Review and test of funnel shape geometries in solar wind acceleration

Abstract

The origin and heating of the solar wind is still a puzzle. We review in this study the idea that the solar wind originates in coronal funnels. We place emphasis on the fast solar wind. This study provides primarily a historic overview over the development of the idea of funnel expansion. We present examples of recent solar wind studies that investigate the funnel geometry. These studies include both static and time dependent reconnection geometries. The time dependent reconnection geometry that we present and evaluate in more detail is He et al. 2008. They present their model in order to explain why blue and red shift of the spectral lines Si II, C IV and Ne VIII can be seen in the same flow tubes on the sun. We have found some of the strengths and weaknesses with this model by comparing the models results to observations and to contemporary papers that treat the same ions. We have found that the model results fit relatively well to observed Doppler shifts (velocities), but that the model ignores the physical mechanism below 5*10^6 m that transports the heavy ions to that height, and it does not fully explain the choices of initial conditions, in particular why the mass input occurs exactly at 5*10^6 m. These challenges with this model may be important to take into account when developing future models of funnels.