DEM analysis of the 6 September 2011 large-scale coronal wave

¹ University of Graz, Institute of Physics, Universitätsplatz 5, 8010 Graz, Austria
² University of Graz, Kanzelhöhe Observatory for Solar and Environmental Research, Kanzelhöhe 19, 9521 Treffen, Austria
³ NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 12 March 2026
Accepted: 17 June 2026

Abstract

Context. Large-scale coronal waves are globally propagating intensity enhancements in extreme-ultraviolet (EUV) and soft X-ray (SXR) observations, in association with solar flares and coronal mass ejections (CMEs). They are interpreted as low-coronal signatures of a large-amplitude fast magnetosonic wave. On 6 September 2011, a fast (v ≈ 1000 km s⁻¹) large-scale coronal wave accompanied an eruptive X2.1 class flare. A notable feature of this event was the temporary disappearance of a segment of the wave front in EUV channels sensitive to quiet-Sun plasma, while the same structure remained visible in higher temperature channels.

Aims. We analyse the plasma properties associated with this large-scale coronal wave and quantify its impact on the local plasma as it passed through the corona. We aim to determine whether the temperature increase at the wave front can be explained solely by a compressive wave, and how the observed spatial variability relates to the plasma temperature distribution.

Methods. We evaluate plasma parameters at multiple locations along the wave front and across its propagation path. We apply differential emission measure (DEM) diagnostics to SDO/AIA EUV observations to derive local density, temperature, emission measure (EM), and DEM distributions, and examine their temporal evolution during the wave passage.

Results. The wave passage causes increases of 6–8% in density and 10–18% in temperature. While the density increase is comparable to earlier reports, the temperature increase exceeds expectations. This indicates that the temperature enhancement cannot be explained by compressional adiabatic heating alone, and instead suggests the presence of additional heating mechanisms, such as magnetic reconnection or wave mode conversion. During the temporary disappearance of the wave, the plasma parameters at the wave front increase, but with a strong spatial variability, with density increases as low as 1% and as high as 10%. The DEM distribution shows that the initial temperature in the affected area is notably higher than typical quiet-Sun regions (T¯ ≳ 1.7 MK), which allows plasma to be heated beyond the peak response of the AIA 193 and 211 Å channels. We conclude that the apparent temporary disappearance of the wave front is primarily due to the combined effects in the intensity of the CME-associated coronal dimming following the wave and the wave itself, with heating further reducing its detectability in channels sensitive to quiet-Sun temperatures.