Coronal density

The electron density distribution in the corona is obtained, with the regular cadence of one hour, from LASCO/C2 images, between 2 and 6 solar radii and in coronal sectors 60-degree wide across the equator. The need to provide electron-density maps with the same frequency as the images from the “Sun now” module, requires to calculate the density using total-brightness data, and not the pB measurements, that are performed by LASCO only once per day.

We use a standard technique consisting in the inversion of the integral along the LOS of the total K-corona, which is due to the Thomson scattering of the solar disk radiation off coronal electrons (see van de Hulst 1950; Hayes et al. 2001). The K-corona brightness is derived from the total coronal brightness after subtraction of a model of the F-corona.