this study, the team used advanced magnetohydrodynamic (MHD) models to simulate the coronal magnetic field and plasma conditions during this period.

“This helped us connect the fascinating dynamics observed during the mid-corona period to a general theory of the formation of the solar wind,” said Dr. Cooper Downs of Predictive Science Inc., who performed the computer simulations. increase.

As calculations show, the structure of the coronal web follows the magnetic field lines. “Our analysis suggests that the structure of the central coronal magnetic field is imprinted on the slow corona. Solar wind According to the team’s new results, hot solar plasma in the coronal core flows along the open magnetic field lines of the coronal web. Where magnetic field lines cross and interact, energy is released.

There are many things that suggest that researchers are working on a fundamental phenomenon. “During periods of high solar activity, coronal holes often form in close proximity to regions of high magnetic field strength near the equator,” says Chitta. “Thus, the corona network we observed is unlikely to be an isolated case,” he adds.

The team hopes to get even more detailed insights from future solar missions. Some of them, such as ESA’s Proba-3 mission planned for 2024, are equipped with instruments that specifically target the intermediate corona. increase.together observation data From currently operating probes such as NASA’s Parker Solar Probe and ESA’s Solar Orbiter, which leave the Earth-Sun line, this will allow us to better understand the three-dimensional structure of the coronal web.

This research natural astronomy.

For more information:
LP Chitta et al, Direct Observation of Complex Coronal Web Driving Highly Structured, Slow Solar Wind, natural astronomy (2022). DOI: 10.1038/s41550-022-01834-5

provided by
Max Planck Society

Quote: Direct observation of the complex coronal web reveals important clues about the mechanism driving the solar wind (25 November 2022). uncover-important.html

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