Presentasjon av masteroppgave: Bjarne Grav

Coronal Heating by Magnetic Reconnection, Calculations of Quasi-Separatrix Layers


Several decades ago it was discovered that the outer layers of the Sun are much hotter than the photosphere. The mechanism or mechanisms heating the outer solar layers are not known, so this is known as the coronal heating problem. Two different categories of theories have emerged: wave theories and magnetic reconnection theories. Both wave features and magnetic reconnection have been observed in the Sun, so both theory categories are still possible theory candidates.

This thesis investigates a theory trying to predict where magnetic reconnection takes place, and thus if it can predict where heating takes place.

A program that calculates the degree of squashing Q has been developed and tested. The program has been applied to a 3D magnetic field produced by the stellar simulation code Bifrost. Bifrost produces realistic solar simulations and is therefore a good tool in the study of the Sun. Simulations have a big advantage over observations in testing this theory, since they can provide magnetic field data in 3D. Current observations don't provide data for the full 3D magnetic field, and rely on extrapolations of the magnetic field from the photosphere.

The calculated quasi-separatrix layers (QSLs) locate the magnetic null points in the field as expected, in addition to a lot of new potentially interesting areas where the magnetic field varies sharply. The full volume calculations of Q have been done by a method that relies on interpolation between layers, and some selected layers have been found by complete calculations for each point.

The QSLs have been compared to the corresponding simulated heating data from Bifrost. Results indicate that the calculated QSLs to a good degree correspond to where heating takes place, but that some heating also happens outside the calculated QSLs. Most of these discrepancies can probably be explained by numerical errors, so the conclusion is that this theory works well for predicting where heating will happen.

Veileder: Førsteamanuensis Boris Vilhelm Gudiksen, Institutt for teoretisk astrofysikk, UiO

Medveileder: Professor Viggo Hansteen, Institutt for teroretisk astrofysikk, UiO

Intern sensor: Professor David F. Mota, Institutt for teoretisk astrofysikk, UiO

Ekstern sensor: Øivind Wikstøl, Forsvaret

Publisert 6. juni 2016 14:04 - Sist endret 13. juni 2016 13:05