Abstract

<p>We studied 43 coronal dimming events associated with Earth-directed coronal mass ejections (CMEs) that were observed in quasi-quadrature by the SDO and STEREO satellites. We derived the properties of the dimmings as observed above the limb by STEREO EUVI, and compared them with the mass and speed of the associated CMEs. The unique satellite constellation allowed us to compare our findings with the results from Dissauer et al. (2018, 2019), who studied these events observed against the solar disk by SDO AIA. Such statistics is done for the first time and confirms the close relation between characteristic dimming and CME parameters for the off-limb viewpoint. We find that the dimming areas are typically larger for off-limb observations (mean value of 1.24±1.23×10<sup>11</sup> km<sup>2</sup> against 3.51±0.71×10<sup>10</sup> km<sup>2</sup> for on-disk), while the decrease in the total extreme ultraviolet intensity is similar (c=0.60±0.14). The off-limb dimming areas and brightnesses are strongly correlated with the CME mass (c=0.82±0.06 and 0.75±0.08), whereas the dimming area and brightness change rate correlate with the CME speed (c∼0.6). Our findings suggest that coronal dimmings have the potential to provide early estimates of the Earth-directed CMEs parameters, relevant for space weather forecasts, for satellite locations at both L1 and L5.</p>

Highlights

  • Coronal Mass Ejections (CMEs) are the most energetic and powerful eruptive phenomena on the Sun and the main drivers of space weather effects

  • We focus on 43 events in which coronal dimmings and their associated Earth-directed CMEs were observed off-limb by at least one of the two Solar Terrestrial Relations Observatory (STEREO) satellites. 39 of these events overlap with the event set from Dissauer et al (2018b, 2019) who studied the same dimmings as observed on-disk by the Atmospheric Imaging Assembly (AIA) instrument on-board NASA’s Solar Dynamics Observatory (SDO) satellite (Lemen et al 2012)

  • These events have been observed during a period where the STEREO s/c were in quasi-quadrature with spacecraft located along the Sun-Earth line, and the same dimming events have been studied in observations against the solar disk by the SDO/AIA instrument in Dissauer et al (2018b, 2019)

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Summary

Introduction

Coronal Mass Ejections (CMEs) are the most energetic and powerful eruptive phenomena on the Sun and the main drivers of space weather effects. Earth-directed CMEs are most difficult to measure using observations from instruments along the SunEarth line, due to strong projection effects (Burkepile et al 2004). In these cases, we mostly observe the CME’s expansion motion and not its propagation towards Earth. Depending on the position on their orbits around the Sun, the STEREO satellites provide us with the capability to observe Earth-directed CMEs from the side, including observations of their initiation and early evolution above the limb in Extreme-Ultraviolet (EUV) and coronagraph observations by the EUVI and COR instruments

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