Authors: S. Hefti, H. Gruenwaldt, P. Bochsler, and M.R. Aellig
Reference: J. Geophys. Res., 105, 10,527-10,536, 2000.
We use the charge time-of-flight (CTOF) mass and charge spectrometer ot 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 T76 from the O7+ and O6+ abundance ratios in the period from days 92 to 299 of the 1996 (Carrington Rotations 1908 to 1912). The freeze-in temperature is a conserved property of the solar wind because the charge states do not charge 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 X 106 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.