A solar flare that occurred on the Sun triggered a magnetic storm which scientists from Center of Excellence in Space Sciences India (CESSI), in Indian Institutes for Science Education and Research, Kolkata, had predicted will arrive at the Earth in the early hours of November 4, and they said that the magnitude of this storm would be such as to trigger spectacular displays of aurora (the coloured bands of light seen in the North and South poles) in the high-latitude and polar regions, just in time for the Deepavali celebrations in India. This prediction, which was based on models built by them and data from NASA’s observatories, seems to have come true, as people from several countries were tweeting pictures of aurorae.
Effect on atmosphere
Judging by data from the NASA DSCOVR satellite, the scientists observed a steep jump in transverse magnetic fields, density and speeds of the plasma wind that are tell-tale signatures of the arrival of a coronal mass ejection shock front, according to Dibyendu Nandi of CESSI Kolkata whose team predicted the event.
“This happened at 1.00 AM IST. We will know whether this is the CME flux based on its evolution as it passes through. These observations are taken at Lagrange Point L1,” he said on November 4, in a message to The Hindu.
Dipankar Banerjee, a solar physicist and Director of Aryabhata Research Institute of Observational Sciences (ARIES) based in Nainital said about the prediction, “This is quite promising. It appears their predictions are matching the observations.” He was not involved in this work.
From sunspots to solar storms
The solar magnetic cycle that works in the deep interior of the Sun creates regions that rise to the surface and appear like dark spots. These are the sunspots. Solar flares are highly energetic phenomena that happen inside the sunspots. In a solar flare, the energy stored in the sun’s magnetic structures is converted into light and heat energy. This causes the emission of high energy x-ray radiation and highly accelerated charged particles to leave the sun’s surface. Sometimes solar flares also cause hot plasma to be ejected from the Sun, causing a solar storm, and this is called Coronal Mass Ejection (CME). Coronal Mass Ejections can harbour energies exceeding that of a billion atomic bombs.
The energy and radiation and high energy particles emitted by flares can affect Earth bound objects and life on Earth – it can affect the electronics within satellites and affect astronauts. Very powerful Earth-directed coronal mass ejections can cause failure of power grids and affect oil pipelines and deep-sea cables. They can also cause spectacular aurorae in the high-latitude and polar countries. The last time a major blackout due to a coronal mass ejection was recorded was in 1989 – a powerful geomagnetic storm that took down the North American power grid, plunging large parts of Canada into darkness and triggering spectacular aurorae beyond the polar regions.
Predicting solar storms
The process of prediction takes place in two steps: First the researchers analyse the possibility of a strong solar flare from an active region – that is, clusters of sunspots – using
a machine learning algorithm which has been developed in CESSI, IISER Kolkata. “This algorithm needs observations of the sunspot magnetic fields, from which we extract various parameters to train the algorithm. We use data from NASA’s Solar Dynamics Observatory, specifically, the Helioseismic and Magnetic Imager instrument, for this purpose,” says Dibyendu Nandi, who, along with his PhD student Suvadip Sinha, developed the algorithm at CESSI.
The second step is estimating the time of arrival on Earth of coronal mass ejections and forecasting the geomagnetic storm. The group uses the near-Sun evolution of the coronal mass ejections through European Space Agency’s SOHO satellite and NASA's STEREO satellite to extract their speed. There is an associated flare, and its position on the Sun is used to extract the location of origin of the CME. The location of the source of the CME and the velocity are used as inputs by the group in a publicly available model widely called the Drag Based Ensemble Model to calculate the CME arrival times and speed. “This latter step has uncertainties as the physics of CME propagation is quite complex, but this is treated in a simplified manner in this model,” explains prof. Nandi. “When ISRO’s Aditya-L1 satellite is launched, we would be receiving similar data on solar storms from this observatory,” he adds.
Skies light up
Commenting on the work done by Prof Nandi and group, Dr Banerjee said, “This is their first comprehensive work on this… the basic physics input and the model seems to be robust.”
Some have been tweeting pictures of the aurorae seen in places such as Alberta in Canada, and Alaska, to name just a few. Prof Nandi further said, “Reports are already coming in which indicate we hit bull's eye with the prediction. Storm arrived within one hour of our forecast time with similar speeds to what we had estimated. Aurorae are being reported from unexpected countries such as Scotland, Ireland and states in the U.S. apart from the high latitude regions. Now NOAA Space Weather Prediction Center had upgraded the information on the geomagnetic storm resulting from the CME impact to be hazardous.”