Understanding the Physical Nature of Coronal “EIT Waves”

Abstract

For almost 20 years the physical nature of globally propagating waves in the solar corona (commonly called “EIT waves”) has been controversial and subject to debate. Additional theories have been proposed over the years to explain observations that did not agree with the originally proposed fast-mode wave interpretation. However, the incompatibility of observations made using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory with the fast-mode wave interpretation was challenged by differing viewpoints from the twin Solar Terrestrial Relations Observatory spacecraft and data with higher spatial and temporal resolution from the Solar Dynamics Observatory. In this article, we reexamine the theories proposed to explain EIT waves to identify measurable properties and behaviours that can be compared to current and future observations. Most of us conclude that the so-called EIT waves are best described as fast-mode large-amplitude waves or shocks that are initially driven by the impulsive expansion of an erupting coronal mass ejection in the low corona.

A Statistical Analysis of the Solar Phenomena Associated with Global EUV Waves

“…However, this value was slightly lower than the intercept found by Muhr et al (2014) using STEREO/EUVI observations. The consistency between the results presented here and by Warmuth (2010), Warmuth and Mann (2011) and Muhr et al (2014) indicates that these features are large-amplitude events as outlined by Long et al (2017).…”

“…Since then, the general consensus has been reached that they are initially driven by the rapid lateral expansion of the erupting CME in the low corona; a conclusion strongly supported by the SDO observations reported by Patsourakos, Vourlidas, and Stenborg (2010). A detailed discussion of the predictions made by the different theories and how recent observations support this conclusion may be found in the recent paper by Long et al (2017).…”

“…The result of this impulsive lateral expansion is best observed as a global EUV wave (cf. Long et al, 2017). Despite this, there is no clear relationship between global EUV waves and SEP events, with most previous work tending to focus on individual case-study events (e.g.…”

“…Recent work comparing the predictions made by each of these theories with observations suggests that they are best described as large-amplitude waves initially driven by the rapid lateral expansion of a CME in the low corona, before propagating freely (cf. Long et al, 2017).…”

Three-dimensional Reconstructions of Extreme-ultraviolet Wave Front Heights and Their Influence on Wave Kinematics

“…In the meantime, there seems to be a consensus reached that EUV waves are large-amplitude fast-mode MHD waves or shocks (cf. the recent reviews by Patsourakos & Vourlidas 2012;Liu & Ofman 2014;Warmuth 2015;Long et al 2017). The disturbance is most likely initiated by the impulsive lateral expansion of the CME flanks, which temporarily act as a piston-type driver (e.g., Vršnak & Cliver 2008).…”