Doppler shift of the quiet region measured by meridional scans with the EUV Imaging Spectrometer onboard Hinode

TL;DR

This study measures Doppler shifts in the solar quiet region's transition layer across a range of coronal temperatures using Hinode's EUV spectrometer, revealing temperature-dependent flow patterns.

Contribution

It provides detailed Doppler shift measurements over a wide temperature range, improving understanding of plasma motions in the solar transition region.

Findings

Doppler shifts are near zero below log T=6.0.

Blueshifts increase with temperature above log T=6.0.

Maximum blueshift observed is -6.3 km/s at log T=6.25.

Abstract

Spatially averaged (> 50'') EUV spectral lines in the transition region of solar quiet regions are known to be redshifted. Because the mechanism underlying this phenomenon is unclear, we require additional physical information on the lower corona for limiting the theoretical models. To acquire this information, we measured the Doppler shifts over a wide coronal temperature range (log T[K]=5.7--6.3) using the spectroscopic data taken by the Hinode EUV Imaging Spectrometer. By analyzing the data over the center-to-limb variations covering the meridian from the south to the north pole, we successfully measured the velocity to an accuracy of 3 km/s. Below log T[K] = 6.0, the Doppler shifts of the emission lines were almost zero with an error of 1--3 km/s; above this temperature, they were blueshifted with a gradually increasing magnitude, reaching - 6.3 +/- 2.1 km/s at log T[K]=6.25.