Characterizing Solar Eruptions in Inner Corona using Ground and Space-based Data

Abstract

The solar corona is known to be associated with eruptions of large amount of magnetized plasma into the interplanetary space. In-spite of several years of ground- and space-based observations of the solar atmosphere, the inner corona (<4 Rsun) has not been explored in detail. As a result the initial dynamics of various eruptive features such as coronal mass ejections (CMEs), and associated plasmoids, extreme ultraviolet (EUV) eruptions, etc. have not been understood completely. Aditya- L1 is India’s first space-based mission to study the Sun from the Lagrange 1 (L1) position scheduled to be launched in 2022-23. Visible Emission Line Coronagraph (VELC) is one of the seven payloads on-board Aditya-L1 and will probe the inner corona from 1.05 – 3 R with 10 ˚A pass-band centred at 5000 ˚A with high spatial (2.51 arcsec pixel−1 ) and temporal (10 s cadence) resolution. The main aim of VELC is to probe the inner corona with high resolution imaging and spectroscopy while capturing the initial dynamics of solar eruptions. This thesis is dedicated to the development of automated algorithms, enhancement of the coronal images to identify and characterize the solar eruptions in the inner corona at different spatial and temporal scales. The VELC instrument is capable of taking high resolution images of the corona with high cadence. This could generate over 1 TB data by the continuum channel of this instrument alone. One of the major goals of the VELC is to understand the initial evolution of the CMEs. Due to the limited telemetry from the L1 point, we developed a simple algorithm to be implemented in on-board electronics based on intensity and area threshold to identify the images containing CMEs. The CME images will be sent back to Earth discarding the rest. This algorithm has been successfully tested on existing space-based and ground-based images of STEREO/COR-1A and K-Cor respectively and simulated CME images for VELC field of view (FOV). This will be one of the first on-board automated CME detection algorithm after the launch of Aditya-L1. It has been reported in previous studies that CMEs in the inner corona show acceleration profiles. As VELC will be observing this region, the study of initial kinematics of CMEs will be a primary objective. The existing ground-based algorithms for automated CME detection e.g. CACTus, SEEDS, ARTEMIS, etc, have not been successfully implemented to derive CME accelerations in the limited inner corona observations. So we developed an algorithm, CMEs Identification in Inner iii Solar Corona (CIISCO), based on Parabolic Hough Transform to automatically identify and track the CMEs/eruptions in this region and determine their kinematic properties. This algorithm has been tested in EUV images of STEREO/EUVI, SDO/AIA, and PROBA2/SWAP and could be implemented on white-light coronagraph images of STEREO/COR-1. CIISCO will find its application for VELC data-set as well as future coronagraphs observing the inner corona. The coronagraph observations suffer from gradient in intensity radially outwards due to decreasing density. The radial gradient is steeper in the inner corona observations. With the existing technology, no instrument has been devised to observe the coronal structures with high dynamic range matching that of human eye. To reduce the radial intensity variation in coronagraph images and study the dynamic structures such as CMEs we developed a Simple Radial Gradient Filter (SiRGraF). SiRGraF has been tested on high signal to noise ratio (SNR) coronagraph images of SOHO/LASCO and STEREO/COR2 and low SNR images of STEREO/COR1 and KCor. The algorithm turns out to be faster than existing ones when hundreds of images have to be processed for analysis. Finally a statistical study of small scale eruptions, plasmoids, associated with post-CME current sheet of September 10, 2017 has been carried out. We identified and tracked the plasmoids from inner to outer corona using EUV and white-light observations. We provided first observational evidence of a single power law for the width distribution of plasmoids. This study also brings out the kinematic properties of the plasmoids from inner to outer corona. We also identified the presence of accelerating sun-ward moving plasmoids which were predicted by magnetohydrodynamic (MHD) simulations but were unobserved earlier. We provided an empirical relation between the width and speed of the plasmoids for their evolution that could constrain the future studies and MHD simulations. To improve the understanding of such dynamics using the combination of imaging and spectroscopy will be one of the objectives of VELC.