Heating and cooling of coronal loops observed by SDO

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.

9 pages, 7 figures, accepted by A&A

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• On-disk solar coronal condensations facilitated by magnetic reconnection between open and closed magnetic structures
• Signatures of the non-Maxwellian $\kappa$-distributions in optically thin line spectra. II. Synthetic Fe XVII--XVIII X-ray coronal spectra and predictions for the Marshall Grazing-Incidence X-ray Spectrometer (MaGIXS)
• Magnetic reconnection between loops accelerated by a nearby filament eruption
• An ultra-long and quite thin coronal loop without significant expansion
• Plasma injection into a solar coronal loop
• Formation of a solar filament by magnetic reconnection and coronal condensation
• Revisiting the formation mechanism for coronal rain from previous studies
• Morphological evidence for nanoflares heating warm loops in the solar corona
• Heating of quiescent coronal loops caused by nearby eruptions observed with the Solar Dynamics Observatory and the Solar Upper Transition Region Imager
• Temperature Analysis of Flaring (AR11283) and non-Flaring (AR12194) Coronal Loops