[Loops] new loops paper

[Klimchuk, James A. (GSFC-6710)]

Dear loops friends,

I hope you are well. You might be interested in a new paper just accepted by ApJ:  https://arxiv.org/abs/2007.15085.

Stay safe,
Jim

                                                                       Cross Sections of Coronal Loop Flux Tubes

                                                                                          James A. Klimchuk
                                                                             NASA Goddard Space Flight Center

                                                                                           Craig E. DeForest
                                                                                 Southwest Research Institute

                                                                                                 Abstract
            Coronal loops reveal crucial information about the nature of both coronal magnetic fields and coronal heating. The shape of the corresponding flux tube cross section and how it varies with position are especially important properties. They are a direct indication of the expansion of the field and of the cross-field spatial distribution of the heating. We have studied 20 loops using high spatial resolution observations from the first flight of the Hi-C rocket experiment, measuring the intensity and width as a function of position along the loop axis. We find that intensity and width tend to either be uncorrelated or to have a direct dependence, such that they increase or decrease together. This implies that the flux tube cross sections are approximately circular under the assumptions that the tubes have non-negligible twist and that the plasma emissivity is approximately uniform along the magnetic field. The shape need not be a perfect circle and the emissivity need not be uniform within the cross section, but sub-resolution patches of emission must be distributed quasi-uniformly within an envelope that has an aspect ratio of order unity. This raises questions about the suggestion that flux tubes expand with height, but primarily in the line-of-sight direction so that the corresponding (relatively noticeable) loops appear to have roughly uniform width, a long-standing puzzle. It also casts doubt on the idea that most loops correspond to simple warped sheets, although we leave open the possibility of more complex manifold structures.



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James A. Klimchuk

NASA Goddard Space Flight Center

Solar Physics Lab, Code 671

Bldg. 21, Rm. 158

Greenbelt, MD  20771

USA



Phone:  1-301-286-9060<tel:%28301%29%20286-9060>

Fax:      1-301-286-7194<tel:%28301%29%20286-7194>

E-mail:  James.A.Klimchuk at nasa.gov<mailto:James.A.Klimchuk at nasa.gov>

Homepage:  http://science.gsfc.nasa.gov/sed/bio/james.a.klimchuk<http://science.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iPhonebookId=15844>



No endorsement by NASA is implied for any correspondence related to my official role in professional organizations.



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