CME

[This originally appeared as a UKSP science nugget] Coronal mass ejections (CMEs) are huge, episodic eruptions of solar plasma and magnetic field which travel through the solar corona and out into the heliosphere. At Earth, they drive the most severe geomagnetic storms and thus are the primary focus of space-weather forecasting. Using white-light imagers, individual CMEs can be tracked continuously from the low corona, through the solar wind, all the way to Earth [1] and beyond. Such observations show CMEs apparently bouncing off each other [2] and deflecting off other coronal and solar wind structures [3]. Thus it is tempting to think of a CME as a coherent structure; a single – perhaps even quasi-solid — body, playing out a game of solar billiards. Such structural coherence has two physical requirements. Firstly, coherence requires a restoring force which can (at least partially) resist deformation by external factors. E.g., A bubble is a coherent body as surface tension communicates external forces across the entirety...