Global Variation of the Coronal Electron Density with Solar Cycle and its Comparison with 3D MHD Modeling

Abstract:

The temporal variations of the total or integrated radiance of the K-corona were found to be correlated with solar activity (or sunspot) cycle in some previous studies. In this study, we address the question on how the global electron content of the corona varies with the solar cycle by analyzing STEREO/COR1 pB images over a period from 2007 (near solar minimum of Solar Cycle 23) to 2014 (near solar maximum of Solar Cycle 24). We reconstruct the 3D coronal density by using a spherically symmetric polynomial approximation (SSPA) method on the COR1-A and -B data gathered over half a solar rotation. We find that the total mass of the corona within 1.5-3.7 solar radius reaches a minimum at solar minimum near 2009 and then stays stable until 2010 when the solar activity starts to again increase. The coronal mass is seen to increase by a factor ≈2 from solar minimum to solar maximum while exhibiting strong variations. We explore the cause of this variation by exploring its relationship with the temporal variation of total magnetic flux of the close fields using PFSS extrapolations to SOHO/MDI and SDO/MHI magnetic field data. In addition, for some selected solar rotations we compare the reconstructed 3D density structures with density structures predicted by the Corona Heliosphere (CORHEL) and Magnetohydrodynamics Around the Sphere (MAS) models in the Community Coordinated Modeling Center (CCMC) to understand the physical mechanism that determines the distribution and evolution of the coronal densities.