On the origin of the fast solar wind in polar coronal funnels

Funnels are open magnetic structures connecting the chromosphere with the s olar corona (Axford & McKenzie 1997; Marsch & Tu 1997; Hackenberg et al. 19 99). We investigate the stationary plasma flow out of funnels with a flux-t ube model. The funnel area function is derived from an analytical 2-D magne tic field model. Since the funnel height is only approximately 15 Mm, the a rea function for greater heights is taken from the Banaszkiewicz et al. (19 98) coronal magnetic field model. Thus we obtain a realistic area function being valid into the upper corona. The plasma in the funnel is treated with two-fluid equations including radi ative losses, thermal conduction, electron-proton heat exchange, proton hea ting by cyclotron-damped Alfven waves and Alfven wave pressure. We adjust t he free parameters to the quantities measured in the lower solar corona (ap proximate to 100 000 km above the photosphere) by SUMER aboard SOHO (Wilhel m et al. 1998). The thereby obtained height profiles of the plasma properti es (e.g. density, electron and proton temperatures, flow speed) within the funnel are presented and compared with recent SUMER measurements.