Other
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996sao..rept.....e&link_type=abstract
Technical Report, Smithsonian Astrophysical Observatory Cambridge,MA United States
Other
Solar Wind, Line Spectra, Electron Energy, Mathematical Models, Plasma Composition, Solar Corona, Solar Spectra, Soho Mission, Solar Wind Velocity, Velocity Distribution
Scientific paper
Knowledge of the plasma conditions in the inner corona is essential for solar wind modeling since any attempt to explain the expansion of the solar wind plasma depends on information in the inner corona to select and constrain the solar wind expansion models. Of particular interest are the temperatures of the different particle species. The temperatures of protons and heavy ions such as oxygen can only be derived from measurements of spectral lines. As the width of spectral lines reflects both thermal and non-thermal random motions only an upper limit can be placed on the temperature of these particles. The electron temperature on the other hand can be derived from measurements of spectral line intensities by comparing the measured line ratios to the ratios calculated from theoretical models, and from in situ charge state measurements. The idea is that the charge state of the considered element is a function of the local electron temperature only, and that the charge state 'freezes in' at a certain heliocentric distance and remains constant beyond that distance. Therefore, the in situ charge state ratio reflects the electron temperature in the inner corona. In deriving these charge state temperatures it is assumed that all elements and charge states have the same flow speed and the same temperature. Also inherent in these temperature estimates is the assumption that the electron velocity distribution function is Maxwellian. The effect of non-Maxwellian velocity distribution functions and differential flow speeds have been discussed in Owocki and Scudder (1983) and Esser and Leer (1990), respectively. Since the message carried by the charge states is obscured by these different assumptions, model calculations are necessary to extract the desired information from the observations. The goal of the funded study is to develop the necessary solar wind models, and to compare the derived electron temperatures to those derived from spectral line intensity measurements carried out from the SOHO satellite.
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