Paper presented at the 31st ESLAB Symposium, 22-25 September 1997, ESTEC, Noordwijk, The Netherlands.
The SOHO/CELIAS/CTOF (Charge Time Of Flight) mass spectrometer measures the ionic and elemental composition of minor ions in the solar wind with unprecedented time resolution. This allows the study of small scale changes in coronal electron temperature and density that manifest themselves in a variation of freeze-in temperatures. Variations are observed on timescales down to several hours, sometimes without any substantial change in solar wind plasma parameters.
In the latter case we have a subtle tool to distinguish solar wind source regions, that are not accessible to a plasma parameter survey (velocity, kinetic temperature, proton density, etc.).
The application of a simple model of the coronal expansion to calculate the resulting freeze-in temperatures shows, how changes in coronal conditions can be quantified. We consider the electron temperature and density at the base of the corona, the velocity and the corresponding power law indices to influence the measured freeze-in temperatures.
The absolute Fe density in the solar wind is also analysed and compared to previous values. In addition elemental abundance such as the Fe/H ratio are analysed as a function of the velocity in order to assess a possible velocity dependence as it is expected from some models of chromospheric fractionation.