The Kinematics of a Globally Propagating Disturbance in the Solar Corona

Abstract

The kinematics of a globally propagating disturbance (also known as an ``EIT wave") is discussed using Extreme UltraViolet Imager (EUVI) data Solar Terrestrial Relations Observatory (STEREO). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 A passband the disturbance shows a velocity peak of 238+/-20 kms-1 within ~28 minutes of its launch, varying in acceleration from 76 ms-2 to -102 ms-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ~1.6 MK. The 304 A emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 A passband the velocity varies significantly, peaking at 475+/-47 kms-1 within ~20 minutes of launch, with a variation in acceleration from 816 ms-2 to -413 ms-2. The high image cadence of the 171 A passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ~2 and ~10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.Comment: 4 pages 4 figure

Large-scale Globally Propagating Coronal Waves

“…This was first observed for a coronal EUV wave by Long et al (2008) and Veronig et al (2008), and studied in detail by Gopalswamy et al (2009). The reflected wave was clearly seen in difference images and in intensity profile stack plots (see Figure 30).…”

“…With STEREO/EUVI, wavefronts could be seen for the same event in all three of these channels (Long et al, 2008;Veronig et al, 2008), plus in 304Å images, where the fronts are comparatively faint and diffuse. These observations have confirmed earlier multiwavelength studies that clearly showed that coronal wave are multithermal phenomena.…”

“…The signatures seen at 304Å have been attributed to coronal emission of the Si xi line (303.32Å; ≈ 1.6 MK) rather than to chromospheric emission of the much cooler the He ii line ( ≈ 0.08 MK) that dominates this spectral channel (Long et al, 2008;). This interpretation is based on the morphological similarity of the 304Å wave with the signatures in the hotter coronal channels (cf.…”

“…rising and expanding loops that presumably represent the early CME (e.g., Long et al, 2008;Veronig et al, 2008;Kienreich et al, 2009;Veronig et al, 2010). The wavefronts then detach from the loops and propagate freely.…”

Large-scale Bright Fronts in the Solar Corona: A Review of “EIT waves”

“…The inset at bottom right shows the velocity as a function of time from Hα (crosses) and EIT (circles). Veronig et al 2008;Long et al 2008). Using two events observed in EIT 195Å supplemented by Hα images, Warmuth et al (2001) reported a non-linear velocity profile, implying a non-zero acceleration for the disturbance for at least the first ≤2000 s of the observations.…”