ARIES Solar Physicists Develop a Novel Technique for Tracking the Solar Eruptions

The solar eruptions from the Sun’s atmosphere (corona) known as coronal mass ejections (CMEs) comprise large amount of plasma and magnetic field which are responsible for the space-weather. It has been known  that CMEs accelerate in the lower corona. Just like any other accelerating object, the distance (height)-time plot of accelerating CMEs shows a parabolic profile. With the advancement in space technology, there has been tremendous increase in the amount of data obtained from spacecrafts. To identify and track the solar eruptions in huge number of images can become tedious, if done manually.

In the past, scientists had developed a software named Computer Aided CME Tracking Software (CACTus) based on a computer vision algorithm, linear Hough transform, that could detect and characterise such eruptions automatically in the outer corona (>3 Rsun) where these eruptions cease to show accelerations and propagate with a nearly constant speed. However, this algorithm can not be applied to the inner corona observations due to the vast acceleration experienced by these eruptions thus displaying parabolic ridges in the height-time diagram. Even though Hough transform had been used to automatically detect lines and circles etc. in the images, it has not been used to detect parabola in the images, probably because the parameters to describe a unique parabola are more than those required to describe a straight line.

The research led by Mr. Ritesh Patel, Dr. Vaibhav Pant and Prof. Dipankar Banerjee from ARIES, Nainital, an autonomous institute under DST, Government of India, along with their collaborators from Royal Observatory of Belgium have led to the development of an algorithm, CMEs Identification in Inner Solar Corona (CIISCO) to detect and track the accelerating solar eruption in the lower corona. This algorithm is based on the use of parabolic Hough transform to automatically detect the presence of parabolic profiles in the height-time plots of the solar eruption. An example of such implementation of the CIISCO on extreme ultraviolet (EUV) wavelength image of SWAP instrument is shown in Figure 1 where an eruption is tracked using the parabolic Hough transform. CIISCO also provides the characteristics of these eruptions including the width, speed and acceleration. CIISCO has been successfully tested on several eruptions observed by space observatories including Solar Dynamics Observatory and Solar Terrestrial Relations Observatory, PROBA2/SWAP launched by NASA and ESA respectively.

                             (a)                                                                (b)                                             (c)

Figure 1:(a) Solar corona observed in EUV image of SWAP instrument. An erupting structure at the west limb is pointed at by the red arrow, (b) height-time plot corresponding to the eruption. A parabolic profile could be observed, (c) Identified parabolic profile by CIISCO overplotted on (b) by dashed line.

The parameters determined by CIISCO are useful to characterise these eruption in the inner corona, a region where the properties of such eruptions are less known. An implementation of CIISCO on the large volume of data available from the instruments mentioned above will be helpful to improve our understanding of the kinematics and expansion of the eruptions in the inner corona. It is worth noting that India’s first solar mission, Aditya-L1, will be observing this region of the solar corona. After the launch of Aditya-L1, implementation of CIISCO on the Aditya-L1 data will provide new insight in to the CME properties in this less explored region.

This research has been published in the Solar Physics journal and the details could be found in the following links:

https://link.springer.com/article/10.1007/s11207-021-01770-z

https://arxiv.org/abs/2010.14786

This story is also available on DST website.