Interactions Between Coronal Mass Ejections Viewed in Coordinated Imaging and in Situ Observations

Abstract

The successive coronal mass ejections (CMEs) from 2010 July 30 -August 1 present us the first opportunity to study CME-CME interactions with unprecedented heliospheric imaging and in situ observations from multiple vantage points. We describe two cases of CME interactions: merging of two CMEs launched close in time and overtaking of a preceding CME by a shock wave. The first two CMEs on August 1 interact close to the Sun and form a merged front, which then overtakes the July 30 CME near 1 AU, as revealed by wideangle imaging observations. Connections between imaging observations and in situ signatures at 1 AU suggest that the merged front is a shock wave, followed by two ejecta observed at Wind which seem to have already merged. In situ measurements show that the CME from July 30 is being overtaken by the shock at 1 AU and is significantly compressed, accelerated and heated. The interaction between the preceding ejecta and shock also results in variations in the shock strength and structure on a global scale, as shown by widely separated in situ measurements from Wind and STEREO B. These results indicate important implications of CME-CME interactions for shock propagation, particle acceleration and space weather forecasting.

The 2010 August 1 Type Ii Burst: A Cme-Cme Interaction and Its Radio and White-Light Manifestations

“…between STEREO-B and Wind ), which is about the same angular separation derived by the direction-finding technique. The obtained propagation direction is in agreement with finding of Temmer et al (2011) and Liu et al (2011).…”

“…The period 2010 July 31 to August 2 was characterized by increased solar activity, exhibiting small flares, filament eruptions and coronal mass ejections (Schrijver and Title 2011;Temmer et al 2011;Liu et al 2011). Of particular interest here is the time during which two CMEs (one slow(CME1), erupted at 02:00UT and one fast(CME2), erupted at 07:00UT) interacted with each other, resulting in a low frequency type II radio burst observed on 2010 August 1 at about 09:00 UT).…”

“…The average speed of the fast CME, derived from Cor2 observations is ∼1138 km s −1 with a liftoff time of ∼07:48 UT from the Sun. The liftoff time of the slow CME was calculated to be 02:48 UT with an average propagation velocity of 730 km s −1 in Cor2 Liu et al 2011). Unfortunately, the STEREO-B Cor1 and HI1 had a data gap of about 18 hours starting at 9:20 UT, which restricted our analysis.…”

A Numerical Study of Long-Range Magnetic Impacts During Coronal Mass Ejections

“…When propagating into the solar wind, sympathetic events are prone to CME-CME interaction (e.g., Lugaz et al 2008Lugaz et al , 2012Liu et al 2014b). Such interactions may significantly modify the structure of the CME-driven shock wave and the properties of the interplanetary CME (ICME), and therefore affect the potential of space weather effects (e.g., Liu et al 2012Liu et al , 2014aMöstl et al 2012). Interactions between CMEs from the same AR have often been discussed (e.g., Lugaz et al 2005bLugaz et al , 2007Lugaz et al , 2013Xiong et al 2006), but CMEs can be spatially extended and those from distant regions may also interact, adding complexity to solar wind data (e.g., Temmer et al 2012).…”

Using Coordinated Observations in Polarized White Light and Faraday Rotation to Probe the Spatial Position and Magnetic Field of an Interplanetary Sheath

“…At an interaction site, both the plasma density and magnetic field would be compressed, leading to enhanced signatures in both WL and FR observations. For example, the interaction between two CMEs was manifested as a very bright arc in WL images (e.g., Harrison et al 2012;Liu et al 2012;Temmer et al 2012). Different types of interactions would likely result in different WL radiance signatures; in fact, through a single interaction, the corresponding radiance pattern could evolve.…”