Panel a: electron density vs. heliocentric height for the active region electron density models of Zucca et al. (2014), Baumbach-Allen (Aschwanden 2005), and Newkirk (1961, 1967). Panel b: plasma frequency vs. heliocentric height for each density model. An example of how we estimated the source height of an S-burst with a frequency of ∼19 MHz is shown. Panel c: distribution of measured source electron velocities. Panel d: source electron velocity distribution according to the model of Melnik et al. (2010) when using a value of θ = 90°. Panel e: magnetic field strengths predicted by Melnik et al. (2010) at each of the source height estimates according to our data. In this case, a value of θ = 90° is used to allow for a source velocity of 0.07 c as implied by our observations.