Heating and cooling of coronal loops observed by SDO

TL;DR

This study uses SDO observations to analyze coronal loop heating and cooling, providing evidence supporting nanoflares as a heating mechanism, while also revealing loop broadening not explained by current models.

Contribution

The paper offers observational validation of nanoflare heating in coronal loops and highlights the limitation of 1D models in explaining loop broadening.

Findings

Loops show rapid heating and cooling consistent with nanoflare predictions.

Loops become broader as they brighten, indicating multi-dimensional effects.

Observation supports nanoflare heating hypothesis in solar corona.

Abstract

Context: One of the most prominent processes suggested to heat the corona to well above 10^6 K builds on nanoflares, short bursts of energy dissipation. Aims: We compare observations to model predictions to test the validity of the nanoflare process. Methods: Using extreme UV data from AIA/SDO and HMI/SDO line-of-sight magnetograms we study the spatial and temporal evolution of a set of loops in active region AR 11850. Results: We find a transient brightening of loops in emission from Fe xviii forming at about 7.2 MK while at the same time these loops dim in emission from lower temperatures. This points to a fast heating of the loop that goes along with evaporation of material that we observe as apparent upward motions in the image sequence. After this initial phases lasting for some 10 min, the loops brighten in a sequence of AIA channels showing cooler and cooler plasma, indicating the cooling of the loops over a time scale of about one hour. A comparison to the predictions from a 1D loop model shows that this observation supports the nanoflare process in (almost) all aspects. In addition, our observations show that the loops get broader while getting brighter, which cannot be understood in a 1D model.