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The Deflection of the Two Interacting Coronal Mass Ejections of 2010 May 23-24 as Revealed by Combined In situ Measurements and Heliospheric Imaging  

No Lugaz   Submitted: 2012-09-24 09:29

In 2010 May 23-24, SDO observed the launch of two successive coronal mass ejections (CMEs), which were subsequently tracked by the SECCHI suite onboard STEREO. Using the COR2 coronagraphs and the heliospheric imagers (HIs), the initial direction of both CMEs is determined to be slightly west of the Sun-Earth line. We derive the CME kinematics, including the evolution of the CME expansion until 0.4 AU. We find that, during the interaction, the second CME decelerates from a speed above 500 km s-1 to 380 km s-1 the speed of the leading edge of the first CME. STEREO observes a complex structure composed of two different bright tracks in HI2-A but only one bright track in HI2-B. In situ measurements from Wind show an ''isolated'' ICME, with the geometry of a flux rope preceded by a shock. Measurements in the sheath are consistent with draping around the transient. By combining remote-sensing and in situ measurements, we determine that this event shows a clear instance of deflection of two CMEs after their collision, and we estimate the deflection of the first CME to be about 10 degrees towards the Sun-Earth line. The arrival time, arrival speed and radius at Earth of the first CME are best predicted from remote-sensing observations taken before the collision of the CMEs. Due to the over-expansion of the CME after the collision, there are few, if any, signs of interaction in in situ measurements. This study illustrates that complex interactions during the Sun-to-Earth propagation may not be revealed by in situ measurements alone.

Authors: N. Lugaz, C. J. Farrugia, J. A. Davies, C. Möstl, C. J. Davis, I. I. Roussev, M. Temmer
Projects: STEREO,Wind

Publication Status: accepted to Astrophysical Journal
Last Modified: 2012-09-24 11:12
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Deriving the radial distances of wide coronal mass ejections from elongation measurements in the heliosphere - Application to CME-CME interaction  

No Lugaz   Submitted: 2009-09-09 21:07

We present general considerations regarding the derivation of the radial distances of coronal mass ejections (CMEs) from elongation angle measurements such as those provided by SECCHI and SMEI, focusing on measurements in the Heliospheric Imager 2 (HI-2) field of view (i.e. past 0.3 AU). This study is based on a three-dimensional (3-D) magneto-hydrodynamics (MHD) simulation of two CMEs observed by SECCHI on January 24-27, 2007. Having a 3-D simulation with synthetic HI images, we are able to compare the two basic methods used to derive CME positions from elongation angles, the so-called ''Point-P'' and ''Fixed-Phi'' approximations. We confirm, following similar works, that both methods, while valid in the most inner heliosphere, yield increasingly large errors in HI-2 field of view for fast and wide CMEs. Using a simple model of a CME as an expanding self-similar sphere, we derive an analytical relationship between elongation angles and radial distances for wide CMEs. This relationship is simply the harmonic mean of the ''Point-P'' and ''Fixed-Phi'' approximations and it is aimed at complementing 3-D fitting of CMEs by cone models or flux rope shapes. It proves better at getting the kinematics of the simulated CME right when we compare the results of our line-of-sights to the MHD simulation. Based on this approximation, we re-analyze the J-maps (time-elongation maps) in January 26-27, 2007 and present the first observational evidence that the merging of CMEs is associated with a momentum exchange from the faster ejection to the slower one due to the propagation of the shock wave associated with the fast eruption through the slow eruption.

Authors: N. Lugaz, A. Vourlidas, I. I. Roussev
Projects: STEREO

Publication Status: Annales Geophysicae (accepted)
Last Modified: 2009-09-10 08:14
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Solar-Terrestrial Simulation in the STEREO Era: The January 24-25, 2007 Eruptions  

No Lugaz   Submitted: 2009-09-09 21:06

We present general considerations regarding the derivation of the radial distances of coronal mass ejections (CMEs) from elongation angle measurements such as those provided by SECCHI and SMEI, focusing on measurements in the Heliospheric Imager 2 (HI-2) field of view (i.e. past 0.3 AU). This study is based on a three-dimensional (3-D) magneto-hydrodynamics (MHD) simulation of two CMEs observed by SECCHI on January 24-27, 2007. Having a 3-D simulation with synthetic HI images, we are able to compare the two basic methods used to derive CME positions from elongation angles, the so-called ''Point-P'' and ''Fixed-Phi'' approximations. We confirm, following similar works, that both methods, while valid in the most inner heliosphere, yield increasingly large errors in HI-2 field of view for fast and wide CMEs. Using a simple model of a CME as an expanding self-similar sphere, we derive an analytical relationship between elongation angles and radial distances for wide CMEs. This relationship is simply the harmonic mean of the ''Point-P'' and ''Fixed-Phi'' approximations and it is aimed at complementing 3-D fitting of CMEs by cone models or flux rope shapes. It proves better at getting the kinematics of the simulated CME right when we compare the results of our line-of-sights to the MHD simulation. Based on this approximation, we re-analyze the J-maps (time-elongation maps) in January 26-27, 2007 and present the first observational evidence that the merging of CMEs is associated with a momentum exchange from the faster ejection to the slower one due to the propagation of the shock wave associated with the fast eruption through the slow eruption.

Authors: N. Lugaz, A. Vourlidas, I. I. Roussev
Projects: STEREO

Publication Status: Annales Geophysicae (accepted)
Last Modified: 2009-09-10 08:15
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Solar-Terrestrial Simulation in the STEREO Era: The January 24-25, 2007 Eruptions  

No Lugaz   Submitted: 2009-03-13 18:26

The SECCHI instruments aboard the recently launched STEREO spacecraft enable for the first time the continuous tracking of coronal mass ejections (CMEs) from the Sun to 1 AU. We analyze line-of-sight observa- tions of the January 24-25, 2007 CMEs and fill the 20-hour gap in SECCHI coverage in January 25 by performing a numerical simulation using a three- dimensional magneto-hydrodynamic (MHD) code, the Space Weather Modeling Framework (SWMF). We show how the observations reflect the interaction of the two successive CMEs with each other and with the structured solar wind. We make detailed comparison between the observations and synthetic images from our model, including time-elongation maps for several position angles. Having numerical simulations to disentangle observational from physical effects, we are able to study the three-dimensional nature of the ejections and their evolution in the inner heliosphere. This study reflects the start of a new era where, on one hand, models of CME propagation and interaction can be fully tested by using heliospheric observations and, on the other hand, observations can be better interpreted by using global numerical models.

Authors: N. Lugaz, A. Vourlidas, I. I. Roussev, H. Morgan
Projects: None

Publication Status: Solar Physics (recommended for acceptance)
Last Modified: 2009-03-14 14:26
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Abstracts by Author
The Deflection of the Two Interacting Coronal Mass Ejections of 2010 May 23-24 as Revealed by Combined In situ Measurements and Heliospheric Imaging
Deriving the radial distances of wide coronal mass ejections from elongation measurements in the heliosphere - Application to CME-CME interaction
Solar-Terrestrial Simulation in the STEREO Era: The January 24-25, 2007 Eruptions
Solar-Terrestrial Simulation in the STEREO Era: The January 24-25, 2007 Eruptions

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