Forecasting the Structure and Orientation of Earthbound Coronal Mass Ejections

Coronal Mass Ejections (CMEs) are the key drivers of strong to extreme space weather storms at the Earth that can have drastic consequences for technological systems in space and on ground. The ability of a CME to drive geomagnetic disturbances depends crucially on the magnetic structure of the embedded flux rope, which is thus essential to predict. The current capabilities in forecasting in advance (at least half a day before) the geoeffectiveness of a given CME is however severely hampered by the lack of remote-sensing measurements of the magnetic field in the corona and adequate tools to predict how CMEs deform, rotate, and deflect during their travel through the coronal and interplanetary space as they interact with the ambient solar wind and other CMEs. These problems can lead not only to overestimation or underestimation of the severity of a storm, but also to forecasting misses and false alarms that are particularly difficult for the end-users. In this paper, we discuss the current status and future challenges and prospects related to forecasting of the magnetic structure and orientation of CMEs. We focus both on observational- and modeling-based (first principle and semiempirical) approaches and discuss the space- and ground-based observations that would be the most optimal for making accurate space weather predictions. We also cover the gaps in our current understanding related to the formation and eruption of the CME flux rope and physical processes that govern its evolution in the variable ambient solar wind background that complicate the forecasting. Plain Language Summary Coronal Mass Ejections (CMEs) are gigantic magnetized plasma clouds that are frequently expelled from the Sun. Practically all strong and extreme space weather disturbances in the near-Earth space environment are caused by CMEs that propagate in a few days from the Sun to the Earth. Space weather disturbances are related to various harmful effects to modern technology both in space and on ground which can lead to substantial economic losses. Forecasting the CME properties at least half a day before their impact on Earth is thus essential for our society. Our ability to provide accurate predictions of space weather consequences of CMEs is however currently quite modest. The key challenges are related to observational and modeling limitations, and complex evolution CMEs may experience as they propagate from Sun to Earth. This paper discusses the current status and future prospect in forecasting key CME properties using both observations and simulations.