DIRECT RADIO PROBING AND INTERPRETATION OF THE SUN'S PLASMA DENSITY PROFILE

Abstract

The Sun's electron number density profile ne(r) is vital for solar physics but not well measured or understood within a few solar radii RS. Here, a new technique extracts ne(r) directly from coronal type III radio bursts for 40 ≤ f ≤ 180 MHz. Unexpectedly, wind-like regions with ne ∝ (r − RS)−2 are quite common below 2RS, and coronal type IIIs often have closely linear 1/f − t spectra. The profile ne ∝ (r − RS)−2 is consistent with the radio data and simulations and is interpreted in terms of conical flow from localized sources (e.g., UV funnels) close to the photosphere. It is consistent with solar wind acceleration occurring for 2 ≤ r/RS ≤ 10.