2016 SPD: Day 2


Editor’s note: This week we’re in Boulder, Colorado at the 47th meeting of the AAS Solar Physics Division (SPD). Follow along to catch some of the latest news from the field of solar physics!

Yesterday’s press conference provided an excellent overview of some of the highlights of this week’s SPD meeting. Four speakers provided their views on some of the hottest topics in solar physics at the moment, including “stealth” coronal mass ejections (CMEs), sunspot formation, long-term solar-activity trends, and the largest solar telescope ever built.

Stealth CMEs


Solar and Heliospheric Observatory (SOHO) composite image of a coronal mass ejection. [ESA/NASA/SOHO]

First up, Nathalia Alzate (Aberystwyth University) talked about recent success in solving the mystery of so-called “stealth” CMEs, massive solar storms that don’t exhibit the usual clues to their origin. Most CMEs have low-coronal signatures like flares, filament eruptions, jets, etc. that reveal the origin of the CME at the Sun. But stealth CMEs appear without warning, and seem to have no evidence of low-coronal signatures.

But are these signatures not there? Or could we just be missing them? Alzate and her collaborator Huw Morgan used advanced image processing techniques to search for low-coronal signatures associated with 40 CMEs that have been classified as stealth CMEs. Their techniques enhance the observed structure down to fine spatial scales, and help reveal very faint dynamic events.

Sure enough, these processing techniques consistently revealed low-coronal signatures for every single supposed stealth CME they examined. This suggests that all CMEs exhibit some signatures in the low corona — it’s only a matter of being able to process the images well enough to detect them!

Spectacular Sunspot Simulations

Still image from a simulation studying sunspot formation. Compare to the cover image of sunspot observations! [Feng Chen, Matthias Rempel, & Yuhong Fan]

Still image from a simulation studying sunspot formation. Compare to the cover image of sunspot observations! [Feng Chen, Matthias Rempel, & Yuhong Fan]

Next up, Feng Chen (High Altitude Observatory) described recent computational advances in simulating sunspot formation. He and his collaborators have used high-performance computing to build a model that successfully reproduces many of the key properties of sunspots that are observed.

In particular, these simulations track the motions of the magnetic field starting within the interior of the Sun (8000 km below the surface!). The magnetic field is generated and intensified by convection deep within the solar interior. Bundles of magnetic field then rise through the convection zone, eventually breaking through the solar surface and giving rise to sunspots.

This process of tracking the flow as it travels from the convective layer all the way through the solar surface has resulted in what may be some of the highest fidelity simulations of sunspots thus far. The structures produced in these simulations compares very favorably with actual observations of sunspots — including the asymmetry seen in most sunspots.

Counting Spots on the Sun

Continuing the discussion of sunspots, Leif Svalgaard (Stanford University) next took us on a historical journey from the 1600s through the present. For the last 400 years — starting with Galileo — people have kept records of the number of sunspots visible on the Sun’s disk.

Galileo sunspots

One of Galileo’s drawings of his sunspot observations from 1612. [The Galileo Project]

This turns out to be a very useful practice! Total solar irradiance, a measure used as input into climate models, is reconstructed from sunspot numbers. Therefore, the historical record of sunspots over the last 400 years impacts our estimates of the long-term trends in solar activity.

Based on raw sunspot counts, studies have argued that solar activity has been steadily increasing over time. But could this be a misinterpretation resulting from the fact that our technology — and therefore our ability to detect sunspots — has improved over time? Svalgaard believes so.

By studying and reconstructing 18th century telescopes, he demonstrates that modern-day sunspot counts are able to detect three times as many sunspots as would have been possible with historical technology. When you normalize for this effect, the data shows that there has therefore not been a steady increase long-term in sunspot numbers.

World’s Largest Solar Telescope

The final speaker of the press conference was Joe McMullin (National Solar Observatory), who updated us on the status of the Daniel K. Inouye Solar Telescope (DKIST). This 4-meter telescope will be the world’s largest solar telescope, and the first new solar facility that the US has had in several decades.

The DKIST team and facilities, as of March 2016. [NSO]

The DKIST team and facilities, as of March 2016. [NSO]

The technology involved in this spectacular telescope is impressive. Its thin, enormous mirror is polished to within an error of nearly 1/10,000th of a human hair! Underlying the telescope is the most complex solar adaptive optics systems ever created, with 1600 different actuators controlling the system real-time to within an error of 4 nanometers. In addition, the entire facility is designed to deal with a tremendous heat load (which can severely limit the quality of observations).

DKIST’s construction on Haleakala in Hawaii has been underway since 2012, and is making solid progress. The majority of the structures have now been completed, as have most of the major telescope subsystems. The primary hurdle that remains is to integrate all the of components and make sure that they can perform together — no small feat!

DKIST is expected to begin science operations in 2020, with ~10-20 TB of data being produced each day. This data will be freely and immediately accessible to both researchers and the public.