Medium Scale Gravity Waves in the Thermosphere Observed by the AE-C Satellite

Atmospheric Explorer C (AE-C) satellite data were used to investigate the spectral characteristics of medium-scale wavelike structures (horizontal-scale size from tens to hundreds of kilometers) observed in the neutral and ionized components of the thermosphere at about 250-km altitude. Data for the neutral densities of oxygen, nitrogen, and helium from the Neutral Atmosphere Temperature Experiment, the electron density and temperature from the Cylindrical Electrostatic Probe were analyzed for a part of an orbit in the northern hemisphere between 54° and 10° geographic latitudes. Coherent wave systems are shown by employing direct comparison of the fluctuations of the parameters, comnputations of their cross-correlation functions and spectral analysis. Waves from many tens to hundreds of kilometers are found in the fluctuations of all parameters. A power law decrease of the spectrum is also found with different rates for the various densities and electron temperature, -3.2 for oxygen, -4.6 for nitrogen, 0.23 for helium, -1.96 for the electron density, and -1.66 for the electron temperature. These results complement similar studies of large-scale structures reported in another paper [8]. They are typical of those obtained for other parts of this orbit and for other orbits. Unlike largescale waves, medium-scale waves appear to attenuate after about 4-5 cycles, consistent with lower altitude sources and known loss mechanisms. An exception is shown with wave structure throughout the entire time record, however, implying a source in the F region.