Eclipse data illuminate mysteries of Sun's corona
Date:
June 5, 2020
Source:
University of Hawaii at Manoa
Summary:
Observations from total solar eclipses are used to measure the
shape of the Sun's magnetic field.
FULL STORY ========================================================================== Researchers at the University of Hawaiʻi Institute for Astronomy
(IfA) have been hard at work studying the solar corona, the outermost atmosphere of the sun that expands into interplanetary space. The
properties of the solar corona are a consequence of the Sun's complex
magnetic field, which is produced in the solar interior and extends
outward into space.
==========================================================================
IfA graduate student Benjamin Boe conducted a new study that used total
solar eclipse observations to measure the shape of the coronal magnetic
field with higher spatial resolution and over a larger area than ever
before. The results were published in the Astrophysical Journal on June 3.
The corona is most easily seen during a total solar eclipse -- when the
moon is directly between the Earth and Sun, blocking sunlight. Significant technological advances in recent decades have shifted a majority
of analysis to space-based observations at wavelengths of light not
accessible from the ground, or to large ground-based telescopes such as
the Daniel K. Inouye Solar Telescope on Maui. Despite these advances, some aspects of the corona can only be studied during total solar eclipses.
Boe was advised by UH Mānoa Astronomy Professor Shadia Habbal, a
coronal research expert. Habbal has led a group of eclipse chasers, the
Solar Wind Sherpas making scientific observations during solar eclipses
for more than 20 years. These observations have led to breakthroughs
in unveiling some of the secrets of the physical processes defining
the corona.
"The corona has been observed with total solar eclipses for well over a century, but never before had eclipse images been used to quantify its
magnetic field structure," explained Boe. "I knew it would be possible
to extract a lot more information by applying modern image processing techniques to solar eclipse data." Boe traced the pattern of the
distribution of magnetic field lines in the corona, using an automatic
tracing method applied to images of the corona taken during 14 eclipses
the past two decades. This data provided the chance to study changes in
the corona over two 11-year magnetic cycles of the Sun.
==========================================================================
Boe found that there were very fine-scale structures throughout the
corona.
Higher resolution images showed smaller-scale structures, implying that
the corona is even more structured than what was previously reported. To quantify these changes, Boe measured the magnetic field angle relative
to the Sun's surface.
During periods of minimum solar activity, the corona's field emanated
almost straight out of the Sun near the equator and poles, while it came
out at a variety of angles at mid-latitudes. During periods of maximum,
the coronal magnetic field was far less organized and more radial.
"We knew there would be changes over the solar cycle but we never
expected how extended and structured the coronal field would be,"
Boe explained. "Future models will have to explain these features in
order to fully understand the coronal magnetic field." These results
challenge the current assumptions used in coronal modeling, which often
assume that the coronal magnetic field is radial beyond 2.5 solar radii.
Instead, this work found that the coronal field was often non-radial to
at least 4 solar radii.
This work has further implications in other areas of solar research -
- including the formation of the solar wind, which impacts the Earth's
magnetic field and can have effects on the ground, such as power outages.
"These results are of particular interest for solar wind formation. It indicates that the leading ideas for how to model the formation of the
solar wind are not complete, and so our ability to predict and defend
against space weather can be improved," Boe said.
Boe is already planning to be part of his team's next eclipse
expeditions. The next one is slated for South America in December 2020.
========================================================================== Story Source: Materials provided by University_of_Hawaii_at_Manoa. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Benjamin Boe, Shadia Habbal, Miloslav Druckmu"ller. Coronal Magnetic
Field Topology from Total Solar Eclipse Observations. The
Astrophysical Journal, 2020; 895 (2): 123 DOI:
10.3847/1538-4357/ab8ae6 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2020/06/200605165915.htm
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