What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models

TL;DR

This study uses 3D STEREO observations to analyze EUV waves, providing evidence that supports their interpretation as fast-mode MHD waves triggered by CME-related loop expansion.

Contribution

First detailed 3D analysis of EUV waves with STEREO data, clarifying their nature and supporting the fast-mode wave interpretation over pseudo-wave models.

Findings

Supports the fast-mode MHD wave interpretation of EUV waves.

Indicates EUV waves are triggered by CME-associated loop expansion.

Provides the first detailed 3D observational analysis of EUV waves.

Abstract

One of the major discoveries of the Extreme ultraviolet Imaging Telescope (EIT) on SOHO were intensity enhancements propagating over a large fraction of the solar surface. The physical origin(s) of the so-called `EIT' waves is still strongly debated. They are considered to be either wave (primarily fast-mode MHD waves) or non-wave (pseudo-wave) interpretations. The difficulty in understanding the nature of EUV waves lies with the limitations of the EIT observations which have been used almost exclusively for their study. Their limitations are largely overcome by the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes provide high cadence, simultaneous multi-temperature coverage, and two well-separated viewpoints. We present here the first detailed analysis of an EUV wave observed by the EUVI disk imagers on December 07, 2007 when the STEREO spacecraft separation was $\approx 45^\circ$. Both a small flare and a CME were associated with the wave cadence, and single temperature and viewpoint coverage. These limitations are largely overcome by the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes provide high cadence, simultaneous multi-temperature coverage, and two well-separated viewpoints. Our findings give significant support for a fast-mode interpretation of EUV waves and indicate that they are probably triggered by the rapid expansion of the loops associated with the CME.