The research: Understanding the processes that trigger a solar flare through a computer simulation model, so that these can be predicted
On November 4 last year, the Swedish airspace was closed for more than an hour following radar malfunctions at some of its airports. Flights disappeared from radar screens, causing a blackout. The problem was traced to disturbances in the Earth’s magnetic field near the area.
These disturbances in the magnetic field were caused by what are known as solar flares, a sudden burst of highly energetic electromagnetic radiation from the surface of the Sun. The energy accompanying the most energetic of these solar flares is equivalent to that contained in billions of hydrogen bombs.
These electromagnetic bursts often interfere with the Earth’s magnetic field and can result in different kinds of impacts. On March 13, 1989, for example, the hydroelectric transmission system in Quebec, Canada, suffered an outage for eight-nine hours, and it was once again found to be triggered by solar flares.
Because of the kind of havoc it can cause on Earth, it is important for us to guard ourselves and our vital installations from solar flares in future. Efforts are being made to understand the processes that trigger a solar flare, so that these can be predicted and a warning can be issued.
But right now, we are several steps away from that objective. What we do know is that most of the solar flares originate from ‘sunspot’ regions on the surface of the Sun. Some of these sunspots are bigger in area than the Earth, a few even equal to Jupiter in area, but show up as tiny regions on the Sun’s surface. These sunspots are highly magnetised regions and are cooler than surrounding areas of the Sun. The solar flares are observed to originate right above these regions. The magnetic forces over sunspots are so stressed that beyond a threshold they get released in a blast of energy.
The phenomenon is similar, in a way, to earthquakes which also happen when mechanical stress, as a result of movement of landmass below the surface, becomes unbearable to store.
There is a certain kind of sunspot, called ‘delta’ sunspot, that accounts for almost 95 per cent of all X-ray radiation reaching the Earth’s surface. In the delta sunspots, the magnetic poles, north and south, lie very close to each other, because of which the magnetic forces are exceedingly stressed. These sunspots continue to release energy through multiple solar flares.
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For a few years now, we have been trying to recreate the solar flare conditions through our computer simulation models. None of the existing computer simulations has come close to reproducing the amount of energy released during a typical solar flare. Our new simulation is a significant improvement over the existing ones and generates a very promising picture of a solar flare.
Our physical equations take into account the effect caused by the rotation of the Sun, something that the existing simulations never did. Like the Earth, and many other heavenly bodies, the Sun also rotates around its axis, and it goes around once in 27 days. This rotation twists the magnetic fields inside the Sun’s surface, leading to further magnetic stress.
We believe our computer simulation model is a big step forward in understanding solar flares, but a lot of work still needs to be done. The next step is to test the model with actual solar observations from the past, to test whether it can recreate solar flares that have already occurred. If we are able to manage that successfully, we can start working on a prediction model for solar flares.
These results of our simulation model were published in the Physical Review Letters journal under the title, ‘Modeling Repeatedly Flaring Delta Sunspots’.
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By: Piyali Chatterjee, IIAP, Bangalore; Viggo Hansteen & Mats Carlsson, Institute of Theoretical Astrophysics, University of Oslo, Norway