The origin of the solar wind is one of the most important unresolved problems in space and solar physics .
We report here the first spectroscopic signatures of the nascent fast solar wind on the basis of observations made by the EUV Imaging Spectrometer ( EIS ) on Hinode in a polar coronal hole , in which patches of blueshift are clearly present on dopplergrams of coronal emission lines with a formation temperature of \lg ( T / K ) \geq 6.0 .
The corresponding upflow is associated with open field lines in the coronal hole , and seems to start in the solar transition region and becomes more prominent with increasing temperature .
This temperature-dependent plasma outflow is interpreted as evidence of the nascent fast solar wind in the polar coronal hole .
The patches with significant upflows are still isolated in the upper transition region but merge in the corona , in agreement with the scenario of solar wind outflow being guided by expanding magnetic funnels .