Coronal Mass Ejections (CMEs): A novel method has been found to determine the instantaneous expansion speed and radial size of Coronal Mass Ejections (CMEs) from the Sun when it passes over a spacecraft at a single-point in the interplanetary medium.

• It governs CME longevity and geomagnetic storm duration, impacting Earth’s communication systems.
• About CMEs: Magnetized plasma bubbles from the Sun that cause geomagnetic storms, disrupting communications, satellites, and power grids.

o CME Expansion in Space: Expansion due to pressure differences with the solar wind affects their radial dimension, which has been inadequately studied.

o Existing Measurement Limitations: Previous single-point in situ methods are insufficient to estimate instantaneous expansion speed.

• New Non-Conventional Approach: Developed by Indian Institute of Astrophysics (IIA) under the Department of Science and Technology (DST).
• Infers accelerations of CME substructures (leading edge, center, and trailing edge) from single-point observations.

o Uses propagation speed of any two substructures to determine instantaneous expansion speed.

o Computes radial size and distance traveled by CME substructures at various points.

• Case Study: Demonstrated on a CME from April 3, 2010, using data from NASA & ESA SOHO, STEREO, and Wind spacecraft.
• Key Findings: CME substructures evolve differently due to varying forces.

o CME’s aspect ratio first increases, remains constant, then decreases in interplanetary space.

• Future Applications: Method to be tested using Aditya Solar Wind Particle Experiment (ASPEX) on Aditya-L1, India’s first space-based solar observatory.

o Helps in accurate prediction of CME arrival time and its effects on space weather.