Speaker
Description
Coronal mass ejections (CMEs) have been measured in situ since the 1970s with missions such as Helios, Voyager, IMP-8, Voyager. Over the past 30 years, we have now gained routine measurements by Wind and ACE at the Sun-Earth L1, in the inner heliosphere by STEREO, and in the innermost heliosphere and corona by Solar Orbiter and Parker Solar Probe. With 1000s of measurements from heliocentric distances of a fraction of an AU to several tens of AU, a better understanding of the average properties of CMEs and how it varies with both solar cycle and distance can be obtained. Additionally, the passage of STEREO-A by the Sun-Earth line during the maximum of solar cycle 25 combined with L1 and Solar Orbiter measurements, reveal for the first time the typical angular width of CMEs, and how their properties vary longitudinally. Such measurements are key to better constrain inputs of mid-term heliospheric evolution and to better understand space weather and solar wind-magnetospheric coupling.
I will summarize results from recent studies showing that the axial and poloidal components of the CME magnetic field decrease similarly with distance, and discuss how it must be reconcile by theoretical and fitting model. I will also show that CME properties for long-term heliospheric evolution models cannot be taken from remote observations, as those only capture the CME density and speed. Multi-spacecraft measurements of CMEs reveal conclusively that the magnetic ejecta of CMEs is narrower than previously thought and that CMEs have a complex combination of coherence and lack of coherence within their cross-section.