Scientists explain mysterious finger-like features in solar flares


Date:
January 27, 2022
Source:
Harvard-Smithsonian Center for Astrophysics
Summary:
Astronomers have presented a new explanation for the mysterious
downward- moving dark voids seen in some solar flares.



FULL STORY ==========================================================================
In January 1999, scientists observed mysterious motions within a solar
flare.


========================================================================== Unlike typical flares that showed bright energy erupting outwards from
the Sun, this solar flare also displayed a downward flow of motion, as if material was falling back towards the Sun. Described as "downward-moving
dark voids," astronomers wondered what exactly they were seeing.

Now, in a study published today in Nature Astronomy, astronomers at
the Center for Astrophysics | Harvard & Smithsonian (CfA) offer a new explanation for the poorly understood downflows, now referred to as supra-arcade downflows (SADs) by the scientific community.

"We wanted to know how these structures occur," says lead author and
CfA astronomer Chengcai Shen, who describes the structures as "dark
finger-like features." "What's driving them and are they truly tied
to magnetic reconnection?" Scientists have assumed that SADs are tied
to magnetic reconnection since their discovery in the 90s. The process
occurs when magnetic fields break, releasing fast moving and extremely energetic radiation, and then reform.

"On the Sun, what happens is you have a lot of magnetic fields that are pointing in all different directions. Eventually the magnetic fields
are pushed together to the point where they reconfigure and release a
lot of energy in the form of a solar flare," says study co-author and
CfA astronomer Kathy Reeves.



========================================================================== Reeves adds, "It's like stretching out a rubber band and snipping it in
the middle. It's stressed and stretched thin, so it's going to snap back." Scientists assumed the dark downflows were signs of the broken magnetic
fields "snapping back" to the Sun after a solar flare eruption.

But there was a catch.

Most of the downflows observed by scientists are "puzzlingly slow,"
says co- author Bin Chen, an astronomer at the New Jersey Institute
of Technology.

Shen explains, "This is not predicted by classic reconnection models,
which show the downflows should be much quicker. It's a conflict that
requires some other explanation." To find out what was happening,
the team analyzed downflow images captured by the Atmospheric Imaging
Assembly (AIA) onboard NASA's Solar Dynamics Observatory. Designed
and built partially at the CfA and led by the Lockheed Martin Solar Astrophysics Laboratory, the AIA takes images of the Sun every twelve
seconds in seven different wavelengths of light to measure variations
in the Sun's atmosphere.



==========================================================================
They then made 3D simulations of solar flares and compared them to the observations.

The results show that most SADs are not generated by magnetic reconnection after all. Instead, they form on their own in the turbulent environment
and are the result of two fluids with different densities interacting.

Reeves says scientists are essentially seeing the same thing that happens
when water and oil are mixed together: the two different fluid densities
are unstable and ultimately separate.

"Those dark, finger-like voids are actually an absence of plasma. The
density is much lower there than the surrounding plasma," Reeves says.

The team plans to continue studying SADs and other solar phenomenon
using 3D simulations to better understand magnetic reconnection. By understanding the processes that drive solar flares and eruptions from
the Sun, they may ultimately help develop tools to forecast space weather
and mitigate its impacts.

Additional co-authors on the paper are Xiaoyan Xie of the CfA; Sijie
Yu of the New Jersey Institute of Technology; and Vanessa Polito of the
Bay Area Environmental Research Institute.

This research was supported by grants from the National Science
Foundation.

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


========================================================================== Related Multimedia:
* Video_of_supra-arcade_downflow_within_a_solar_flare ========================================================================== Journal Reference:
1. Chengcai Shen, Bin Chen, Katharine K. Reeves, Sijie Yu, Vanessa
Polito,
Xiaoyan Xie. The origin of underdense plasma downflows associated
with magnetic reconnection in solar flares. Nature Astronomy,
2022; DOI: 10.1038/s41550-021-01570-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220127114332.htm

--- up 7 weeks, 5 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)