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The Transition Region Response to a Coronal Nanoflare: Forward Modeling and Observations in SDO/AIAThe corona and transition region (TR) are fundamentally coupled through the processes of thermal conduction and mass exchange. It is not possible to understand one without the other. Yet the temperature-dependent emissions from the two locations behave quite differently in the aftermath of an impulsive heating event such as a coronal nanoflare. Whereas the corona cools sequentially, emitting first at higher temperatures and then at lower temperatures, the TR is multithermal and the emission at all temperatures responds in unison. We have previously applied the automated time lag technique of Viall & Klimchuk to disk observations of an active region (AR) made by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. Lines of sight passing through coronal plasma show clear evidence for post-nanoflare cooling, while lines of sight intersecting the TR footpoints of coronal strands show zero time lag. In this paper, we use the EBTEL hydrodynamics code to demonstrate that this is precisely the expected behavior when the corona is heated by nanoflares. We also apply the time lag technique for the first time to off-limb observations of an AR. Since TR emission is not present above the limb, the occurrence of zero time lags is greatly diminished, supporting the conclusion that zero time lags measured on the disk are due to TR plasma. Lastly, we show that the "coronal" channels in AIA can be dominated by bright TR emission. When defined in a physically meaningful way, the TR reaches a temperature of roughly 60% the peak temperature in a flux tube. The TR resulting from impulsive heating can extend to 3 MK and higher, well within the range of the "coronal" AIA channels.
Document ID
20160005859
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Viall-Kepko, Nicholeen M.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Klimchuk, James A.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
May 5, 2016
Publication Date
January 20, 2015
Publication Information
Publication: The Astrophysical Journal
Publisher: IOP Science
Volume: 799
Issue: 1
ISSN: ?0004-637X
e-ISSN: 1538-4357
Subject Category
Solar Physics
Fluid Mechanics And Thermodynamics
Report/Patent Number
GSFC-E-DAA-TN31884
Distribution Limits
Public
Copyright
Other
Keywords
Sun: corona
sun: transition region

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