title: The unresolved fine structure resolved: IRIS observations of the solar transition region.
abstract: The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long-standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low-lying loops or loop segments at transition-region temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a long-standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.
authors.affiliation: Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway. viggoh@astro.uio.no.
authors.forename: V
authors.initials: V
authors.lastname: Hansteen
authors.affiliation: Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway. Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: B
authors.initials: B
authors.lastname: De Pontieu
authors.affiliation: Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway.
authors.forename: M
authors.initials: M
authors.lastname: Carlsson
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: J
authors.initials: J
authors.lastname: Lemen
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: A
authors.initials: A
authors.lastname: Title
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: P
authors.initials: P
authors.lastname: Boerner
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: N
authors.initials: N
authors.lastname: Hurlburt
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Tarbell
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Wuelser
authors.affiliation: Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway.
authors.forename: T M D
authors.initials: TM
authors.lastname: Pereira
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: De Luca
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: L
authors.initials: L
authors.lastname: Golub
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: S
authors.initials: S
authors.lastname: McKillop
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: K
authors.initials: K
authors.lastname: Reeves
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: S
authors.initials: S
authors.lastname: Saar
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: P
authors.initials: P
authors.lastname: Testa
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: H
authors.initials: H
authors.lastname: Tian
authors.affiliation: Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA.
authors.forename: C
authors.initials: C
authors.lastname: Kankelborg
authors.affiliation: Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA.
authors.forename: S
authors.initials: S
authors.lastname: Jaeggli
authors.affiliation: Bay Area Environmental Research Institute, 596 1st Street West, Sonoma, CA 95476, USA. Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: L
authors.initials: L
authors.lastname: Kleint
authors.affiliation: Bay Area Environmental Research Institute, 596 1st Street West, Sonoma, CA 95476, USA. Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: J
authors.initials: J
authors.lastname: Martínez-Sykora