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An ab Initio Approach to Solar Coronal Loops
Stockholm University, Faculty of Science, Department of Astronomy.
2005 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 618, no 2, 1031-1038 p.Article in journal (Refereed) Published
Abstract [en]

Data from recent numerical simulations of the solar corona and transition region are analyzed, and the magnetic field connections between the low corona and the photosphere are found to be close to those of a potential field. The field line-to-field line displacements follow a power-law distribution with typical displacements of just a few Mm. Three loops visible in simulated TRACE filters are analyzed in detail and found to have significantly different heating rates and distributions thereof, one of them showing a small-scale heating event. The dynamical structure is complicated, even though all the loops are visible in a single filter along most of their lengths. The loops are nonstatic and are in the process of evolving into loops with very different characteristics. Differential emission measure (DEM) curves along one of the loops illustrate that DEM curves have to be treated carefully if physical characteristics are to be extracted.

Place, publisher, year, edition, pages
The American Astronomical Society , 2005. Vol. 618, no 2, 1031-1038 p.
Keyword [en]
MHD; Sun: corona; Sun: magnetic fields
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-23513DOI: 10.1086/426064OAI: diva2:192437
Part of urn:nbn:se:su:diva-32Available from: 2004-02-04 Created: 2004-02-04 Last updated: 2010-09-15Bibliographically approved
In thesis
1. The coronal heating problem
Open this publication in new window or tab >>The coronal heating problem
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The heating of the solar corona has been investigated during four of decades and several mechanisms able to produce heating have been proposed. It has until now not been possible to produce quantitative estimates that would establish any of these heating mechanism as the most important in the solar corona. In order to investigate which heating mechanism is the most important, a more detailed approach is needed.

In this thesis, the heating problem is approached ”ab initio”, using well observed facts and including realistic physics in a 3D magneto-hydrodynamic simulation of a small part of the solar atmosphere. The ”engine” of the heating mechanism is the solar photospheric velocity field, that braids the magnetic field into a configuration where energy has to be dissipated. The initial magnetic field is taken from an observation of a typical magnetic active region scaled down to fit inside the computational domain. The driving velocity field is generated by an algorithm that reproduces the statistical and geometrical fingerprints of solar granulation. Using a standard model atmosphere as the thermal initial condition, the simulation goes through a short startup phase, where the initial thermal stratification is quickly forgotten, after which the simulation stabilizes in statistical equilibrium. In this state, the magnetic field is able to dissipate the same amount of energy as is estimated to be lost through radiation, which is the main energy loss mechanism in the solar corona.

The simulation produces heating that is intermittent on the smallest resolved scales and hot loops similar to those observed through narrow band filters in the ultra violet. Other observed characteristics of the heating are reproduced, as well as a coronal temperature of roughly one million K. Because of the ab initio approach, the amount of heating produced in these simulations represents a lower limit to coronal heating and the conclusion is that such heating of the corona is unavoidable.

Place, publisher, year, edition, pages
Stockholm: Institutionen för astronomi, 2004. 44 p.
Solen, Corona, Magneto hydro dynamik
National Category
Astronomy, Astrophysics and Cosmology
urn:nbn:se:su:diva-32 (URN)91-7265-798-7 (ISBN)
Public defence
2004-03-05, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00
Available from: 2004-02-04 Created: 2004-02-04Bibliographically approved

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