Hinode/EIS measurements of Abundances in Solar Active Region Outflows

Peripheral outflows appear to be a common feature of active regions, and may be a significant source of the slow speed solar wind. Spectral line profiles from the Hinode EUV Imaging Spectrometer (EIS) show that the bulk outflows reach speeds of ~50km/s with a much faster component reaching hundreds of km/s. I will review recent measurements of the elemental composition of the outflows obtained by EIS, with particular attention paid to AR 10978 that was observed as it crossed the solar disk in December 2007. EIS measurements show that the temperature distribution of the outflows is dominated by coronal emission, and that plasma with a slow wind-like composition flowed from the edge of AR 10978 for at least five days. Furthermore, when the outflow from the Western side was favorably oriented in the Earth direction, the composition was found to match the value measured a few days later by ACE/SWICS. The composition of the high speed component of the outflows was also found to be similar to that of the slow speed wind, implying that it may also be a contributor. Observations and models indicate that it takes time for plasma to evolve to the enhanced composition typical of the slow wind, suggesting that the material in the outflows is trapped on closed loops before escaping, perhaps by interchange reconnection. The results, therefore, also identify the high speed component of the plasma as having a coronal origin. A significant constraint on the mechanisms that drive the outflows.