Direct evidence of transport processes in the thermospheric diurnal tide

Measurements of neutral composition and temperature obtained between December 6, 1975, and September 17, 1976, with instruments aboard the near-equatorial AE-E satellite are analyzed to determine the diurnal variations at altitudes from 145 to 295 km. The general trends, including the shift in oxygen phase from afternoon at high altitudes to morning at low altitudes, are reproduced by circulation theories. The oxygen and helium variations show small departures from diffusive equilibrium below 200 km that are consistent with wind-induced diffusion and provide the first direct evidence of transport processes in the diurnal tide of the thermosphere.