Impulsive Acceleration of Coronal Mass Ejections. I. Statistics and Coronal Mass Ejection Source Region Characteristics

Abstract

We use high time cadence images acquired by the STEREO EUVI and COR instruments to study the evolution of coronal mass ejections (CMEs), from their initiation, through the impulsive acceleration to the propagation phase. For a set of 95 CMEs we derived detailed height, velocity and acceleration profiles and statistically analysed characteristic CME parameters: peak acceleration, peak velocity, acceleration duration, initiation height, height at peak velocity, height at peak acceleration and size of the CME source region. The CME peak accelerations derived range from 20 to 6800 m s −2 and are inversely correlated to the acceleration duration and to the height at peak acceleration. 74% of the events reach their peak acceleration at heights below 0.5 R ⊙ . CMEs which originate from compact sources low in the corona are more impulsive and reach higher peak accelerations at smaller heights. These findings can be explained by the Lorentz force, which drives the CME accelerations and decreases with height and CME size.

The Physical Processes of CME/ICME Evolution

“…When the slowly evolving structure reaches an unstable state (so called "loss of equilibrium" mechanism of Forbes and Isenberg 1991), the structure starts to accelerate, driven by some form of ideal MHD instabilities such as the kink or torus modes (e.g., and references therein Kliem 2003, 2005;Kliem and Török 2006;Démoulin and Aulanier 2010;Olmedo and Zhang 2010;Török et al 2010). Then follows the take-off stage, which is most often characterized by accelerations on the order of 100 m s −2 , and lasts for ∼ 1 h, so the majority of CMEs achieve velocities in the range 100-1000 km s −1 (e.g., Bein et al 2011;). However, sometimes the take-off phase is characterized by an extremely impulsive acceleration, achieving peak values on the order of 10 km s −2 , but lasting only for several minutes (e.g., Bein et al 2011).…”

“…Then follows the take-off stage, which is most often characterized by accelerations on the order of 100 m s −2 , and lasts for ∼ 1 h, so the majority of CMEs achieve velocities in the range 100-1000 km s −1 (e.g., Bein et al 2011;). However, sometimes the take-off phase is characterized by an extremely impulsive acceleration, achieving peak values on the order of 10 km s −2 , but lasting only for several minutes (e.g., Bein et al 2011). In such events the gradual pre-eruptive evolution is frequently not observed.…”

Global Energetics of Solar Flares. VI. Refined Energetics of Coronal Mass Ejections

“…Measurements of CME parameters from EUV dimming information started with the availability of solar EUV images, such as with the EUV Imaging Telescope (EIT) onboard SOHO since 1996 (e.g., Thompson et al 2000), the Extreme Ultra-Violet Imager (EUVI) onboard STEREO since 2006 (e.g., Bein et al 2011), and the Atmospheric Imager Assembly (AIA) onboard SDO since 2010 (e.g., Cheng et al 2012;Mason et al 2014;Kraaikamp and Verbeek 2015;Aschwanden 2016, Paper IV). Dimming regions were identified by areas of strong depletion in the EUV brightness, mapping out the apparent "footpoint" area of a CME, which is detected with a white-light coronagraph generally about an hour later (Thompson et al 2000).…”

“…Most CME studies focus on a single or on a small number of events, while statistical studies are rare. We identified about 60 studies that contain large statistics (≈ 10 2 − 10 5 events) of observed and physical CME parameters, such as the sizes and locations of CMEs (Hundhausen 1993;Bewsher et al 2008;Wang et al 2011), the CME speed, acceleration, mass, and energy (Moon et al 2002;Yurchyshyn et al 2005;Zhang and Dere 2006;Cheng et al 2010;Bein et al 2011;Joshi and Srivastava 2011;Gao et al 2011), and the associated flare hard X-ray fluxes, fluences, and durations (Yashiro et al 2006;Aarnio et al 2011). The most extensive statistics of CME parameters is provided in on-line catalogs of CME events detected with the white-light method, mostly from the Large- Angle and Spectrometric Coronagraph Experiment (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) (Brueckner et al 1995), such as the CDAW, Cactus, SEEDS, and CORIMP catalogs of CME events, but also from STEREO/COR2 (see web links in Section 4.1).…”

The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts

“…They are average speeds, not capturing, for example, the impulsive acceleration of CMEs close to the Sun (e.g. Bein et al 2011). In addition, the LCPF generally precedes the CME, meaning that the speeds are not measured simultaneously.…”