A mass spectrometric investigation of the lower thermosphere above Fort Churchill with special emphasis on the helium content

A quadrupole mass filter, designed for rocket-borne measurements of the thermosphere helium content, is described. This instrument was flown from Fort Churchill, Canada, on December 12, 1966, 1305 LT, and gave data in the altitude range of 110–155 km. The measured helium number densities were found to be higher by a factor of 5 than predicted by CIRA 1965. In addition, the density profiles of nitrogen (N2) and molecular oxygen (O2) were also obtained. Some conclusions concerning the turbopause level and the winter helium bulge are drawn.