Speaker
Description
Summary
Coronal mass ejections (CMEs) are important drivers of the space weather. Therefore, most studies focus on the fastest and thus most dangerous ICME events. However, the `typical' or average CME propagates at a velocity only slightly higher than the slow solar wind speed and, especially during solar minimum, fast CMEs are in fact rather exceptional. Yet, also the magnetic clouds associated to the slower CMEs are recognized to be able to cause significant geomagnetic disturbances.
We will discuss 2.5D (axi-symmetric) magnetic flux rope models and 2.5D and 3D self-consistent magnetohydrodynamics (MHD) simulation models for the onset of CMEs under solar minimum conditions, and for their interaction with coronal streamers and subsequent evolution up to 1AU. The flux-rope models take into account the inner magnetic structure of the CMEs and quantify its effect on their IP evolution and interaction with the background solar wind, including erosion (due to magnetic reconnection), deformation (due to slow wind interaction), deflection (due to neighboring streamer interaction), etc. The self-similar CMEs are initiated by magnetic flux emergence/cancellation and/or by shearing the magnetic foot points of a magnetic arcade which is positioned above or below the equatorial plane and embedded in a larger helmet streamer. The overlying magnetic streamer field then deflects the CMEs towards the equator, and the deflection path is dependent on the driving velocity. The core of the CME, created during the onset process, contains a magnetic flux rope and the synthetic white light images often show the typical three-part CME structure. Observations are used to constrain the models by providing initial and boundary conditions. These solar observations, as well as the resulting characteristic plasma parameters they produce at 1AU compared to (ACE) observations, provide excellent tools to validate the models. These advanced CME models are now being integrated in the new inner heliosphere model Euhforia (the ‘European ENLIL’ models) we developed. They are validated by comparison with ENLIL results and with observational data of a selection of well-documented cases. The current state-of-the-art will be reviewed.
