Disputation:
The coronal heating problem





Boris V. Gudiksen
Institutet för solfysik
vid
Kungliga vetenskapsakademien
Stockholms Observatorium
Albanova
Roslagstullsbacken 21
5 Mars  2004, kl. 13.00
Sal B52


Avhandlingen diskuterar hur upphettningen av solkoronan sker. Flertal teoretiska modeller existerar men man har inte kunnat avgöra vilken som är den mest relevanta. Boris Gudiksen visar med sitt arbete att med vår nuvarande kunskap om solen så är en av modellerna tillräcklig för att förklara upphettningen av koronan: konvektionen i fotosfären ger energi till magnetfält som sedan avger sin  energi till koronan.

Sammanfattning på engelska:
The heating of the solar corona has been investigated for several decades and a large number of models theoretically able to produce the right amount of heating has been constructed. It has not been possible to produce quantitative evidence that would establish any of them as the most important heating mechanism at work in the solar corona. This thesis is an attempt to produce the crucial quantitative estimate of the heating. 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 a mechanism reproducing the statistical and geometrical fingerprint of the solar granulation. Using a standard model atmosphere as the thermal initial condition, the model goes through a short start up phase where the initial thermal stratification is quickly forgotten and then enters statistical equilibrium. The magnetic field is able to dissipate the same amount of energy as is estimated to be lost from the solar corona through radiation, believed to be the main energy loss mechanism for the plasma in the solar corona. The 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 is a minimum and unavoidable.

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