Temperature and Differential Emission Measure Profiles in Turbulent Solar Active Region Loops

TL;DR

This paper investigates how different scattering mechanisms affect temperature profiles and emission measures in solar active region loops, revealing significant deviations from classical models and explaining observed low-temperature emission excess.

Contribution

It introduces a combined collisional and turbulent scattering model for coronal loops, revising existing scaling laws and explaining low-temperature emission features.

Findings

Turbulent scattering significantly alters temperature profiles.

Revised scaling laws better match observations.

Flatter temperature gradients increase low-temperature emission.

Abstract

We examine the temperature structure of static coronal active region loops in regimes where thermal conductive transport is driven by Coulomb collisions, by turbulent scattering, or by a combination of the two. (In the last case collisional scattering dominates the heat transport at lower levels in the loop where temperatures are low and densities are high, while turbulent scattering dominates the heat transport at higher temperatures/lower densities.) Temperature profiles and their corresponding differential emission measure distributions are calculated and compared to observations, and earlier scaling laws relating the loop apex temperature and volumetric heating rate to the loop length and pressure are revisited. Results reveal very substantial changes, compared to the wholly collision-dominated case, to both the loop scaling laws and the temperature/density profiles along the loop. They also show that the well-known excess of differential emission measure at relatively low temperatures in the loop may be a consequence of for by the flatter temperature gradients (and so increased amount of material within a specified temperature range) that results from the predominance of turbulent scattering in the upper regions of the loop.