Master of Science Mahith Madhanakumar will Thursday February 5th, 2026, at 12:15 hold his Thesis Defense for the PhD degree in Science. The title of the thesis is:
«Ionospheric Plasma Structuring Across a Range of Scale Sizes and GNSS Scintillation During Different Geomagnetic Conditions »
The purpose of this thesis is to expand the current knowledge on the ionospheric conditions during periods of GNSS scintillation and the associated structuring of plasma across different scale sizes in the high latitude ionosphere. Specifically, we developed a methodology in order to identify the presence of ionospheric irregularities within an ambient plasma. By applying the methodology to the dayside ionosphere, we observed GNSS phase scintillation to be predominantly associated with irregularities in the F-region. The associated plasma conditions revealed the presence of elevated electron and ion temperatures in the F-region. The observations therefore support the importance of cusp/auroral dynamics in producing irregularities that can perturb GNSS signals in the dayside ionosphere.
We also conducted a multi-instrument study at the dayside polar ionosphere to understand the evolution of scintillation strengths during periods of quiet geomagnetic conditions. Intense amplitude and phase scintillation were observed simultaneously on multiple GNSS signals that persisted for more than one hour in duration. The associated ionospheric conditions revealed dense polar cap patches, co-located with regions of soft electron precipitation and ion Joule heating, to be an important source of plasma irregularities. Furthermore, it was observed that a reversal in the interplanetary magnetic field components, By and Bz , led to the formation of a region of depleted density in the polar ionosphere. This resulted in the significant weakening of irregularities at Fresnel and kilometer scales (and hence a reduction of amplitude and phase scintillation) in the post-noon sector.
Furthermore, we also examined the progress and decay of irregularities and plasma structures with scale sizes from three meters to several hundreds of kilometers during the May 2024 superstorm. Simultaneous existence of irregularity scales from three meters to several kilometers were observed at the dayside auroral ionosphere during the storm’s expansion phase on 10 May. Intense irregularities existed for about four hours and were associated with dense plasma structures from sub-auroral latitudes and energetic particle precipitation. As the storm progressed, Fresnel irregularities and structures with scales of the order of several hundreds of kilometers remained at substantially weakened levels. On the other hand, intense three meter irregularities in the E-region and kilometer scale structures associated with GNSS phase fluctuations persisted for about 24 hours. In contrast to 10 May, the dayside auroral ionosphere on 11 May was depleted of irregularities across all scale sizes due to the lack of dense ionospheric plasma and energetic particle precipitation.
1st Opponent: Senior Researcher Dr. Alan Wood, UK MET Office,
2nd Opponent: Professor Hilde Nesse, University of Bergen,
Internal member and leader of the committee: Professor Odd Erik Garcia, IFT, NT-fak, UiT