English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The Sun regularly produces large-scale eruptive events, such as coronal massejections (CMEs) that can drive shock waves through the solar corona. Suchshocks can result in electron acceleration and subsequent radio emission in theform of a type II radio burst. However, the early-phase evolution of shockproperties and its relationship to type II burst evolution is still subject toinvestigation. Here we study the evolution of a CME-driven shock by comparingthree commonly used methods of calculating the Alfv\'en Mach number ($M_A$),namely: shock geometry, a comparison of CME speed to a model of the coronalAlfv\'en speed, and the type II band-splitting method. We applied the threemethods to the 2017 September 2 event, focusing on the shock wave observed inextreme ultraviolet (EUV) by the Solar Ultraviolet Imager (SUVI) on boardGOES-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 LowFrequency Array (I-LOFAR). We show that the three different methods ofestimating shock $M_A$ yield consistent results and provide a means of relatingshock property evolution to the type II emission duration. The type II radioemission emerged from near the nose of the CME when $M_A$ was in the range1.4-2.4 at a heliocentric distance of $\sim$1.6 $R_\odot$. The emission ceasedwhen the CME nose reached $\sim$2.4 $R_\odot$, despite an increasing Alfv\'enMach number (up to 4). We suggest the radio emission cessation is due to thelack of quasi-perpendicular geometry at this altitude, which inhibits efficientelectron acceleration and subsequent radio emission.

Evolution of the Alfv\'en Mach number associated with a coronal mass ejection shock