Earlier this month, earth experienced a significant solar storm due to activity in the solar region known as AR13664. This region unleashed several X-class flares and coronal mass ejections (CMEs) directed towards Earth, which led to a geomagnetic storm—the most severe since 2003—with an equatorial Disturbance Storm-Time (Dst) index of -412 nanoteslas (nT), causing disruptions in our GPS systems and communication.

This event was the strongest geomagnetic storm since 2003, with the area of solar activity as large as the one from the Carrington Event in 1859. The Carrington Event was a massive solar storm that hit Earth, causing widespread telegraph disruptions and producing brilliant auroras visible even near the equator. “Geomagnetic storms are disturbances in Earth’s magnetic field triggered by solar winds and flares, and can disrupt communication systems, power grids and navigation technologies,” explains Girish Linganna, defence and aerospace analyst.

According to him, the Dst index, which measures the intensity of geomagnetic storms, reflects significant disruptions to Earth’s magnetic field caused by these solar activities. A lower Dst index, particularly more negative values, indicates a stronger geomagnetic storm, highlighting the profound impact that such solar phenomena can have on modern technology. 

The geomagnetic storm index, also referred to as the Kp index, measures the strength of Earth’s geomagnetic disturbances on a scale of 0 to 9. It recently reached the maximum level of 9, signifying an extremely intense geomagnetic storm.

 What Is the Solar Region AR13664?

It refers to a specific area on the Sun, cataloged as Active Region 13664, where magnetic activity is heightened. Active regions are parts of the Sun’s photosphere—the visible surface—characterized by strong magnetic fields. This increased magnetic activity can lead to such phenomena as solar flares and CMEs.

“The placement of active regions, such as AR13664, can vary widely across the Sun’s surface and changes as the sun rotates. These regions can be located in either the northern or southern hemisphere and their position can shift over time.

These regions are also associated with sunspots, which are cooler, darker areas on the Sun’s surface. Sunspots appear darker because the concentrated magnetic field flux in these areas blocks the flow of heat. Each active region is given a unique number, allowing scientists to monitor and study their development and their potential impact on space weather,” says Linganna. 

Halo CMEs Directed at Earth

According to reports in the public domain, numerous M-class and C-classsolar flares have occurred recently, many accompanied by halo CMEs aimed directly at Earth. Halo CMEs involve clouds of plasma and magnetic fields which, when observed from Earth, seem to form a halo around the Sun. This halo appearance indicates that the CME is directed towards us, increasing the likelihood of impacts on Earth, such as geomagnetic storms.

High-energy particles from these halo CMEs were responsible for the intense geomagnetic storms observed early on May 11, 2024. “But the impact of the storm on India was minimal since it struck in the early hours of May 11, when the ionosphere—a layer of Earth’s atmosphere containing charged particles created by solar radiation, which helps transmit radio waves around the planet—had not formed fully. Additionally, India’s lower latitude helped avoid major outages,” explains Linganna.

In contrast, the ionosphere experienced significant turbulence over the Pacific and American regions. 

Potent X-Class Flare Detected

At the same time as the Solar storm hit, a potent X-class flare, classified as X 5.8, was detected. X-class flares are the most intense type of solar flares, with a peak energy output exceeding 0.0001 watts per square metre (>10^-4 W/m^2). These flares are powerful enough to cause significant disruptions on Earth.

Solar flares are powerful bursts of energy resulting from the reconnection of magnetic fields, and are classified on a scale of B to X, with each category indicating a 10-fold increase in intensity. Such pronounced geomagnetic activity, as indicated by the peak Kp index, can greatly disrupt operations of satellites, power networks and GPS systems.

In recent days, several X-class flares and CMEs have impacted Earth, severely affecting high-latitude regions, or areas close to the Earth’s poles. According to reports, this has led to diversion of transpolar flights—airplane routes that fly directly over the Earth’s poles, for instance, the Delhi-San Francisco Passover, or close to the North Pole, optimizing travel distance between India and the US West Coast. This is one of the more common examples of a long-haul flight from India that takes advantage of the polar route for efficiency.

Additional solar events are anticipated in the coming days.

 Next Intense Flares Are M-Class

Following X-Class in intensity are M-class flares, which have an energy range of 0.00001 to 0.0001 watts per square metre (10^-5 – 10^-4 W/m^2). Although less powerful than X-class flares, M-class flares can still disrupt satellite and radio communication. Understanding these measurements helps scientists assess how solar flares might impact our planet. 

Perspectives from the Ground Level

Data from the Global Navigation Satellite System (GNSS) network at the National Atmospheric Research Laboratory (NARL), in Gadanki, Andhra Pradesh (located at 13.4593° N, 79.1684° E), indicated a significant reduction in the Total Electron Content (TEC). There was a decrease of over 50% from the night of May 10 till the morning of May 11. During the day on May 11, the TEC was approximately 10% higher than usual, with significant fluctuations, suggesting a disturbed ionosphere. By evening, the TEC had increased by nearly 30%. No L-band scintillation was detected.

“Following the geomagnetic storm on the day, there was a notable increase in TEC values in Trivandrum after 8 UT (Universal Time). By 10 UT, the increase exceeded 100% compared to the baseline observed on May 9 and May 10. At 9 am IST in Trivandrum, the plasma measured about 80 TECu—note that one TECu represents 10^16 electrons per square meter in a column-integrated view. This is significantly higher than the usual TEC values for the same local time, which typically range from 10 to 20 TECu,” says Linganna.

Additionally, radar data did not show any bubbles, which aligns with the TEC and scintillation measurements taken by GNSS receivers. L-band scintillation refers to rapid fluctuations in radio wave signals caused by irregularities in the ionosphere, affecting communication and navigation systems that operate on L-band frequencies.

While these were the findings from Gadanki, data reported by the Thumba node of the Indian Network for Space Weather Impact Monitoring (INSWIM), located at coordinates 8.5310° N, 76.8750° E, showed even more dramatic changes. This is anticipated since the ionospheric ring current, which intensifies during geomagnetic storms, moves across the sky above Thumba. 

Perspectives Gathered from the Space

ISRO has activated all its observational tools and systems to capture the details of this event. The Aditya-L1 and Chandrayaan-2 missions have collected data and analysed the findings. 

Observations by Aditya-L1

Currently, the Aditya Solar Wind Particle Experiment (ASPEX) instrument on Aditya-L1 is detecting fast solar winds, hot solar wind plasma, and strong flows of energetic ions. ASPEX comprises two cutting-edge instruments—the Solar Wind Ion Spectrometer (SWIS) and STEPS (Supra-Thermal and Energetic Particle Spectrometer).

“The SWIS instrument has two main parts, each called a Top Hat Analyzer, that help study space particles. The first part, THA-1, can identify and measure two specific types of particles, alpha particles and protons, separately. It looks at these particles in a wide circle that matches the path that Earth takes around the Sun. The second part, THA-2, measures all types of particles together, also in a wide circle along Earth’s orbit. This helps scientists learn more about the particles that come from the Sun and other sources in space,” Linganna explains.