[Loops] New paper on the transition region as observed with SDO/AIA
VIALL-KEPKO, NICHOLEEN M. (GSFC-6710)
nicholeen.m.viall at nasa.gov
Fri Jan 16 13:10:05 MST 2015
Dear Colleagues,
We have just published a new paper: Viall, N. M. & Klimchuk, J. A., 'The Transition Region Response to a Coronal Nanoflare: Forward Modeling and Observations in SDO/AIA', 2015, ApJ, 799, 58.
It can be found here: http://stacks.iop.org/0004-637X/799/58
Abstract: The 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.
Cheers,
Nicki
***************************
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
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