Sun-to-earth propagation of the 2015 June 21 coronal mass ejection revealed by optical, EUV, and radio observations

Abstract

We investigate the propagation of the 2015 June 21 CME-driven shock as revealed by the type II bursts at metric and longer wavelengths and coronagraph observations. The CME was associated with the second largest geomagnetic storm of solar cycle 24 and a large solar energetic particle (SEP) event. The eruption consisted of two M-class flares, with the first one being confined, with no metric or interplanetary radio bursts. However, there was intense microwave burst, indicating accelerated particles injected toward the Sun. The second flare was eruptive that resulted in a halo CME. The CME was deflected primarily by an equatorial coronal hole that resulted in the modification of the intensity profile of the associated SEP event and the duration of the CME at Earth. The interplanetary type II burst was particularly intense and was visible from the corona all the way to the vicinity of the Wind spacecraft with fundamental-harmonic structure. We computed the shock speed using the type II drift rates at various heliocentric distances and obtained information on the evolution of the shock that matched coronagraph observations near the Sun and in-situ observations near Earth. The depth of the geomagnetic storm is consistent with the 1-AU speed of the CME and the magnitude of the southward component.One of the controversies in this event is the low speed of the CME (~330 km s -1 ) in the outer corona (~26 solar radii) assumed by Piersanti et al. (2017), based on measurements provided by the CORIMP automatic CME catalog. With such low speed, these authors estimated the shock arrival at Earth on June 25, while the shock arrived on June 22, about 39.5 hours after the eruption. In fact, the shock and interplanetary (IP) CME (ICME) speeds were much higher at 1 AU (>700 km s -1 ). This is one of the motivations to clarify the CME kinematics near the Sun because we know that CMEs that survive into the IP medium to reach Earth are generally fast and wide (Gopalswamy et al. 2010a). We show that the shock speed is consistently high throughout the inner heliosphere and the deceleration is typical of most CMEs reported in the literature. We also use multiple methods to infer the true speed of the shock from white-light and radio data. In particular, we use IP type II radio burst data to derive the shock speed in the inner heliosphere. The CME and the shock are tightly coupled, so it is not possible to have a 330 km s -1 CME driving a >1000 km s -1 shock.The solar source of the CME has not received much attention in the literature (Liu et al. 2015;Piersanti et al. 2017). Soft-X-ray observations show two M-class flares in quick succession from the same active region. We examine the spatial distribution of the flare emission to show that it is different during the two flares: the first flare (X-ray class M2.0) was confined (no mass motion), while the second one (M2.6) was eruptive and hence associated with the CME in question.Another motivation stems from the confusion regarding the nature and extent of the IP counterpart of the 2015 Ju...

An Observationally Constrained Analytical Model for Predicting the Magnetic Field Vectors of Interplanetary Coronal Mass Ejections at 1 au

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