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”Auroral Structure and Kinetics” (ASK) is a multispectral auroral imager,developed and built by University of Southampton, UK, and Royal Institute ofTechnology, Sweden. The scientific objective of the instrument include characterisationof both high and low energy electron precipitation in aurora with highspatial and temporal resolution, and direct observation of plasma drifts in theionosphere. ASK consists of three cameras taking images in different spectrallines. One part of this thesis deals with the development of the data acquisitionsystem for the instrument. This included the hardware part (computers controllingthe cameras)and the software for operation of ASK. ASK was installedon Svalbard in November 2005, and examples of first data are presented. Thesecond part of the thesis treats the problem of estimation of motions from theauroral sequences. Robust optical flow estimation algorithm has been applied toauroral sequences, and new formulations specific to the imaging of metastableions (carried out by ASK) are suggested.

Data from an ionospheric heating experiment in Tromsø have beenanalyzed. The experiment was carried out during auroral conditions inOctober 2006. Beside data from the EISCAT UHF radar also opticaldata were recorded with the ASK (auroral structure and kinetics) instrumentand enhancements of backscattered power from the E-regionwere studied. Two simultaneous layers of instability with an altitudeseparation of 5 km are observed at an altitude of 120 km. Thetwo layers differ in their spectral characteristics and show different timeevolution. For one heating cycle it was also found that auroral processescorrelate to the strength of enhancements and the characteristics of theion line spectra.

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Fluctuations in the solar wind characteristics such as speed, temperature, magnetic strength and density are associated with pulsations in the magnetosphere. Coherent magnetohydrodynamic waves in the solar wind may sometimes be a direct source of periodic pulsations in the frequency interval 1 to 7 mHz in the magnetosphere. In studies of the solar wind and the way its variation affects the magnetosphere, the significance of different frequency components and their signal fonn are of interest. Spectral analysis and signal reconstruction are important tools in these studies and in this report the MultiTaper Method (MTM) of spectral analysis is compared to the "classic" method, using the Hanning window and Fourier transformation. The MTM-SSA toolkit, developed by Department of Atmospheric Science at the University of California, is used to ascertain whether the MTM might be suitable. The advantages of the MTM are reduced information loss in analysed data sequences and statistical support in the analysis. Besides the compared methods of spectral analysis, an attempt has been made to test the validity of the adiabatic law, assumed as the relation between the thermal pressure and the density in the solar wind plasma. It was unfortunately difficult to estimate the gamma parameter of this relation, possibly due to the turbulent behaviour of the solar wind.

A study of ACE solar wind data at lAU, for the period from 1998 to early 2005, was conducted. This was done in order to find sudden solar wind pressure enhancements accounting for plasma transfer through the magnetopause. In order to get information about the extent and orientation of the structures found, a correlation of found events to data from the Wind satellite was done. The enhancements considered are those with a relative increase exceeding unity. These are found by applying a 1-hour box-car average to the data set. A part of the event distribution was found to vary at periodicities of 11 years, 140 days, and 29 days. Most of the pressure enhancements found were due to a corresponding increase in plasma density. The transverse extent of most of the structures found was rather large, i.e., of the order of 100 Earth radii and the mean orientation of the plasma fronts  were found  to lie between the radial direction and that of  the Archimedean spiral. The duration of most of the structures was shorter than 1 hour. An investigation of the direction of the GSE Z-component of the magnetic field of the events, showed that there was no predominant orientation.