Solar Corona Electron Densities from VLBI and GIM Data

Abstract

The electron density of the solar corona can be determined by multi-frequency radio measurements, e.g. to spacecraft during superior solar conjunctions. Recently, also Very Long Baseline Interferometry (VLBI) has been successfully used to estimate coronal electron densities. The greatest challenge was to separate the dispersive effects of the solar corona and the Earth’s ionosphere. Here, we developed and applied another approach including global ionospheric maps (GIM) to eliminate the effect of the ionosphere. By using such an external data set, an independent validation of the previous results is possible. The models of the electron density derived by these two approaches agree well: the electron density at the Sun’s surface is calculated as (1. 24 ± 0. 42) × 1012 m−3 (VLBI only) and (1. 31 ± 0. 51) × 1012 m−3 (VLBI + GIM). The results are compared to external information about indicators of solar activity (e.g. Sunspot numbers), coronagraph images as well as to models of the electron density determined by measurements to spacecraft.