Séminaire: 3D electron density distributions in the solar corona during solar minima: assessment for more realistic solar wind modeling

The distribution of the magnetic field generated in the solar interior and connected into the solar wind influences most coronal phenomena including large-scale and slowly evolving coronal structures. Knowledge of the electron density distribution in the solar corona can serve as a tracer of the configuration of the coronal magnetic field, and provide constraints on the field configurations for coronal modeling as well as on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996-1997 and 2008-2010), devoid of Coronal Mass Ejections. We derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method, and compare the results between the two solar minima and with two magnetohydrodynamic models. First we confirm that the values of the density distribution in thermodynamic models are more realistic than in polytropic ones.} The tomography provides more accurate distributions in the polar regions, and we find that the density in tomographic and thermodynamic solutions varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers.  We deduce that tomography offers reliable density distributions in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how they are magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in-situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus.