On the propagation of a geoeffective coronal mass ejection during 15–17 March 2015

Abstract

The largest geomagnetic storm so far, called 2015 St. Patrick's Day event, in the solar cycle 24 was produced by a fast coronal mass ejection (CME) originating on 15 March 2015. It was an initially west‐oriented CME and expected to only cause a weak geomagnetic disturbance. Why did this CME finally cause such a large geomagnetic storm? We try to find some clues by investigating its propagation from the Sun to 1 AU. First, we reconstruct the CME's kinematic properties in the corona from the SOHO and Solar Dynamics Observatory imaging data with the aid of the graduated cylindrical shell model. It is suggested that the CME propagated to the west ∼33°±10° away from the Sun‐Earth line with a speed of about 817 km s−1 before leaving the field of view of the SOHO/Large Angle and Spectrometric Coronagraph (LASCO) C3 camera. A magnetic cloud (MC) corresponding to this CME was measured in situ by the Wind spacecraft 2 days after the CME left LASCO's field of view. By applying two MC reconstruction methods, we infer the configuration of the MC as well as some kinematic information, which implies that the CME possibly experienced an eastward deflection on its way to 1 AU. However, due to the lack of observations from the STEREO spacecraft, the CME's kinematic evolution in interplanetary space is not clear. In order to fill this gap, we utilize numerical MHD simulation, drag‐based CME propagation model (DBM) and the model for CME deflection in interplanetary space (DIPS) to recover the propagation process, especially the trajectory, of the CME from 30RS to 1 AU under the constraints of the derived CME's kinematics near the Sun and at 1 AU. It is suggested that the trajectory of the CME was deflected toward the Earth by about 12°, consistent with the implication from the MC reconstruction at 1 AU. This eastward deflection probably contributed to the CME's unexpected geoeffectiveness by pushing the center of the initially west‐oriented CME closer to the Earth.

The Physical Processes of CME/ICME Evolution

“…studied the role of the CME mass, and found that in the range of distances covered by LASCO, the drag affects more strongly the propagation of light CMEs, and inferred that the Lorentz force is usually stronger in more massive events. and employed DBM to investigate how the CME-CME interaction affects the kinematics, whereas Wang et al (2016b) used it to infer the degree of deflection of a CME/ICME event. and Vrš-nak et al (2010Vrš-nak et al ( , 2014 compared the DBM and ENLIL ICME arrival-time predictions, and found that results of the two models to be similar accurate.…”

The 17 March 2015 storm: the associated magnetic flux rope structure and the storm development

“…The foregoing studies Kataoka et al 2015;Liu et al 2015;Cho et al 2016;Wang et al 2016) agree that a halo CME associated with a C9.1 flare which started at 01:15 UT on 15 March in AR 12297 (S22W25) was the solar source event of the MC. The general agreement comes from the fact that the above CME is the most prominent event and satisfies the consideration about the transit time from the Sun to 1 AU.…”

“…Four different ideas have been proposed for the MC boundaries by recent studies. They are: (i) 17/13:00-18/09:00 , (ii) 17/11:00-17/23:10 (Cho et al 2016), (iii) 17/13:05-17/23:20 Wang et al 2016), and (iv) two MCs, 17/09:00-17/18:00 and 17/18:00-18/17:00 . (Note that time intervals indicated above for selection by Gopalswamy et al (2015) and Kataoka et al (2015) are different from those in their original paper, because their corresponding times were taken from OMNI data, in which time is shifted for the solar wind transit from the observing satellite to the nose of Earth's bow shock.)…”

“…The 17 March 2015 geomagnetic storm is the largest in Solar Cycle 24 so far with minimum Dst of −223 nT and has stimulated many research activities (Kamide and Kusano 2015;Kataoka et al 2015;Liu et al 2015;Cho et al 2016;Wang et al 2016). The large geomagnetic storm was somewhat surprising, and space weather agencies worldwide failed to predict that such a severe storm would occur (Kamide and Kusano 2015;Kataoka et al 2015, Wang et al 2016.…”

“…The large geomagnetic storm was somewhat surprising, and space weather agencies worldwide failed to predict that such a severe storm would occur (Kamide and Kusano 2015;Kataoka et al 2015, Wang et al 2016. Thus, the prior concern was mechanisms having caused such an intense storm.…”