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

Funnels are open magnetic structures connecting the chromosphere with the solar corona (Axford & McKenzie 1997; Marsch & Tu 1997; Hackenberg et al. 1999). We investigate the stationary plasma flow out of funnels with a flux-tube model. The funnel area function is derived from an analytical 2-D magnetic field model. Since the funnel height is only approximately 15 Mm, the area function for greater heights is taken from the Banaszkiewicz et al. (1998) 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 radiative losses, thermal conduction, electronproton heat exchange, proton heating by cyclotron-damped Alfvén waves and Alfvén wave pressure. We adjust the free parameters to the quantities measured in the lower solar corona (≈ 100 000 km above the photosphere) by SUMER aboard SOHO (Wilhelm et al. 1998). The thereby obtained height profiles of the plasma properties (e.g. density, electron and proton temperatures, flow speed) within the funnel are presented and compared with recent SUMER measurements.