Active region transition region loop populations and their relationship to the corona

TL;DR

This study uses high-resolution solar observations to identify two main types of active region loops with distinct heating and cooling behaviors, revealing their temperature evolution and dynamic properties.

Contribution

It provides new insights into the temperature-dependent populations of active region loops and their dynamic evolution, using Hinode/EIS data.

Findings

Identified two dominant loop populations: core multi-temperature and peripheral loops.

Core loops undergo continuous heating and cooling across 0.4-2.5 MK.

Peripheral loops evolve mainly within 0.4-1.3 MK.

Abstract

The relationships among coronal loop structures at different temperatures is not settled. Previous studies have suggested that coronal loops in the core of an active region are not seen cooling through lower temperatures and therefore are steadily heated. If loops were cooling, the transition region would be an ideal temperature regime to look for a signature of their evolution. The Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode provides monochromatic images of the solar transition region and corona at an unprecedented cadence and spatial resolution, making it an ideal instrument to shed light on this issue. Analysis of observations of active region 10978 taken in 2007 December 8 -- 19 indicates that there are two dominant loop populations in the active region: core multi-temperature loops that undergo a continuous process of heating and cooling in the full observed temperature range 0.4-2.5 MK and even higher as shown by the X-Ray Telescope (XRT); and peripheral loops which evolve mostly in the temperature range 0.4-1.3 MK. Loops at transition region temperatures can reach heights of 150 Mm in the corona above the limb and develop downflows with velocities in the range of 39-105 km/s.