Multi-taper method for spectral analysis and signal reconstruction of solar wind data

Sammanfattning: 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.