A coronal lattice governs the formation of the solar wind

MADRID, November 25 (EUROPA PRESS) –

A dynamic, web-like network of elongated, interlocking plasma structures, governs the way the Sun launches the particles that make up the solar wind into space.

This is what a team of researchers led by the Max Planck Institute for Solar System Research (MPS) has captured for the first time using observational data from the US GOES satellites converted into computer simulations.

Together with data from other space probes and extensive computer simulations, a clear picture emerges: where the elongated structures of the coronal lattice interact, magnetic energy is discharged and the particles escape into space.

NOAA’s Geostationary Operational Environmental Satellites (GOES), which began launching in 1974, have traditionally dealt with weather forecasting. The three most recent ones currently in operation are additionally equipped with Sun-facing instruments for space weather forecasting. They can obtain images of ultraviolet radiation from the corona of our star.

An exploratory observing campaign to image the extended solar corona was carried out in August and September 2018. For more than a month, the GOES Solar Ultraviolet Imager (SUVI) not only looked directly at the Sun as it usually does, but it also captured images on both sides of the sun.

By combining the images from the different viewing angles, the instrument’s field of view could be significantly expanded and thus, for the first time, the entire middle corona, a layer of the solar atmosphere 350,000 kilometers above the visible surface of the Sun. , could be seen photographed in ultraviolet light.

The solar wind is one of the most far-reaching features of our star. The stream of charged particles that the Sun shoots into space travels to the edge of our Solar System, creating the heliosphere, a bubble of rarefied plasma that marks the Sun’s sphere of influence. Depending on its speed, the solar wind is divided into fast and slow components. The so-called fast solar wind, which reaches speeds of more than 500 kilometers per second, originates from inside coronal holes, regions that appear dark in coronal ultraviolet radiation. However, the regions of origin of the slow solar wind are less certain. But even particles from the slow solar wind They race through space at supersonic speeds of 300 to 500 kilometers per second.

This slower component of the solar wind still raises many questions. Coronal plasma hotter than a million degrees needs to escape from the Sun to form the slow solar wind. What mechanism is at work here? Furthermore, the slow solar wind is not homogeneous, but reveals, at least in part, a ray-like structure of clearly distinguishable streamers. Where and how do they originate? These are the questions addressed in the new study.

In the GOES data, you can see a region near the equator that aroused the researchers’ particular interest: two coronal holes, where the solar wind is moving away from the Sun unimpeded, very close to a region with a high magnetic field strength. . Interactions between systems like these are considered possible starting points for the slow solar wind. Above this region, the GOES data show elongated plasma structures in the central corona pointing radially outward. The author team refers to this phenomenon, which has now been directly imaged for the first time, as a coronal web. The network is in constant movement: its structures interact and regroup.

Researchers have long known that the solar plasma in the outer corona exhibits a similar architecture. For decades, the Large Angle and Spectrometric Coronagraph (LASCO) coronagraph aboard the SOHO spacecraft, which celebrated its 25th anniversary last year, has provided images of this region in visible light. Scientists interpret the jet streams in the outer corona as the structure of the slow solar wind that begins its journey into space there. As the new study now impressively shows, this structure is already prevalent in the midcrown.

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 in the sun’s corona. In this study, the team used an advanced magnetohydrodynamic (MHD) model to simulate the magnetic field and plasma state of the corona during this time period. “This helped us connect the fascinating dynamics we observed in the central corona with prevailing theories about the formation of the solar wind,” Dr. Cooper Downs of Predictive Science Inc., who performed the computer simulations, said in a statement.

As the calculations show, the coronal lattice structures follow the magnetic field lines. “Our analysis suggests that the architecture of the magnetic field in the central corona is imprinted in the slow solar wind and plays an important role in accelerating particles into space,” he said. it’s a statement Pradeep Chitta, a scientist at MPS and lead author of the new study. According to the team’s new results, the hot solar plasma in the central corona flows along the open magnetic field lines of the coronal lattice. Where the field lines cross and interact, energy is released.

There is much to suggest that researchers are looking at a fundamental phenomenon. “During periods of high solar activity, coronal holes often occur near the equator in the vicinity of areas of high magnetic field strength,” Chitta said. “Therefore, it is unlikely that the coronal web we observed is an isolated case,” adds.