Mathematics – Logic
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt..........s&link_type=abstract
PhD Dissertation, Finnish Meteorological Inst. Helsinki, Finland
Mathematics
Logic
Lyman Alpha Radiation, Solar Wind, Interstellar Gas, Interplanetary Medium, Hydrogen Atoms, Ionization, Ulysses Mission, Monte Carlo Method
Scientific paper
This thesis studies Lyman alpha measurements as a tool to study solar wind properties. Interstellar hydrogen gas flows into the solar system and interacts with the Sun. Trajectories of hydrogen atoms are determined by the radiation pressure and the gravity of the Sun. Near the Sun the atoms get ionized mostly by the charge-exchange collisions with solar wind protons and by solar EUV photons. The hydrogen atoms scatter resonantly solar Lyman alpha photons and can be observed by measuring scattered Lyman alpha radiation. The work includes an introductory part and four original papers. In the introductory part relevant observations, a standard modelling of the problem, and a review of Lyman alpha observations near the Sun are presented. In the papers different methods to study the solar wind properties by measuring the interplanetary Lyman alpha intensity are presented. In Paper 1 it is shown that the best fit to the Lyman alpha data is obtained by assuming that there is a band of high ionization near the solar equator and broad plateaus from the band to the poles. In Paper 4 the method to model the ionization rate developed in Paper 1 is used to study the differences in Lyman alpha observations when the ionization rate is deduced from Ulysses observations or using a so-called harmonic model where the ionization rate is a sinusoidal function of the solar latitude. In Paper 2 the effect of the temporally varying solar wind and the solar radiation are studied. In Paper 3 a Monte Carlo method is used to study combined temporal and latitudinal effects observable in Lyman alpha intensities. The results show that the stationary models can be used to calculate the interplanetary Lyman alpha intensities reasonably well, when lines-of-sight are directed toward the sidewind direction. However, the downwind direction intensities are strongly modified by temporal effects.
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