Understanding our capabilities in observing and modelling Coronal Mass Ejections

Coronal Mass Ejections (CMEs) are large-scale eruptions of plasma and magnetic fields from the Sun. They are considered to be the main drivers of strong space weather events at Earth and their arrival time and associated shocks are one of the key aspects of space weather. Multiple models have been developed over the past decades to be able to predict the propagation of CMEs in the interplanetary space and their arrival time at Earth. Such models require input from observations, which can be used to fit the CME to an appropriate structure. The forecasting of CME arrival has proven to be exceedingly challenging. One of the major setbacks is the uncertainty of the CME observational input. When determining input parameters for CME propagation models, it is common procedure to derive kinematic parameters from remote-sensing data. The resulting parameters can be used as inputs for the CME propagation models to obtain an arrival prediction time of the CME f.e. at Earth. However, when fitting the CME structure to obtain the needed parameters for simulations, different geometric structures and also different parts of the CME structure can be fitted. These aspects, together with the fact that 3D reconstructions strongly depend on the subjectivity and judgement of the scientist performing them, may lead to uncertainties in the fitted parameters. Up to now, no large study has tried to map these uncertainties and to evaluate how they affect the modelling of CMEs. We will discuss these limits in the scope of the CME input analysis that is performed by the ISSI Bern team on "Understanding Our Capabilities In Observing and Modelling Coronal Mass Ejections".