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Astronomers unveil Solar Corona’s magnetic field

The corona has been most easily seen during a total solar eclipse, it is when the moon is directly between the Earth and Sun which blocks the bright surface of the Sun.

Jun 5, 2020 15:25 IST
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The researchers at the University of Hawaii Institute of Technology (IFA) have been studying the solar corona. It is an outermost atmosphere of the sun that expands into interplanetary space.

A new study has been published in Astrophysical Journal on June 3 by IFA graduate student Benjamin Boe that used total solar eclipse observations to measure the shape of the coronal magnetic field along with a higher spatial resolution and over a large area than never before.

The corona has been most easily seen during a total solar eclipse, it is when the moon is directly between the Earth and Sun which blocks the bright surface of the Sun.

What is Solar Corona?

It is an outermost atmosphere of the sun that expands into interplanetary space. This stream of charged particles that have been radiating from the surface of the Sun is called the Solar wind and it expands to fill the entire Solar system.

The properties of the Solar corona have been the consequence of the Sun’s complex magnetic field that is produced in the solar exterior and then extends outwards.

The significant technological advances in the recent decades have shifted much of the focus to the space-based observations at wavelengths of light that has not been accessible from the ground or to the large ground-based telescopes such as the Daniel K. Inouye Solar Telescope on Maui.

But despite these advances, some of the aspects of corona can only be studied during the total solar eclipses.

Study of Solar Corona:

As some aspects of the corona can only be observed during the total solar eclipses, Coronal research expert and Boe’s advisor, Shadia Habbal led a group of eclipse chasers to make scientific observations during Solar eclipses for over 20 years. They are known as ‘Solar Wind Sherpas’ and they traveled the world chasing total solar eclipses and transporting sensitive scientific instruments on helicopters, planes, cars and even horses to reach the optimal locations.

These observations of Solar eclipses led to breakthroughs in unveiling some of the secrets of the physical processes that define Corona. As per the IFA graduate student, Benjamin Boe, the Corona has been observed with total solar eclipses for well over the century but had never before the eclipse images had been used to quantify its magnetic field structure. He added that it would be possible to extract a lot more information by applying modern-day image processing techniques to solar eclipse data.

How the study for the magnetic field in Solar Corona was done?

Benjamin Boe traced the pattern of the distribution of magnetic field lines in the corona with the use of an automatic tracing method applied to the images of the corona that were taken during 14 eclipses across the past two decades. This data provided an opportunity to study the changes in the corona over the two 11 year magnetic cycles of the sun.

Boe also found that the pattern of the coronal magnetic field lines has been highly structured, with structures that were seen at size scales down to the resolution limit of the camera used for the observations.

He also observed the pattern changing with time. To quantify the observed changes, Boe measured the magnetic field angle relative to the sun’s surface.

What was found was that during the minimum solar activity, the corona’s field emanated almost straight out of the sun near the poles and the equator, while it came out at a variety of angles at mid-latitudes.

While during the maximum solar activity, the coronal magnetic field was far less organised and was more radial.

Boe mentioned that the researchers were aware that there will be changes over the solar cycle but it was never expected that how structured and extended the coronal field would be. Future models will be able to explain these features in order to completely understand the coronal magnetic field.

Result of the study:

The results have challenged the current assumptions that were used in coronal modeling. It often assumed that the coronal magnetic field is radial beyond 2.5 solar radii. But this work found that the coronal field was often non-radial to at least 4 solar radii.

This observation will also have further implications in other areas of solar research, which also includes the formation of the solar wind that impacts the Earth’s magnetic field and can also have effects on the grounds such as power outages.

Benjamin Boe mentions that the results are of particular interest for the solar wind formation. It shows that the leading ideas of how to model the formation of the solar wind are not complete and so our ability to defend and predict against space weather can be improved.

The team has already been planning their next eclipse expeditions. The next one is slated for South America in December 2020.

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