Features of the Initial Stage of Formation of Fast Coronal Mass Ejection on February 25, 2014

Abstract

We have analyzed the fast coronal mass ejection (CME) that occurred on February 25, 2014. The analysis is based on images taken in the 131, 211, 304, and 1700 Å UV channels of the SDO/AIA instrument and from observations obtained in the Hα line (6562.8 Å) with the telescopes of the Teide and Big Bear Observatories.
 The February 25, 2014 CME is associated with the ejection and subsequent explosive expansion of the magnetic flux rope, which appeared near the solar surface presumably due to the tether-cutting magnetic reconnection.
 The impulse of full pressure (thermal plus magnetic) resulting from such an “explosion” acts on the overlying coronal arcades, causing them to merge and form an accelerated moving frontal structure of the CME. This pressure impulse also generates a blast collisional shock wave ahead of the CME, whose velocity decreases rapidly with distance. At large distances R>7R₀ (R₀ is the solar radius) from the center of the Sun in front of the CME, a shock wave of another type is formed — a “piston” collisional shock wave whose velocity varies little with distance.
 At R≥15R₀, there is a transition from a collisional to a collisionless shock wave.

Possible difference in the formation of coronal mass ejections of two types

“…The process develops similarly during the February 25, 2014 event as well [Eselevich, Eselevich, 2020].…”

“…Let us carry out a similar analysis for two limb CMEs of a different type, namely, the CMEs associated with eruptive prominences, or type 2 CMEs, using the August 24, 2014 and February 25, 2014 events, which have been analyzed in detail in [Eselevich et al, 2016;Eselevich, Eselevich, 2020] as an example. By an eruptive prominence is meant a magnetic flux rope with a core of cold (T<6000-10000 K) plasma, which was at rest above the photosphere prior to the event.…”

“…associated with an eruptive prominence. Since the essence of both type 2 CMEs is the same, and the events themselves have been analyzed in detail in [Eselevich et al, 2016;Eselevich, Eselevich, 2020], here we take a brief look only at the August 24, 2014 event to illustrate the differences and reasons for the classification into type 1 and type 2 CMEs.…”