Disputas: Charalambos Kanella

M. Sc. Charalambos Kanella ved Institutt for teoretisk astrofysikk vil forsvare sin avhandling for graden ph.d.:On the Identification of Small-Scaled Heating Events in MHD Simulations of the Solar Corona.

Charalambos Kanella
Charalambos Kanella
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Bedømmelseskomité

  • Oskar Steiner, PhD, Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany (opponent)
  • Tom van Doorsselaere, PhD, KU Leuven, Belgium (opponent)
  • Professor, PhD, David F. Mota, Institute of Theoretical Astrophysics, University of Oslo (administrator)

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Populærvitenskapelig sammendrag av avhandlingen

Identifiseringen av tredimensjonale småskala oppvarmingshendelser i numeriske simuleringer har ført oss et skritt nærmere å løse et av de største mysteriene i astrofysikken.

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The identification of small-scale 3-D heating events in numerical simulations brought us a step closer to solve one of the biggest mysteries in astrophysics. 

The identification of small scale 3-D heating events in the solar atmosphere is an extremely difficult task. Until we succeeded. This brought us a decisive step closer to solve a 70-year-old mystery in astrophysics: “Why the solar corona, the outer layer of the Sun’s atmosphere, is much hotter than the solar surface?”

To succeed, we used a powerful code to simulate the solar atmosphere, and an innovative identification method used in medical imaging for multi-dimensional image analysis.

We discovered that the largest population of heating events is energetically small events, with small-spatial extent that leave shortly. This finding is very important because it favored an old but famous theory: “Small scale events, but still unobserved due to the limitations of our telescopes, is the main heating mechanism of the solar corona.”

Being able to identify 3D heating events allows us to study their geometrical characteristics in all spatial dimensions. For instance, we studied how rounded or how big they could be. This is important because in real observations we are doomed to capture 2-D images, and the process of combining 2-D images to create 3-D ones is always biased.

Each event occupies a volume and has a duration. Knowing this information, we compared those parameters with the energy released from each event. This way, we found rough approximations between the parameters that could help observers deduce information by observing one parameter than another.

Having identified heating events in numerical simulations allows to use parameters calculated in the simulation, such as temperature and electron density, and therefore synthesize images such those in real observations. But the most interesting aspect is the fact that we synthesized images of regions exhibiting only heating events. This way, we helped observers to understand the reasons they cannot identify small-scale events in real observations and show them how heating events would possibly look like.

Even though the results are not conclusive, they point towards the correct direction: Further research and more brilliant ideas and methods are needed to solve the mystery.

Publisert 26. sep. 2018 20:54 - Sist endret 18. aug. 2021 14:21