Numerical modeling of interplanetary coronal mass ejections and comparison with heliospheric images

Interplanetary coronal mass ejections (ICMEs) have complex magnetic and density structures, which are the result of their interaction with the structured solar wind and with previous eruptions. ICMEs are revealed by in situ measurements and in the past five years, through remote-sensing observations by heliospheric imagers. However, to understand and analyze these observations often requires the use of numerical modeling. It is because no instruments can yet provide a simple view of ICMEs in two or three dimensions. Numerical simulations can be used to determine the origin of a complex ejecta observed near Earth, or to analyze the origin, speed and extent of density structures observed remotely. Here, we review and discuss recent efforts to use numerical simulations of ICMEs to investigate the magnetic topology, density structure, energetics and kinematics of ICMEs in the interplanetary space. After reviewing existing numerical models of ICMEs, we first focus on numerical modeling in support of the SMEI and STEREO observations. 3-D simulations can help determining the origins of the fronts observed by SECCHI and SMEI, especially for complex events such as the January 24–25, 2007 CMEs. They can also be used to test different methods to derive ICME properties from remote observations, to predict and explain observational effects, and to understand the deceleration and deformation of ICMEs. In the last part, we focus on the numerical investigation of non-magnetic cloud ejecta. We discuss how simulations are crucial to understand the formation of non-twisted ejecta and the formation of complex ejecta due to the interaction of multiple ICMEs. ► Simulations are used in support of observations of ICMEs, such as these done by STEREO. ► Simulations are used to test analysis methods for in situ and remote observations of ICMEs. ► Simulations can reveal the physical processes during ICME-ICME interaction. ► Ejecta with low twist but large writhe may be mistaken for twisted flux rope.