The quiet Sun is much more active than we thought

Date:
August 4, 2020
Source:
Aalto University
Summary:
For a long time, researchers have believed that there is not
much of interest going on in the Sun during the passive period,
therefore not worth studying. Now this assumption is showed to be
false. This is the first time that astronomers are systematically
studying the phenomena of the solar minimum.



FULL STORY ========================================================================== Solar activity varies in 11-year cycles. As the activity cycle switches
to a new one, the Sun is usually very calm for several years.


==========================================================================
For a long time, researchers have believed that there is not much of
interest going on in the Sun during the passive period, therefore not
worth studying.

Now this assumption is showed to be false by Juha Kallunki, Merja
Tornikoski and Irene Bjo"rklund, researchers at Metsa"hovi Radio
Observatory, in their peer-reviewed research article published in Solar Physics. This is the first time that astronomers are systematically
studying the phenomena of the solar minimum.

Not all phenomena could be explained -- yet The researchers reached
their conclusion by examining the solar radio maps detected by the
Metsa"hovi Radio Observatory and comparing them with the data collected
by a satellite observing the Sun in the ultraviolet range. The solar
maps showed active areas, or radio brightenings, which can be observed
on the maps as hotter areas than the rest of the solar surface. According
to researchers, there are three explanations for radio brightenings.

First, some brightenings were observed in the polar areas on the solar
maps that could be identified as coronal holes. Particle flows, or solar
winds, ejected by coronal holes can cause auroras when they reach the
Earth's atmosphere. The corona is the outer atmosphere of the Sun.

Second, the researchers observed brightenings from which, based on
other observations, ejections of hot material from the surface of the
sun could be detected.



========================================================================== Third, radio brightenings were found in areas where, based on satellite observations, strong magnetic fields were detected.

Researchers also found radio brightenings in some areas where no
explanatory factor was found on the basis of satellite observations.

'The other sources used did not explain the cause of the brightening. We
don't know what causes those phenomena. We must continue our research', Kallunki says.

Additional observations and research are also needed to predict whether
the phenomena of the solar minimum indicate something about the next
active period, about its onset and intensity, for example. Each one of
the last four cycles has been weaker than the previous one. Researchers
do not know why the activity curves do not rise as high as during the
previous cycles.

'Solar activity cycles do not always last exactly 11 years, either',
explains Docent Merja Tornikoski.



==========================================================================
'A new activity period will not be identified until it is already
ongoing. In any case, these observations of the quiet phase we are
now analysing are clearly during a period when activity is at its
lowest. Now we are waiting for a new rise in activity.' Solar storms
can cause danger On the Earth, solar activity can be seen as auroras,
for example. Solar activity can even cause major damage, as solar storms
caused by solar flares can damage satellites, electricity networks and
radio frequency communications.

Research helps to prepare for such damage.

'In solar storms, it takes 2 to 3 days before the particles hit the
Earth. They reach satellites higher up in orbit much faster, which would
leave us even less time to prepare for damage', Kallunki points out.

Located in Kirkkonummi, Aalto University Metsa"hovi is the only
astronomical radio observatory and continuously operational astronomical observation station in Finland. Metsa"hovi is internationally known for
its unique, continuous datasets, including a solar monitoring programme spanning over 40 years that has collected data from scientifically very interesting high radio frequencies.

This is possible thanks to the exceptionally precise mirror surface of
the Metsa"hovi radio telescope.


========================================================================== Story Source: Materials provided by Aalto_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Juha Kallunki, Merja Tornikoski, Irene Bjo"rklund. Identifying 8
mm Radio
Brightenings During the Solar Activity Minimum. Solar Physics,
2020; 295 (7) DOI: 10.1007/s11207-020-01673-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200804111457.htm

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