Direct in situ measurements of wave propagation in the neutral thermosphere


  • George P. Newton,

  • David T. Pelz,

  • Hans Volland


The density gages on the Explorer 32 satellite have measured local variations in the atmospheric density that confirm that waves propagate in the neutral atmosphere. The waves were observed in the northern hemisphere over the altitude range from 286 km (satellite perigee) to at least 510 km. The waves are most prevalent at the higher latitudes near the auroral zone (orbit inclination is 65°) and were observed most frequently in the late evening and early morning hours, but were not limited to these latitudes and times. The apparent vertical half-wavelengths of the waves increase with altitude from 1 km at 286-km altitude to 70 km at 510-km altitude. Apparently four integrally related wavelengths have been observed, a ‘fundamental’ and the second, third, and fourth harmonics. The wave density perturbation half-amplitudes range from the limit of detectability to the largest observed of 50% of the smoothed density profile value. These waves are interpreted as free internal gravity waves propagating predominately north-south, or south-north, with maximum horizontal wavelengths between 130 and 520 km. The altitude dependence of the apparent vertical half-wavelengths results from the satellite moving with varying vertical velocity through a slowly propagating wave pattern with nearly vertical phase planes. This interpretation is consistent with observations of large-scale traveling ionospheric disturbances by Thome and Georges.