Coronal mass ejections (CMEs) are among the most dramatic events in the solar system, where coronal plasma and magnetic fields are explosively released into space. A full characterization of the coronal and interplanetary evolution of CMEs—and of their internal magnetic configuration—is one of the most pressing issues in space science. Two or more CMEs can collide during their journey away from the Sun, giving rise to even more complex structures that can potentially enhance space weather effects at Earth. CME–CME interaction events have been observed in remote-sensing imagery as well as in in-situ measurements, however, due to the sparse nature of available observations, many open questions remain. This project will address this issue through magnetohydrodynamic (MHD) simulations. The project supports an early career woman PI and undergraduate student researchers.<br/><br/>This project is a detailed investigation into the dynamics and consequences of CME–CME interaction aimed at addressing the following Science Questions: (1) Can we identify characteristic CME–CME interaction signatures that are common to most events and can be used as proxies for interaction occurrence? (2) Is it possible to determine an overall, global structure for CME–CME interaction events, or is every in-situ observation only sampling local properties? (3) Is there a combination of properties of the “original” CMEs relative to one another that leads to maximum geoeffectiveness? The Science Questions will be addressed via analyses of a series of MHD simulations based on idealized configurations, which will model different CME–CME interaction scenarios and properties of the resulting structures. The work will lay the groundwork for comprehensive understanding of CME–CME interaction processes in the inner heliosphere, and its results will be applicable to future in-situ analyses of real events.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.