Forecasting the Magnetic Structure of Earth-Bound CMEs

Abstract:

Coronal mass ejections (CMEs) are the main drivers of the strongest space weather disturbances in the near-Earth environment and they have thus been at the centre of space weather forecasting efforts for several decades. However, our capability to provide long-lead time predictions (at least half-a-day in advance) of the severity of the geomagnetic disturbances driven by CMEs remains rather modest. The knowledge of the magnetic field structure of Earth-bound CMEs is the key missing element in improving long-lead time space weather forecasts. Realistic information on the magnetic field of the CME at the time of the eruption is crucial for providing the first estimate of how strong the associated space weather effects are expected to be, and in particular as the accuracy of both first-principle space weather models (e.g, ENLIL and EUHFORIA) and semi-empirical models is directly influenced by the information input to the models. This talk discusses the key issues in measuring and estimating the magnetic field of CMEs in the corona and summarizes key existing efforts to obtain information on the intrinsic magnetic properties of CMEs, in particular those based on data-driven modelling and using indirect observational proxies. We then present results of a study where we explore the potential of nonlinear force-free field (NLFFF) extrapolation and time-dependent magnetofrictional modelling (TMFM) together with a semi-empirical Sun-to-Earth propagation method for providing estimates of the intrinsic magnetic structure of a CME of June 2012 that impacted Earth. This event had the largest magnetic field magnitudes observed with a CME flux rope in the near-Earth solar wind during Solar Cycle 24.