[Loops] Time lag Analysis and Coronal Heating

[Viall-kepko, Nicholeen M. (GSFC-6710)]

Dear Loop Enthusiasts, 

We have a new paper extending our time lag analysis to 15 active regions. It was recently accepted to ApJ, and the online version can be found here: 
https://doi.org/10.3847/1538-4357/aa7137

Many of you are here in Palermo, and I look forward to answering any questions you have and discussing this paper while we are all together!

Title: A Survey of Nanoflare Properties in Active Regions Observed with the Solar Dynamics Observatory
Authors: Nicholeen M. Viall and James A. Klimchuk

Abstract:
In this paper, we examine 15 different active regions (ARs) observed with the Solar Dynamics Observatory and analyze their nanoflare properties. We have recently developed a technique that systematically identifies and measures plasma temperature dynamics by computing time lags between light curves. The time lag method tests whether the plasma is maintained at a steady temperature, or if it is dynamic, undergoing heating and cooling cycles. An important aspect of our technique is that it analyzes both observationally distinct coronal loops as well as the much more prevalent diffuse emission between them. We find that the widespread cooling reported previously for NOAA AR 11082 is a generic property of all ARs. The results are consistent with impulsive nanoflare heating followed by slower cooling. Only occasionally, however, is there full cooling from above 7 MK to well below 1 MK. More often, the plasma cools to approximately 1–2 MK before being reheated by another nanoflare. These same 15 ARs were first studied by Warren et al. We find that the degree of cooling is not well correlated with the reported slopes of the emission measure distribution. We also conclude that the Fe xviii emitting plasma that they measured is mostly in a state of cooling. These results support the idea that nanoflares have a distribution of energies and frequencies, with the average delay between successive events on an individual flux tube being comparable to the plasma cooling timescale.

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Nicholeen M. Viall  
Research Astrophysicist
Solar Physics Laboratory
Code 671
NASA Goddard Space Flight Center
Greenbelt, MD 20771
V: 301-286-4054
F: 301-286-7194
Nicholeen.M.Viall at nasa.gov