Evidence for Gently Sloping Plasma Density Profiles in the Deep Corona: Type III Observations

Here the blue line shows a model curved field line along which the particles stream as they excite a type III radio burst. This cartoon aims at supporting the view that radio type III bursts move out into the solar wind on a shallower gradient of density than that expected for the solar wind (density varying as r^-2 roughly). What the authors mean by "deep corona" in their title is that part close to the Sun, not the other way around. The competing simple law for density fall-off would be a hydrostatic law, which would be much steeper than what they see. There are possible geometrical interpretations of this, and of course there is probably a typical list of "plausible assumptions" involved, but nevertheless this seems to be another step towards the use of fast electrons as a remote-sensing tool for the corona.