Heating of the high-latitude thermosphere during magnetically quiet periods

A persistent mid- to high-latitude heating phenomenon is observed in both hemispheres in data from the Ogo 6 quadrupole mass spectrometer. The phenomenon is evidenced by an increase in N2 density (indicative of a thermospheric temperature rise) and a depletion in helium (indicating an upwelling of air). The composition changes maximize near 0900 and 2100 UT, appear to corotate with the local magnetic pole, and are larger near equinox than near the summer solstice. The variation in latitude of the peak in the winter helium density (as a function of UT) is a specific manifestation of this general heating phenomenon.