Advancing in situ modeling of ICMEs: New techniques for new observations

Abstract

It is generally known that multispacecraft observations of interplanetary coronal mass ejections (ICMEs) are more likely to reveal their three‐dimensional structure than single‐spacecraft observations. The launch of STEREO in October 2006 has greatly increased the number of multipoint ICME studies, but the field is still in its infancy. To date, many studies still use flux rope models that rely on single track observations through a vast, multifaceted structure, which oversimplifies the problem and hinders interpretation of the large‐scale geometry. This oversimplification is especially problematic for multispacecraft ICME observations in which only one spacecraft observes a flux rope structure. To tackle these complex problems, we describe two new techniques and combine them to analyze two ICMEs observed at the twin STEREO spacecraft on 22–23 May 2007, when the spacecraft were separated by ∼ 9∘. We find a combination of non–force‐free flux rope multispacecraft modeling, together with a new non–flux rope ICME plasma flow deflection model, better constrains the large‐scale structure of these ICMEs. We also introduce a new spatial mapping technique that allows us to put multispacecraft observations and the new ICME model results in context with the convecting solar wind. What is distinctly different about this analysis is that it reveals aspects of ICME geometry and dynamics in a far more visually intuitive way than previously accomplished. In the case of the 22–23 May ICMEs, the analysis facilitates a more physical understanding of ICME large‐scale structure, the location and geometry of flux rope substructures within these ICMEs, and their dynamic interaction with the ambient solar wind.