The radial speed‐expansion speed relation for Earth‐directed CMEs

Abstract

Earth‐directed coronal mass ejections (CMEs) are the main drivers of major geomagnetic storms. Therefore, a good estimate of the disturbance arrival time at Earth is required for space weather predictions. The STEREO and SOHO spacecraft were viewing the Sun in near quadrature during January 2010 to September 2012, providing a unique opportunity to study the radial speed (Vrad)‐expansion speed (Vexp) relationship of Earth‐directed CMEs. This relationship is useful in estimating the Vrad of Earth‐directed CMEs, when they are observed from Earth view only. We selected 19 Earth‐directed CMEs observed by the Large Angle and Spectrometric Coronagraph (LASCO)/C3 coronagraph on SOHO and the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)/COR2 coronagraph on STEREO during January 2010 to September 2012. We found that of the three tested geometric CME models the full ice‐cream cone model of the CME describes best the Vrad‐Vexp relationship, as suggested by earlier investigations. We also tested the prediction accuracy of the empirical shock arrival (ESA) model proposed by Gopalswamy et al. (2005a), while estimating the CME propagation speeds from the CME expansion speeds. If we use STEREO observations to estimate the CME width required to calculate the Vrad from the Vexp measurements, the mean absolute error (MAE) of the shock arrival times of the ESA model is 8.4 h. If the LASCO measurements are used to estimate the CME width, the MAE still remains below 17 h. Therefore, by using the simple Vrad‐Vexp relationship to estimate the Vrad of the Earth‐directed CMEs, the ESA model is able to predict the shock arrival times with accuracy comparable to most other more complex models.

Three-dimensional MHD simulation of the 2008 December 12 coronal mass ejection: from the Sun to Interplanetary space

“…So, the expansion speed will be higher for the higher magnetic fields magnitude in the CME (Riley & Crooker, 2004;Byrne et al, 2010). There are many authors investigated the empirical relationship between the radial speed and the expansion speed of CMEs (Lago et al, 2003;Gopalswamy et al, 2009Gopalswamy et al, , 2012Mäkelä et al, 2016). They found a high correlation between these two speeds.…”

Assessing the Projection Correction of Coronal Mass Ejection Speeds on Time‐of‐Arrival Prediction Performance Using the Effective Acceleration Model

“…All rights reserved. Xue et al, 2005;Makela et al, 2016 and references therein) because it seems to capture rather well the spherical shape of the 3-part CME. However, it leads to rather unrealistically high speed corrections for events close to the central meridian, which led us to question whether the assumption of a spherical front is valid for all CMEs.…”

Pursuing Forecasts of the Behavior and Arrival of Coronal Mass Ejections through Modeling and Observations

“…Examples of these are those by Gopalswamy et al (2001Gopalswamy et al ( , 2005, Wang et al (2002), Srivastava & Venkatakrishnan (2004), Xie et al (2006), andMichalek et al (2008). Other approaches rely on the concept of radial and expansion speed of CMEs (Schwenn et al 2005, Mäkelä et al 2016. Prediction techniques may for instance also profit from interplanetary scintillation information (e.g.…”