Proceedings of the 31st ESLAB Symposium, ESA-SP (1998).
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. As shown by different authors the charge states of minor ions in the solar wind provide a powerful tool to detect changes of the electron temperature profile in the solar corona. We apply this well-known method to interpret the SOHO/CELIAS/CTOF data. Due to the high sensitivity of the CTOF sensor we can perform coronal diagnostics using solar wind in situ measurements with high time resolution. We briefly describe the relevant quantities and approximations to determine the freezing of charge states of minor ions. The application of a simple description of the coronal expansion to calculate the freeze-in temperatures results in a parametrization of the latter with coronal properties. The influence of the coronal parameters is discussed. We vary the temperature profile to match the observed freeze-in temperatures. Analysis of extended periods of time shows considerable variations of the temperature profile in the inner corona on short time scales. We discuss the sensitivity of the results to some of the assumptions, such as the electron density and the superradial expansion.