Upgraded solar telescope brings scientists closer to predicting solar flares

A major upgrade to the Swedish 1-m Solar Telescope (SST) on the Spanish island of La Palma is opening new frontiers in solar research. With a wider field of view that does not compromise image quality, the Stockholm University operated telescope has now enhanced capabilities to measure light polarisation across new wavelengths, providing scientists with unprecedented tools to map the Sun’s magnetic field. This marks a crucial step towards forecasting solar flares (phenomena that can disrupt communications and power systems on Earth) bringing space weather prediction closer to reality.

The telescope works by directing sunlight through a lens at the top of a tall tower down into a basement, where the light is divided between various scientific instruments. The updated system features the replacement of the CRISP instrument which operated in red light, with the new CRISP2 instrument, revealing a substantial increase in the field of view: 120 arc seconds, corresponding to 86,000 km on the Sun's surface.

CHROMIS, which observes blue light, has new detectors providing a larger field of view and it has also been supplemented with a polarimeter to measure the polarisation of light, i.e. its plane of oscillation.

This will enable us to measure magnetic fields by observing the H and K spectral lines, hopefully at higher altitudes in the solar atmosphere than has previously been possible,” says Dan Kiselman, assistant director of the Institute for Solar Physics at Stockholm University’s Department of Astronomy.

Maps of the solar atmosphere

Spectral lines are formed in the solar atmosphere when atoms absorb or emit light at specific wavelengths, or colours. By observing certain spectral lines, information can be obtained about different layers of the Sun’s atmosphere, and phenomena that propagate vertically can be tracked.

“One of our goals is to create reliable maps of the solar atmosphere’s structure and magnetic field, so that we can follow what is going on and in the future even learn to predict what will happen based on the data we collect,” says Kiselman.

^{Sunspot observed with CHROMIS. (A) Image in normal light. B) The same area imaged in the H spectral line. The upper layers of the sun's atmosphere, known as the chromosphere, are visible. (C) A preliminary estimate of the magnetic field in the chromosphere, based on polarisation data. The two parts of the sunspot have opposite magnetic polarity (red and black), and the boundary between them is remarkably sharp. Image: Jorrit Leenaarts/Institute for Solar Physics. ©SU}

Northern Lights and magnetic storms

The Sun experiences bursts of energy so powerful that they can affect Earth. One such example is solar flares, which can be likened to magnetic short circuits initiated at high altitudes above the sun’s surface, where unfortunately, it is difficult to take measurements.

Another example is ‘coronal mass ejections’, which are clouds of plasma thrown off by the sun. These take a couple of days to reach Earth, where they collide with the magnetosphere: “This creates auroras and magnetic storms, which can cause problems for our technological systems,” explains Dan Kiselman.

"We need to stay one step ahead"

Most of the time, ordinary people on Earth do not notice solar eruptions, but there are risks when they become particularly strong. For example, there is a risk of high levels of X-ray radiation in the upper atmosphere, which can affect radio communication.

An additional risk is that a large solar flare could disrupt or even pose damage to electrical installations on Earth, and in the worst case, entire power grids.

To prevent these risks, further knowledge about solar flares is required, such as how they are triggered. In the future this will enable us to predict them based on observations. But "to achieve that goal, we need to be able to map the physical conditions higher up in the solar atmosphere. We also need a wide field of view to increase our chances of covering an eruption in real time when it occurs,” says Dan Kiselman.

Once the technical conditions are in place, constant readiness is required. Even though the conditions at La Palma are perhaps the best on Earth, it is usually the atmosphere that sets limits on how good the data will be.

It's like when you see air above hot asphalt on a very hot day. The air shimmers and the images through the telescope become blurred and distorted. We can correct for some of these effects, but ultimately it is when conditions are almost perfect that you get really useful data. A lot of time is therefore spent waiting for the right conditions and stable air and we can't let a single day go to waste because you never know when that moment will come. Then everything has to work”, stresses Kiselman.

When the Earth’s atmosphere is stable and an important event occurs on the Sun, such as a large solar flare, unique data is collected.

The control room at the Swedish Solar Telescope (SST). Photo: Dan Kiselman ©SU

About the SST

The Swedish 1-m Solar Telescope (SST) is one of the world’s highest-resolution solar telescopes and still one of the world’s most advanced solar telescopes despite its twenty-three years of service.

The new technical upgrade consolidates the SST’s position as a world leader in the field. Its combination of image quality, field of view size, and advanced instruments that can all work in parallel, is unique.

Find out more from the original story, in Swedish.

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