Non-conventional approach to measure the radial dimension of CMEs can help predict adverse effects on Earth

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.

The radial dimension of CMEs governs the longevity of the CMEs and their associated geomagnetic storms on the Earth and hence it is important to determine it, to predict the influence of the CMEs on the Earth’s communication system.

CMEs are magnetized plasma bubbles ejected from the Sun and evolve in the interplanetary medium. They are the major drivers of perturbations in the Earth’s magnetic field, known as geomagnetic storms. Such storms can cause severe impacts on ground and space-based technological systems, such as communication disruptions, deorbiting satellites, and power grid failures.

The duration over which the Earth experiences such a magnetic perturbation is influenced by the radial dimension of a CME, along with other parameters, during its passage over the Earth. The changes in the radial dimension of CME depend on its expansion in the interplanetary medium, which has yet to be adequately understood. CMEs expand during their journey due to the pressure difference between CME and ambient solar wind. Limited efforts have been made to investigate the evolution of radial sizes of CMEs so far.  

The measurements of expansion speeds of CMEs have been done mostly utilizing single-point in situ measurements, which are known to be insufficient to estimate the instantaneous expansion speed of CMEs. 

In order to overcome this challenge, Astronomers at the Indian Institute of Astrophysics, an autonomous institute of the Department of Science and Technology (DST), devised a novel method to estimate a CME’s instantaneous expansion speed even using a single-point in situ spacecraft and will be helpful for sub-L1 monitors.

They found a method to first infer the accelerations of CME substructures (leading edge, center, and trailing edge) even from single-point in situ observations that are used to estimate their propagation speeds at an instant. This can be used for estimating the instantaneous expansion speed. 

“Our non-conventional approach utilizes the propagation speed of any two CME substructures at the same instance to determine the instantaneous expansion speed,” said Wageesh Mishra, a faculty at IIA and a co-author of the study.

This approach also computes the radial size and the distance traveled by the CME substructures at various instances as well.

“This study has implications for understanding the longevity of perturbations on the Earth’s magnetosphere caused by CMEs,” said Anjali Agarwal, a Ph.D. student at IIA and the first author of the paper published on this work.