Many Eyes on the Solar Storm

A conversation with solar astronomer Piyali Chatterjee reveals that there’s a lot more to the ongoing geomagnetic storm than the mesmerising aurorae in the sky.
By | Published on May 13, 2024

Over the past 72 hours, photographs of mesmerising green, blue, pink and purple skies have been cropping up in our social media feeds and Whatsapp inboxes. It seems aurorae, typically associated with the Scandinavian region, have been sighted in North America, in Europe and, on Saturday, in Ladakh! As the dust settles, we are hearing talk of solar flares and geomagnetic storms. In fact, astronomers are warning that there may be reason for concern. What exactly is happening? I had a brief conversation with solar astronomer Piyali Chatterjee at Indian Institute of Astrophysics (IIA), Bengaluru, to break it all down.

The first thing to know is that we are currently in the middle of a solar maxima. This refers to the point in the 11-year solar cycle when the rate of activity on the sun is the maximum, usually synonymous with the number of ‘sunspots’ observable on its surface. Sunspots are temporary dark patches on the sun where the magnetic field is especially strong and the temperature is relatively low. 

After a weak previous cycle, this particular one is looking very strong. “Suddenly, in the last few months, the sun has been looking very active, with big sun spots. These are the areas where solar flares originate,” pointed out Piyali. 

Solar flares are violent explosions that occur in the sun’s atmosphere when hot plasma comes into contact with magnetic fields. “When oppositely directed magnetic fields come close to each other, it’s like a singularity,” described Piyali. Here, a singularity indicates a region where electric current goes to infinity. “Nature tries to smooth out the singularity through a release of electromagnetic radiation.”

As fantastical as all this sounds, this is just business as usual for the sun. What is special is the rate at which this is currently happening. And the fact that some of these solar flares are resulting in a related phenomenon called coronal mass ejections (CME). Astronomers classify flares according to their strength; it is the most energetic of them, the X flares, that have the most chance of having a corresponding CME. Between 10 and 11 May, there were at least four such CMEs that were detected by a NASA spacecraft, all emerging from one particular active region of the sun called AR13664.

Piyali Chatterjee

“If there is a super active region continuously flaring, some of these flares will be earth-directed, and when they hit our magnetic field, they cause geomagnetic storms,” said Piyali. Can we perceive these storms in our everyday life? Unlikely, according to Piyali. “As the solar cycle oscillates, there may be changes in the luminosity of the sun, but very very small ones,” she said.

What we can perceive, however, is a potential spurt of aurorae, colourful displays caused by the interaction of charged particles from the sun colliding with oxygen and nitrogen atoms in the earth’s atmosphere. While aurorae are usually visible near the poles, where the Earth’s magnetic field is strongest, in times of intense solar activity, they can be seen in lower latitudes as well, explaining the sightings in North America and in Europe.

Notably, the red, blue and violet bands seen at Hanle and Merak in India’s Ladakh are not exactly the regular aurorae, but Stable Auroral Red arcs. According to Dorje Angchuk, who works as an engineer at IIA’s observatory at Hanle, these are more stable than the aurorae, remaining in the sky for several hours.

While solar flares can travel at the speed of light (taking about 8 minutes to reach Earth), CMEs are slowed down by atmospheric drag, taking hours, or sometimes days to reach Earth. This gives astronomers time to predict the arrival of a CME in advance. While there exist models that can do this to different degrees, Piyali said that astronomers still have some way to go.

Suddenly, in the last few months, the sun has been looking very active, with big sun spots. These are the areas where solar flares originate — Piyali Chatterjee

As it turns out, a head start could be really helpful to us. “While a strong geomagnetic storm is not an apocalypse, it could affect the economy, in a world where we are investing so much into technology,” Piyali said. She took the example of air traffic control, which relies on radio waves. “During a solar storm, the height and properties of Earth’s ionosphere changes, thereby affecting radio waves which propagate in the ionosphere. Planes that fly polar routes, especially, could be affected by this,” she points out. Similarly, extreme solar storms could cause errors in GPS navigation, disrupt communication, power grids and corrode oil pipelines.

An image of the sunspot group AR13664 taken at 9 AM on 8 May 2024, from Kodaikanal Solar Observatory. Credit: IIA

These aren’t mere speculations. The last solar storms of similar intensity to the ongoing one happened in 2003, two solar cycles ago. Dubbed the ‘Halloween solar storms’, they caused aircraft to be rerouted, a power outage in Sweden, and the destruction of an experiment aboard NASA’s Mars Odyssey orbiter. It also resulted in aurorae as far south as Texas, USA, and some of the Mediterranean countries.

Being near the tropics, India has less to worry about, reassured Piyali, but solar storms are certainly something to be concerned by as India expands its space assets. “We have to protect our satellites, and before our human spaceflight programme takes off, we need to do a proper study on this.”

The risks notwithstanding, such extreme geomagnetic storms present rare opportunities for solar astronomers to learn more about the sun. Aboard ISRO’s Aditya L1, Piyali reminded, is an instrument called the Solar Low Energy X-ray Spectrometer (Solex), which is designed to study the X-ray flares from the Sun. “However, Aditya L1 is still at a performance verification stage, so it is still too early to use it to observe flares,” she said. Piyali expects a slew of publications to come out of the solar community in the near future.

As Annapurni Subramaniam, Director of IIA, mentions in the official press release, “It is not very often that we see aurorae at Hanle latitudes –  we look forward to observing many more such aurorae from Ladakh during this solar cycle.”

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