THERMOSPHERIC MOLECULAR-OXYGEN MEASUREMENTS USING THE ULTRAVIOLET SPECTROMETER ON THE SOLAR MAXIMUM MISSION SPACECRAFT

The technique of solar occultation has been utilized to measure molecular oxygen densities in the 140- to 220- km altitude region. The ultraviolet spectrometer/polarimeter on the Solar Maximum Mission (SMM) spacecraft was operated in the occultation mode between 1985 and the end of 1989, at wavelengths of 137.46 and 139.06 nm. This covered the period from the solar sunspot minimum in 1986 to December 1989 when solar activity was near the sunspot maximum. The observed solar area was 10x10 arc s2, which yields O2 concentrations with an altitude resolution of 0.17 km. These molecular oxygen data are compared with O2 data obtained under similar conditions of local time, location, and solar activity using other techniques. SMM data are also compared with the mass spectrometer/incoherent scatter (MSIS) - 86 model. Good agreement is found near 150 km for several O2 temporal variations including the annual cycle, local time, solar activity, and magnetic activity. Unlike the model, the measured density profiles exhibit no significant increase with increasing solar activity. The disagreement of the SMM O2 data with the MSIS-86 model increases with increasing altitude.