CMEs : A new method has been developed to determine the instantaneous expansion speed and radial size of Coronal Mass Ejections (CMEs) from the Sun when they pass over a spacecraft in the interplanetary medium.
The radial dimension of CMEs is crucial because it affects the duration of geomagnetic storms on Earth, which in turn impacts Earth’s communication systems. CMEs are magnetized plasma bubbles ejected from the Sun that evolve as they travel through space, driving geomagnetic storms that can severely disrupt both ground-based and space-based technologies, including communication systems, satellite orbits, and power grids.
The duration of magnetic disturbances on Earth caused by these storms is influenced by the radial size of a CME during its passage. However, understanding the changes in the radial size of CMEs has been difficult, as they expand due to pressure differences between the CME and the surrounding solar wind. Previous efforts to study the evolution of CMEs’ radial sizes have been limited.
Traditionally, the expansion speed of CMEs has been measured using single-point in situ data, but this approach is insufficient for estimating the instantaneous expansion speed. To address this challenge, astronomers from the Indian Institute of Astrophysics (IIA), a Department of Science and Technology (DST) autonomous institute, have developed a novel method that allows for estimating the instantaneous expansion speed of CMEs using data from a single-point spacecraft. This method is particularly useful for sub-L1 monitoring.
The researchers developed a technique to infer the accelerations of different CME substructures (such as the leading edge, center, and trailing edge) based on single-point in situ observations. These accelerations can then be used to estimate the CME’s instantaneous expansion speed.
“Our unconventional approach involves using the propagation speeds of two CME substructures at the same time to calculate the instantaneous expansion speed,” said Wageesh Mishra, a faculty member at IIA and co-author of the study.
This method also allows for the calculation of the radial size and the distance traveled by the CME substructures at various moments in time.
“This study has important implications for understanding the duration of disturbances in Earth’s magnetosphere caused by CMEs,” said Anjali Agarwal, a Ph.D. student at IIA and the lead author of the study published on this work.
The method was demonstrated through a case study of a CME that erupted from the Sun on April 3, 2010, using data from NASA and ESA’s SOHO, STEREO, and Wind spacecraft. The researchers emphasized the importance of accurately estimating the expansion speed of a CME, particularly its substructures like the center and trailing edge, to predict the CME’s arrival time on Earth and its impact on space weather.
“Our approach, using a single-point in situ spacecraft, provides valuable insights. It shows that CME substructures evolve differently in the ambient medium, likely due to different forces acting on them,” explained Mishra.
Unlike previous studies, the researchers found that a CME experiences a change in its aspect ratio—measuring the radial dimension of the CME relative to its distance from the Sun—during its journey. The aspect ratio initially increases, then stabilizes up to a certain height, before decreasing systematically in the interplanetary medium.
“We are eager to apply this non-conventional approach to single-point in situ observations from India’s Aditya-L1 spacecraft, which will provide more insights into CME expansion,” Mishra added.