In this paper we make several observations on the Gram- Charlier and Edgeworth series, which are methods for modeling and approximating probability density functions.We present a simplified derivation which highlights both the similarity and the differences of the series expansions, that are often obscured by alternative derivations. We also introduce a reformulation of the Edgeworth series ...

This thesis presents three-dimensional modelling of artificial aurora in the ionospheric F layer, induced by high frequency (HF) O-mode radio waves from the EISCAT heating facility. Understanding how HF radio waves produces enhanced emission in the ionosphere has been one of the one of the major motivations for conducting heating experiments during the last decades. A key element for understanding ...

The influence of Arctic summer sea ice area on autumn and winter climate in the extra-tropic Northern hemisphere is investigated. During the last decades, the Arctic has warmed more than twice the global average rate, a phenomenon called the Arctic Amplification (AA). AA involves a remarkable decrease of the Arctic sea ice cover and a decrease of the latitudinal temperature gradient. Both are supposed ...

The studies about the climatic changes have always more underlined the importance of the climatic balance of the Arctic regions. For this reason the need of monitoring the Arctic becomes always more urgent. To measure the sea ice thickness, the sea ice cover, the motion of the glaciers and to discriminate the various kind of ice are only several of the challenges about the Arctic monitoring. But the ...

The dependence of fluctuations on electron-neutral collision frequency (V_en) and the radial location is investigated in an electron cyclotron resonance plasma in a divergent magnetic field region for a set of magnetic fields. Results indicate that the fluctuations depend strongly on the collision frequency. At lower magnetic fields and V_en, the fluctuation levels are small and ...

The work described in this thesis was carried out to investigate how additional permanent magnets (PM) could affect the confinement and ion beam generation in a plasma which expands from a helicon source. PMs added to a plasma source systems has been shown to provide an increased plasma confinement, but is not widely used. This inexpensive and cheap method of using PMs which does not require any ...

Naturally Enhanced Ion-Acoustic Lines (Neials) are small-scaled and short-lived phenomena in the ionosphere, which is widely researched internationally. At present, the search for Neials is a tedious task that has to be done through visual inspection. This is often a time-consuming process and limits the research on Neials. By automating the means of locating the Neials, the access to them will be ...

The aim of this study was to investigate the altitudinal and diurnal variations of light ion densities in the topside ionosphere during the 23rd and 24th solar maximums. This made it possible to understand the behavior of the ion composition after extended solar minimum and compare how it differs from the preceding solar maximum. The observed variations are compared with estimates of empirical (IRI) ...

Modern science is based on observation, and its advances are limited by what is possible to observe. For centuries optical microscopy was limited by the diffraction of light, making structures closer together than half the wavelength of light unresolvable. In recent years, the new field of optical nanoscopy has emerged, enabling diffraction-limited structures to be resolved. As opposed to ...

A stochastic model for intermittent fluctuations due to a super-position of uncorrelated Lorentzian pulses is presented. For a constant pulse duration, this is shown to result in an exponential power spectral density for the stationary process. A random distribution of pulse durations modifies the frequency spectrum, and several examples are shown to result in power law spectra. The distribution of ...