DIRECT RADIO PROBING AND INTERPRETATION OF THE SUN’S DENSITY PROFILE

The Sun’s electron number density profile ne(r) is not well measured and understood from the Sun’s photosphere (r = RS) to the solar wind (say, r > 10 RS), despite its great importance for solar physics. A powerful new technique is developed and applied to extract ne(r) directly from the time-varying frequency of coronal type III radio bursts, for the first time. Unexpectedly, wind-like regions with ne = A (r - RS)-2 are common below 2RS, and coronal type III bursts often are almost linear in 1/f - t dynamic spectra. Indices lower and higher than 2 also occur, the former plausibly due to non-radial curved magnetic field lines. The profile ne = A (r - RS)-2 is consistent with the coronal radio data, type III simulations, and previous models based on eclipse and coronagraph observations. It gives a first physical basis for the previous models. A simple interpretation is in terms of conical flow from localized sources close to the photosphere, plausibly corresponding to UV funnels. The results also imply that solar wind acceleration occurs where 2 < r/RS < 10.