Statistics of coronal dimmings associated with coronal mass ejections. II. Relationship between coronal dimmings and their associated CMEs

TL;DR

This study statistically analyzes 62 coronal dimming events associated with Earth-directed CMEs, revealing correlations between dimming properties and CME dynamics, and providing insights into the physical mechanisms driving CMEs.

Contribution

It offers a comprehensive statistical analysis of coronal dimmings and their relationship with CME properties, highlighting new correlations and physical insights.

Findings

Dimming area and magnetic flux correlate with CME mass.

Dimming intensity correlates with CME peak velocity.

Magnetic field strength in dimmings relates to CME acceleration.

Abstract

We present a statistical study of 62 coronal dimming events associated with Earth-directed CMEs during the quasi-quadrature period of STEREO and SDO. This unique setting allows us to study both phenomena in great detail and compare characteristic quantities statistically. Coronal dimmings are observed on-disk by SDO/AIA and HMI, while the CME kinematics during the impulsive acceleration phase is studied close to the limb with STEREO/EUVI and COR, minimizing projection effects. The dimming area, its total unsigned magnetic flux and its total brightness, reflecting properties of the total dimming region at its final extent, show the highest correlations with the CME mass ($c\sim0.6-0.7$). Their corresponding time derivatives, describing the dynamics of the dimming evolution, show the strongest correlations with the CME peak velocity ($c\sim 0.6$). The highest correlation of $c=0.68\pm0.08$ is found with the mean intensity of dimmings, indicating that the lower the CME starts in the corona, the faster it propagates. No significant correlation between dimming parameters and the CME acceleration was found. However, for events where high-cadence STEREO observations were available, the mean unsigned magnetic field density in the dimming regions tends to be positively correlated with the CME peak acceleration ($c=0.42\pm0.20$). This suggests that stronger magnetic fields result in higher Lorentz forces providing stronger driving force for the CME acceleration. Specific coronal dimming parameters correlate with both, CME and flare quantities providing further evidence for the flare-CME feedback relationship. For events in which the CME occurs together with a flare, coronal dimmings statistically reflect the properties of both phenomena.