Oxygen freeze‐in temperatures measured with SOHO/CELIAS/CTOF

We use the charge time‐of‐flight (CTOF) mass and charge spectrometer of the charge, element, and isotope analysis system (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) to determine the solar wind oxygen freeze‐in temperature T 76 from the O 7+ and O 6+ abundance ratios in the period from days 92 to 229 of 1996 (Carrington Rotations 1908 to 1912). The freeze‐in temperature is a conserved property of the solar wind because the charge states do not change after a distance of a few solar radii. Therefore it is an ideal in situ diagnostic for remote sensing of the inner solar corona. We determine the mean freeze‐in temperature during the selected period to be 1.6 × 10 6 K. We use it to map coronal regions of different temperatures and to determine the separation between such regions based on our observation of abrupt transitions of the freeze‐in temperature. We find a upper limit for the separation in the inner corona of 1000 km.