Gravity waves observed by ionospheric temperature measurements in theFregion

Ion temperature measurements below the F peak have revealed the presence of a fine structure in the ionospheric temperature. The measurements were made with an Ion Energy Analyzer carried aboard a low-altitude polar-orbiting satellite. The temporal resolution of the Ion Energy Analyzer was 3 seconds corresponding to a horizontal spatial resolution of approximately 23 km. At the altitudes of these measurements the ions and neutral species of the atmosphere have a common temperature; thus the temperature structure present in the ion temperature must also be present in the neutral atmosphere as well. The temperature structure is observed to have a wave-like character with wavelength of the order of 200 km. The fractional temperature variation is typically 13%. Much of the observed wave structure is interpreted as internal atmospheric gravity waves, and the results obtained here are compared with the existing theory. A large portion of the wave structure observed cannot be explained on the basis of the simple linearized gravity wave theory. This wave structure is either the result of some as yet unspecified phenomenon or is the result of gravity waves in a real atmosphere where the idealized conditions and restriction from linearization are removed.