The polar solar wind from 2.5 to 40 solar radii: Results of intensity scintillation measurements.

摘要

The supersonic expansion of the solar corona into interplanetary space, the solar wind, was predicted in 1958 and conclusively detected by satellite measurements in 1962. However, due to the difficulty of obtaining data close to the sun and the complexities of plasma physics, the problem of solar wind acceleration remains an enigma. Radio propagation measurements, which have been carried out for nearly the last 3 decades, are one of the few means of measuring the plasma properties in the acceleration region of the solar wind.; In this thesis we present results from intensity scintillation observations (IPS), which probe the polar solar wind at solar minimum. Our closest observation, at 2.4 solar radii, is the closest ever reported. We have found that: (1) the mean velocity is already very high, even at 2.4 solar radii, perhaps even higher than further out; (2) a wide distribution of radial velocities is present in our observations (e.g. 300 km/s {dollar}<{dollar} Vradial {dollar}<{dollar} 1200km/s at 11 solar radii)--the width of this distribution decreases with increasing distance from the sun; (3) the observed Alfven wave amplitudes are consistent with WKB evolution; (4) our observations confirm the high degree of anisotropy measured with other radio propagation techniques; (5) there is non radial flow inside of 12 solar radii consistent with the predicted super radial expansion of the polar solar wind. The velocities determined by IPS are the apparent velocity of density irregularities with scales of the order of 10 to 100 km. If the density irregularities are non-propagating then IPS measures the flow velocity, otherwise IPS measures the flow speed plus the group velocity of the density waves.; A new model for extracting information from intensity scintillations is presented. The model incorporates: our knowledge of the spectrum of electron density fluctuations gained from other radio propagation observations; the effects of Alfven waves; the super radial expansion of the corona near the sun; the spiral orientation of the field far from the sun; the bimodal nature of the solar wind; and the line-of-sight integration.