Change search
ReferencesLink to record
Permanent link

Direct link
An Ab Initio Approach to the Solar Coronal Heating Problem
Stockholm University, Faculty of Science, Department of Astronomy.
2005 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 618, no 2, 1020-1030 p.Article in journal (Refereed) Published
Abstract [en]

We present an ab initio approach to the solar coronal heating problem by modeling a small part of the solar corona in a computational box using a three-dimensional MHD code including realistic physics. The observed solar granular velocity pattern and its amplitude and vorticity power spectra, as reproduced by a weighted Voronoi tessellation method, are used as a boundary condition that generates a Poynting flux in the presence of a magnetic field. The initial magnetic field is a potential extrapolation of a SOHO/MDI high-resolution magnetogram, and a standard stratified atmosphere is used as a thermal initial condition. Except for the chromospheric temperature structure, which is kept nearly fixed, the initial conditions are quickly forgotten because the included Spitzer conductivity and radiative cooling function have typical timescales much shorter than the time span of the simulation. After a short initial start-up period, the magnetic field is able to dissipate (3-4) × 106 ergs cm-2 s-1 in a highly intermittent corona, maintaining an average temperature of ~106 K, at coronal density values for which simulated images of the TRACE 171 and 195 Å passbands reproduce observed photon count rates.

Place, publisher, year, edition, pages
The American Astronomical Society , 2005. Vol. 618, no 2, 1020-1030 p.
Keyword [en]
MHD; Sun: corona; Sun: magnetic fields
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-23512DOI: 10.1086/426063OAI: diva2:192436
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

Open Access in DiVA

No full text

Other links

Publisher's full text
By organisation
Department of Astronomy
In the same journal
Astrophysical Journal
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 18 hits
ReferencesLink to record
Permanent link

Direct link