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Invisibility of Solar Active Region Umbra-to-Umbra Coronal Loops: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal HeatingCoronal heating generally increases with increasing magnetic field strength: the EUV/X-ray corona in active regions is 10--100 times more luminous and 2--4 times hotter than that in quiet regions and coronal holes, which are heated to only about 1.5 MK, and have fields that are 10--100 times weaker than that in active regions. From a comparison of a nonlinear force-free model of the three-dimensional active region coronal field to observed extreme-ultraviolet loops, we find that (1) umbra-to-umbra coronal loops, despite being rooted in the strongest magnetic flux, are invisible, and (2) the brightest loops have one foot in an umbra or penumbra and the other foot in another sunspot's penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidence that magnetoconvection drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Our results from EUV observations and nonlinear force-free modeling of coronal magnetic field imply that, for any coronal loop on the Sun or on any other convective star, as long as the field can be braided by convection in at least one loop foot, the stronger the field in the loop, the stronger the coronal heating.
Document ID
20170011680
Acquisition Source
Marshall Space Flight Center
Document Type
Presentation
Authors
Tiwari, Sanjiv K.
(Lockheed Martin Solar and Astrophysical Laboratory Palo Alto, CA, United States)
Thalmann, Julia K.
(Graz Univ. Austria)
Panesar, Navdeep K.
(Universities Space Research Association Huntsville, AL, United States)
Moore, Ronald L.
(Alabama Univ. Huntsville, AL, United States)
Winebarger, Amy R.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Date Acquired
December 12, 2017
Publication Date
December 11, 2017
Subject Category
Solar Physics
Report/Patent Number
MSFC-E-DAA-TN50039
Meeting Information
Meeting: AGU Fall Meeting
Location: New Orleans, LA
Country: United States
Start Date: December 11, 2017
End Date: December 15, 2017
Sponsors: American Geophysical Union
Funding Number(s)
CONTRACT_GRANT: NNM11AA01A
CONTRACT_GRANT: NNX17AL21G
CONTRACT_GRANT: NNG09FA40C
CONTRACT_GRANT: FWF-P25383-N27
CONTRACT_GRANT: NNH15CO48B
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
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