On the Variation in the Volumetric Evolution of CMEs from the Inner to Outer Corona

Abstract

Some of the major challenges faced in understanding the early evolution of coronal mass ejections (CMEs) are due to the limited observations in the inner corona (<3 Re) and the plane-of-sky measurements. In this work, we have thus extended the application of the Graduated Cylindrical Shell (GCS) model to inner coronal observations from the ground-based coronagraph K-Cor of the Mauna Loa Solar Observatory, along with the pairs of observations from COR-1 on board the Solar Terrestrial Relations Observatory. We study the rapid initial acceleration and width expansion phases of five CMEs in white light at the lower heights. We also study the evolution of the modeled volumes of these CMEs in the inner corona and report, for the first time, a power-law dependence of CME volume with distance from the Sun. We further find that the volumes of the ellipsoidal leading front and the conical legs follow different power laws, thus indicating differential volume expansion throughout a CME. The study also reveals two distinct power laws for the total volume evolution of CMEs in the inner and outer corona, thus suggesting different expansion mechanisms at these different heights. Besides aiding our current understanding of CME evolution, these results will also provide better constraints to CME initiation and propagation models. Also, given the loss of the STEREO-B (and hence COR-1B data) from 2016, the modified GCS model presented here will still enable stereoscopy in the inner corona for the 3D study of CMEs in white light.