On seeing the recent startling clear solar images from the Daniel K. Inouye Solar Telescope, many may wonder how the images can exceed those from the Solar Dynamics Observatory Telescope - actually orbiting 5, 610 miles above the Earth's surface - to be able to observe the Sun with no interfering atmosphere:
Recall I posted about the latter's achievements last year when Janice and I attended a scientific conference ('the Helio Hive') in Boulder, e.g.
Looking Back On Last Week's Solar Dynamics Workshop - One Of The Best Meetings I've Ever Attended
The purposes and methods distinguishing the two craft: are actually fairly straightforward to spell out:
- The DKIST (for short) features a 4-meter primary mirror, making it the world's largest solar telescope. This enables it to resolve solar features 18-39 km across.
- By contrast, the SDO instrument has only 0.2m diameter, with the resolution limit now in the 300-600 km range.
- The DKIST is particularly geared to identifying the fine scale (~ 20 km) plasma vortices on the solar surface (top image) driven by the Kelvin-Helmholtz instability.
- By contrast, the SDO's advantage is in capturing full disk images i.e. check out:
across multiple EUV and UV wavelengths without atmospheric interference.
E.g. note these images from SDO:
Continuing with the differences:
- The ground-based DKISTI (near the summit of Haleakalā, a volcano on the Hawaiian island of Maui,) relies heavily on advanced adaptive optics to correct for Earth's atmospheric blurring, but gains massive light-gathering power from its 4-meter mirror
-The SDO - in a Space-based (geosynchronous orbit) - avoids Earth’s atmosphere entirely, allowing unobstructed viewing of ultraviolet and extreme-ultraviolet wavelengths that ground-based telescopes cannot see.
Getting back to the National Science Foundation’s Daniel K. Inouye Solar Telescope, we now understand that within those high resolution plasma vortices we have uncovered a hidden process that drives solar activity. This is known as the Kelvin-Helmholtz instability, or KHI- underpinning the swirling patterns such as exposed in the top image. This 'KHI' could explain solar mysteries, such as why the sun’s corona, or outer atmosphere, is much hotter than its surface.
The vortical swirls could also fuel the buildup of the Sun’s magnetic energy, which drives solar flares and coronal mass ejections. When directed at Earth, the solar events known as CMEs (coronal mass ejections) are spawned - which activity blasts out particles that can disrupt satellites, power grids and other communications infrastructure.
The findings, published last Wednesday in the journal Nature, could help scientists understand the Sun’s behavior and activity, which is difficult to predict. The imagery and time-lapse vides from the DKIST reveal an unprecedented look at the Sun’s complex photosphere, the visible surface of which exists as a thin layer of atmosphere shaped by magnetic fields and currents of fluid plasma.
According to lead study author Dr. David Kuridze, assistant astronomer at the National Solar Observatory in Boulder, Colorado:
"Although theoretical models had suggested that the right
conditions for Kelvin-Helmholtz Instability could exist in the photosphere,
seeing these structures widespread across the surface was still a huge
surprise. The vortex
formation on the Sun has long been a central question in solar physics. For the
first time, we have identified both their origin and their driving mechanism.”
Kelvin-Helmholtz instability occurs when two fluids traveling at different velocities move past one another, creating tiny perturbations that result in spiraling vortices. Interested leaders can gain a deeper understanding with the following Youtube video:
Scientists have also observed this instability pattern in lake and ocean waves, cloud formation and the atmospheres of large gaseous planets such as Jupiter and Saturn. The images from the Inouye telescope mark the first time the phenomenon has been seen on the Sun.
According to UC Prof. Kuridze:
“KHI is a really efficient way for the Sun to break big plasma flows down into smaller motions,” Kuridze said. “When you have KHI in the system, it makes it much easier to trigger an energy cascade toward tiny, microscopic scales and once energy reaches those micro-scales, it can easily be released as heat. Therefore, finding KHI across the solar surface gives us a very important missing piece of the puzzle.”
The concept of storage of magnetic energy through “flux braiding,” has been known for some time in terms of magnetic field lines twisting together, e.g.
The braiding phenomenon can be seen clearly in this image of a solar prominence:
In all such cases the tension eventually becomes unstable, causing the tangle of magnetic fields to snap apart and then magnetically reconnect, releasing a burst of energy. If ample magnetic energy was stored a CME or major solar flare can result.
The problem was solar researchers never quite understood why these twisting patterns occurred in the first place. Fortunately, the new Inouye telescope observations offer a possible explanation. Swirls occurring along the edges of magnetic regions across the solar surface twist the fields together setting the stage for magnetic energy storage via braiding effect. The formations resulting also explain how heat makes its way to the Sun’s outer atmosphere.
Basically, the magnetic vortices generated by the Kelvin-Helmholtz instability effectively act like small-scale engines that can generate, transport and release energy throughout the solar surface. The constantly moving whirlpools can also act as energy stores for larger solar activity, such as flares and coronal mass ejections.
Then there are the 'nanoflares' the Sun is firing up every second. As the Nature study's lead author Kuridze noted:
“As it turns out, these micro-events are more influential for the Sun’s thermal and magnetic structure than rare, massive flares. There is a strong consensus within the solar physics community that unlocking global solar behavior begins with understanding these micro-scales. Solar magnetism is fundamentally shaped by these small-scale events, which ultimately drive the space weather that impacts Earth’s technological infrastructure.”
No comments:
Post a Comment