The Brightness of Density Structures at Large Solar Elongation Angles: What is Being Observed by STEREO/SECCHI?

Abstract

We discuss features of coronal mass ejections (CMEs) that are specific to heliospheric observations at large elongation angles. Our analysis is focused on a series of two eruptions that occurred on 2007 January 24-25, which were tracked by the Heliospheric Imagers (HIs) onboard STEREO. Using a three-dimensional (3-D) magneto-hydrodynamic simulation of these ejections with the Space Weather Modeling Framework (SWMF), we illustrate how the combination of the 3-D nature of CMEs, solar rotation, and geometry associated with the Thomson sphere results in complex effects in the brightness observed by the HIs. Our results demonstrate that these effects make any in-depth analysis of CME observations without 3-D simulations challenging. In particular, the association of bright features seen by the HIs with fronts of CME-driven shocks is far from trivial. In this Letter, we argue that, on 2007 January 26, the HIs observed not only two CMEs, but also a dense corotating stream compressed by the CME-driven shocks.

5 pages, 2 figures, accepted for ApJ Letter

References in corpus (2)

• Three-Dimensional MHD Simulation of the 2003 October 28 Coronal Mass Ejection: Comparison with LASCO Coronagraph Observations
• Observational evidence of CMEs interacting in the inner heliosphere as inferred from MHD simulations

Cited by in corpus (5)

• Determining the azimuthal properties of coronal mass ejections from multi-spacecraft remote-sensing observations with stereo secchi
• Accuracy and Limitations of Fitting and Stereoscopic Methods to Determine the Direction of Coronal Mass Ejections from Heliospheric Imagers Observations
• Solar-Terrestrial Simulation in the STEREO Era: The January 24-25, 2007 Eruptions
• Numerical Modeling of Interplanetary Coronal Mass Ejections and Comparison with Heliospheric Images
• Using an Ellipsoid Model to Track and Predict the Evolution and Propagation of Coronal Mass Ejections