Disputation: Andres Spicher
Master i fysikk Andres Spicher at the Department of Physics will be defending the thesis Multiscale characterization of plasma irregularities in the polar ionosphere using in situ measurements for the degree of Ph.D.
Trial lecture - time and place
- Professor James William LaBelle, Dartmouth College, USA
- Professor Claudia Stolle, University of Potsdam, Germany
- Professor Joakim Bergli, University of Oslo, Norway
Chair of defence
Associate Professor Helge Balk , University of Oslo, Norway
- Associate Professor Wojciech Miloch, University of Oslo, Norway
- Professor Jøran I. Moen, University of Oslo, Norway
- Associate Professor Lasse Claussen, University of Oslo, Norway
Turbulence and irregularities are very common in the ionosphere, the ionized layer of the Earth’s upper atmosphere. Such irregularities can, among others, degrade high frequency radio communication and disturb Global Navigation Satellite Systems (GNSS) signals. With the increase of human activity relying on such systems in the polar regions, a detailed understanding of the mechanisms responsible for their creation is of increasing importance.
Motivated by the classical view that large clouds of enhanced plasma density called “polar cap patches” are dominant sources of irregularities in the high latitude ionosphere, we used data from the Swarm satellites (from European Space Agency ESA) to investigate when and where polar cap patches occur. We showed that patches prefer winter conditions in both hemispheres, and occur more often in the southern hemisphere. This strengthens previous studies about the northern hemisphere, and shed more light on the southern hemisphere. In addition, also using Swarm data, we estimated how fast the instability mechanism called the gradient drift instability (GDI) could generate irregularities in patches. The short times found support the existing view that the GDI may play an important role in the structuring of polar cap patches.
Furthermore, to characterize in more detail irregularities at scales ranging from several kilometers to a few meters, we zoomed in using high-resolution measurements from the Investigation of Cusp Irregularities (ICI) sounding rockets (UiO experiment). The observations based on the rocket data gave further evidence of the importance small-scale processes, of the GDI, and of particle precipitation at high latitudes. In particular, we provided new insight on the nature of irregularities associated with the two latter mechanisms. The results suggest that the GDI creates coherent structures characterized by intermittency, i.e., large but sparse events, while direct particle precipitation creates more turbulent-like structures.