EGU2020-11425
https://doi.org/10.5194/egusphere-egu2020-11425
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evolution of the Alfvén Mach number associated with a coronal mass ejection shock

Ciara Maguire1,2, Eoin Carley1,2, Joseph McCauley1, and Peter Gallagher1,2
Ciara Maguire et al.
  • 1School of Physics, Trinity College Dublin, Dublin, Ireland (cmaguir4@tcd.ie)
  • 2School of Cosmic Physics, Dublin Institute for Advanced Studies, Dublin, Ireland

The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfvén Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfvén speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet (EUV) by the Solar Ultraviolet Imager (SUVI) on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph (LASCO) on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array (I-LOFAR). We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA was in the range 1.4-2.4 at a heliocentric distance of 1.6 R. The emission ceased when the CME nose reached 2.4 R, despite an increasing Alfvén Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.

How to cite: Maguire, C., Carley, E., McCauley, J., and Gallagher, P.: Evolution of the Alfvén Mach number associated with a coronal mass ejection shock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11425, https://doi.org/10.5194/egusphere-egu2020-11425, 2020

Displays

Display file