Observations by Aditya-L1 help decode unusual dawn-time geomagnetic disturbances during strong solar storms

Observations and measurements made by India’s maiden solar mission, Aditya-L1, have helped to decode the unusual dawn-time geomagnetic disturbances during strong solar storms.

Geomagnetic storms are large disturbances in Earth’s magnetic field caused by changes in the solar wind- a continuous flow of charged particles released from the Sun.

“When sudden increases or decreases in solar wind pressure strike Earth’s magnetic shield (the magnetosphere), those can trigger sharp changes in the magnetic field,” the Indian Space Research Organisation (ISRO) said.

During the peak phase of Solar Cycle 25, two very intense geomagnetic storms occurred on 10 May and 10 October 2024.

These storms produced widespread magnetic disturbances and spectacular auroras that were visible even at unusually low latitudes.

Scientists noted a particularly striking feature during both storms in the form of an unusual pattern in the response of the Earth’s magnetic field. Under normal circumstances, when solar wind dynamic pressure suddenly increases, most low-latitude regions of the Earth experience a positive (enhanced) magnetic perturbation.

When pressure suddenly decreases, a negative (decreased) magnetic perturbation is seen.

“However, during these two strong storms, scientists observed magnetic field perturbations of opposite polarities in the dawn sector. Remarkably, these anomalous behaviors were not seen over other stations which were at different local times,” the ISRO said.

It further said that during the 10 May event (during sudden increase in solar wind dynamic pressure), most low-latitude regions showed positive (enhanced) magnetic perturbations, but dawn-side stations recorded a negative (decreased) perturbation.

“During the 10 October event (during sudden decrease in pressure), most low-latitude regions showed a decrease, but dawn-side stations recorded an increase,” it said.

Using the observations of particles and field measurements from Aditya-L1 and combining those with measurements from an extensive global network of ground-based magnetic field measurements, scientists from various academia (led by the Indian Institute of Geomagnetism, Mumbai), in collaboration with the ISRO scientists identified these unusual signatures.

“The study reveals that these unusual dawn-side magnetic disturbances are most likely caused by a special type of space current normally confined to auroral (high-latitude) regions. During very strong storms, when the Earth’s magnetosphere becomes highly compressed, such auroral current systems ingress into lower latitudes, extending much farther towards the equator than usual- but primarily in the dawn sector,” the ISRO said.

It further added that this explains why low-latitude stations near dawn recorded magnetic disturbances opposite to those seen at similar latitudes elsewhere around the globe.

“Understanding how Earth’s magnetic field responds due to sudden changes in solar wind dynamic pressure is important because such rapid magnetic variations can influence technological systems such as satellites, navigation systems, power transmission networks etc,” the space agency said.

The combined observations from the Aditya-L1 spacecraft and global ground magnetometer networks have provided new insights about how extreme solar wind conditions can alter the normal pattern of geomagnetic disturbances particularly near dawn local times during intense geomagnetic storms.