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Invisibility of Solar Active Region Umbra-to-Umbra Coronal Loops: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal Heating
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Author and Affiliation:
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)
Abstract: Coronal 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.
Publication Date: Dec 11, 2017
Document ID:
20170011680
(Acquired Dec 13, 2017)
Subject Category: SOLAR PHYSICS
Report/Patent Number: MSFC-E-DAA-TN50039
Document Type: Oral/Visual Presentation
Meeting Information: AGU Fall Meeting; 11-15 Dec. 2017; New Orleans, LA; United States
Meeting Sponsor: American Geophysical Union; Washington, DC, United States
Contract/Grant/Task Num: NNH15CO48B; NNG09FA40C; FWF-P25383-N27; NNX17AL21G; NNM11AA01A
Financial Sponsor: NASA Marshall Space Flight Center; Huntsville, AL, United States
Organization Source: NASA Marshall Space Flight Center; Huntsville, AL, United States
Description: 1p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Portions of the document may include copyright protected material
NASA Terms: CORONAL LOOPS; EXTREME ULTRAVIOLET RADIATION; SOLAR ACTIVITY; SOLAR CONVECTION (ASTRONOMY); SOLAR CORONA; SOLAR MAGNETIC FIELD; STELLAR CORONAS; UMBRAS; BRIGHTNESS; CORONAL HOLES; MAGNETIC FLUX; SOLAR HEATING; SUNSPOTS; X RAY TELESCOPES
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