Diagnostics of the Coronal Hole and the adjacent Quiet Sun by The Hinode/EUV Imaging Spectrometer (EIS)

TL;DR

This study uses Hinode/EIS spectroscopic diagnostics to compare a coronal hole and adjacent quiet Sun, identifying coronal funnels, plasma flows, and non-thermal velocities to understand solar wind origins and wave dissipation.

Contribution

It provides new spectral signatures and diagnostics for identifying coronal funnels and characterizing plasma flows in coronal holes and quiet Sun regions.

Findings

Coronal funnels are identified by excess width regions and high density concentrations.

Non-thermal velocities are higher in coronal holes, indicating sources of fast solar wind.

Flow patterns show down-flows in lower atmosphere and up-flows in the corona, with wave dissipation signatures.

Abstract

A comparison between a Coronal Hole (CH) and the adjacent Quiet-Sun (QS) has been performed using spectroscopic diagnostics of Hinode/ the EUV Imaging Spectrometer (EIS). Coronal funnels play an important role in the formation and propagation of the nascent fast solar wind. Applying Gaussian fitting procedures to the observed line profiles, Doppler velocity, intensity, line width (FWHM) and electron density have been estimated over CH and adjacent QS region of a North Polar Coronal Hole (NPCH). The aim of this study is to identify the coronal funnels based on spectral signatures. Excess width regions (excess FWHM above a threshold level) have been identified in QS and CH. The plasma flow inversion (average red-shifts changing to blue-shifts at a specific height) in CH and excess width regions of QS take place at ~ 5.01$\times$10$^{5}$ K. Furthermore, high density concentration in excess width regions of QS provides an indication that these regions are the footprints of coronal funnels. We have also found that non-thermal velocities of CH are higher in comparison to QS confirming that the CHs are the source regions of fast solar wind. Doppler and non-thermal velocities as recorded by different temperature lines have been also compared with previously published results. As we go from lower to upper solar atmosphere, down-flows are dominated in lower atmosphere while coronal lines are dominated by up-flows with a maximum value of ~ 10-12 km s$^{-1}$ in QS. Non-thermal velocity increases first but after Log T$_{e}$ = 5.47 it decreases further in QS. This trend can be interpreted as a signature of the dissipation of Alfv\'en waves, while increasing trend as reported earlier may attribute to the signature of the growth of Alfv\'en waves at lower heights. Predominance of occurrence of nano-flares around O {\sc vi} formation temperature could also explain non-thermal velocity trend.