Solar Wind from Coronal Funnels and Transition Region Lyalpha
Using a newly developed gyrotropic solar wind model that extends continuously from the mid-chromosphere to 1 AU and that accounts for radiative losses in the transition region, we have studied the difference between the fast solar wind emanating from a funnel geometry and a ``traditional'' rapidly expanding wind. The main aim is to determine whether or not observations of the Lyalpha intensity in the low transition region can be reconciled with solar wind models. In a rapidly expanding geometry, we are not able to produce a Lyalpha intensity much higher than 1/10 of the observed values without creating a large pressure in the transition region and, as a result, a mass flux much higher than observed. In a funnel, on the other hand, we can easily obtain the observed Lyalpha intensity, while still having a wind solution in agreement with observations. The main reason for this is that the fast flow in the funnel causes hydrogen to be very far from ionization equilibrium, with the Lyalpha intensity coming from temperatures of about 5×10^4 K. At these elevated temperatures, the radiative loss is much more efficient. The results of this Letter support the idea that the solar wind originates from small coronal funnels.
Source at https://doi.org/10.1086/444497