For the very first time, researchers have conducted nearly daily observations of the Sun’s global coronal magnetic field—an area of the Sun that has previously only been sporadically recorded. These new findings are shedding light on the mechanisms behind powerful solar storms, which can disrupt essential technologies and affect our daily lives here on Earth.
For the very first time, researchers have conducted nearly daily observations of the Sun’s global coronal magnetic field—an area of the Sun that has previously only been sporadically recorded. These new findings are shedding light on the mechanisms behind powerful solar storms, which can disrupt essential technologies and affect our daily lives here on Earth.
An analysis of the data gathered over a span of eight months using a tool known as the Upgraded Coronal Multi-channel Polarimeter (UCoMP) has just been published in Science.
The solar magnetic field is the main factor behind solar storms, which can threaten everything from power grids to communication systems, as well as satellite technologies like GPS. However, understanding how this magnetic field accumulates energy and subsequently erupts has been challenged by the difficulty of observing it in the solar corona, the Sun’s upper atmosphere.
Traditional polarimetric methods for measuring this magnetic region often necessitate large, costly equipment that has only been able to assess limited areas of the corona up until now. By combining coronal seismology with UCoMP data, researchers can create consistent and comprehensive representations of the magnetic field across the entire solar corona—the all-encompassing view observed during a solar eclipse.
“Global mapping of the coronal magnetic field has long been a significant gap in solar studies,” expressed Zihao Yang, the lead author who conducted this research while earning his PhD at Peking University, China, and currently a postdoctoral fellow at the National Science Foundation’s National Center for Atmospheric Research (NSF NCAR). “This research is essential in enhancing our comprehension of coronal magnetic fields, the sources of energy behind storms that affect Earth.”?
The international team consists of researchers from Northumbria University, UK; NSF NCAR; Peking University, China; and the University of Michigan. Funding for this research came from the National Natural Science Foundation of China and the National Key R&D Program of China, supported by the Newkirk graduate student fellowship awarded to Yang from NSF NCAR. The UCoMP instrument was developed with assistance from the U.S. National Science Foundation (NSF) and is currently operated by NSF NCAR at the Mauna Loa Solar Observatory.
Enhanced Instrument
While scientists have routinely measured the magnetic field of the Sun’s surface, known as the photosphere, capturing the much fainter coronal magnetic field has been a longstanding challenge. This has hindered a deeper understanding of the three-dimensional structure and evolution of magnetic fields in the corona, where solar storms form.
To investigate the three-dimensional coronal magnetic fields thoroughly, large telescopes like the NSF’s Daniel K. Inouye Solar Telescope (DKIST) are required. DKIST, the world’s largest solar telescope with a 4-meter-diameter aperture, has recently showcased its groundbreaking capacity to observe the coronal magnetic field in detail. However, DKIST cannot capture the entire Sun in a single view. The smaller UCoMP instrument is actually better suited for providing scientists with a global depiction of the coronal magnetic field, albeit at lower resolution and in a two-dimensional projection. Hence, observations from both instruments are highly complementary, giving a fuller perspective of the coronal magnetic field.
UCoMP mainly functions as a coronagraph, using a disk to block sunlight similar to an eclipse, making it easier to observe the corona. It also integrates a Stokes polarimeter, which captures additional spectral data such as coronal line intensity and Doppler velocity. Despite its smaller aperture (20 cm), UCoMP can take a wider view, enabling it to study the entire Sun most days.
Researchers employed a method called coronal seismology to track magnetohydrodynamic (MHD) transverse waves in the UCoMP data. These MHD waves provided critical information for constructing a two-dimensional map depicting the strength and direction of the coronal magnetic field.
A preceding study in 2020 utilized UCoMP’s predecessor along with the coronal seismology methodology to create the first global map of the coronal magnetic field. This was a vital advancement towards regular coronal magnetic field measurements. UCoMP’s advanced capabilities now allow for more detailed, routine assessments. During this study, the research team produced a total of 114 magnetic field maps from February to October 2022, averaging nearly one every other day.
“We are entering a groundbreaking era in solar physics research where routine measurements of the coronal magnetic field are possible,” noted Yang.
Enhancing Our Understanding
The recent observations have also yielded the inaugural measurements of the coronal magnetic field in the Sun’s polar regions. Direct observations of the Sun’s poles have been elusive, as the curvature near the poles keeps them out of our direct line of sight from Earth. Although the researchers did not directly observe the poles, they succeeded in measuring the magnetic emissions emanating from them for the first time, thanks in part to improved data quality from UCoMP and the Sun’s proximity to its solar maximum. The typically faint emissions from the polar regions have been notably stronger, facilitating the acquisition of coronal magnetic field results in these areas.
As a postdoctoral fellow at NSF NCAR, Yang will persist in his research on the Sun’s magnetic field; he aims to refine existing coronal models that rely on photospheric measurements. Since the current method utilized with UCoMP is limited to two dimensions, it still does not encompass the complete three-dimensional magnetic field. Yang and his colleagues aspire to merge their research with other techniques for a more comprehensive understanding of the entire vector of the magnetic field in the corona.
Understanding the third dimension of the magnetic field, oriented along the observer’s line of sight, is vital for comprehending how the corona is energized prior to solar eruptions. Ultimately, a combination of a large telescope and a complete global perspective is required to capture all the three-dimensional complexities behind solar phenomena like eruptions; this drives the motivation for developing the proposed Coronal Solar Magnetism Observatory (COSMO), a 1.5-meter-diameter solar refracting telescope that is currently undergoing final design studies.
“Given that coronal magnetism is the force that propels mass from the Sun across the solar system, we must observe it in 3D, covering the entire corona at once,” stated Sarah Gibson, COSMO Development Lead and co-author on the paper from NSF NCAR. “Yang’s research signifies a monumental advancement in our capability to comprehend how the Sun’s global coronal magnetic field evolves daily. This understanding is crucial for enhancing our predictions and preparations for solar storms, which increasingly pose threats to our technologically reliant society here on Earth.”
