The nascent fast solar wind observed by EIS onboard Hinode

TL;DR

This paper presents the first spectroscopic evidence of the early stages of the fast solar wind in a polar coronal hole, showing temperature-dependent upflows that originate in the transition region and expand into the corona.

Contribution

It provides new observational evidence of the nascent fast solar wind using Hinode/EIS data, highlighting temperature-dependent plasma outflows along open magnetic field lines.

Findings

Detection of blueshifted emission lines indicating upflows.

Upflows originate in the transition region and intensify with temperature.

Magnetic funnels guide the solar wind outflow.

Abstract

The origin of the solar wind is one of the most important unresolved prob- lems 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)=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.