Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsa41a..16i&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SA41A-16
Physics
2475 Polar Cap Ionosphere, 3369 Thermospheric Dynamics (0358), 3384 Waves And Tides, 2435 Ionospheric Disturbances
Scientific paper
A detailed analysis has been undertaken of certain wave-like events, seen in the upper polar thermosphere by Dynamics Explorer 2. While such oscillations have been ascribed to gravity waves, a detailed multi-parameter comparison with gravity wave theory has yet to be performed. We use data from the Wind and Temperature Spectromter (WATS), and the Neutral Atmosphere Composition Spectrometer (NACS), to compare the perturbation quantities of mass density, pressure, temperature, horizontal wind and vertical wind with gravity wave theory for several of these events. The pressure (acoustic) component of the density variation was calculated, and subtracted from the total density variation, allowing the wave-induced vertical displacement amplitude to be found. This was compared to the vertical wind amplitude, via a spectral analysis, to yield estimates of the possible AGW frequency. The observed variation in the ratio of O:N2 number densities, during the course of the oscillations, was found to be consistent with the calculated altitudinal displacements. Horizontal velocity perturbations in phase with the pressure perturbations were also seen. It is concluded that the oscillations are consistent with acousto-gravity waves, where the pressure perturbation is non-negligible. Phase relationships between the various observables can define the direction of wave travel to within 90 degrees of azimuth, relative to the direction of spacecraft motion. The derived (intrinsic) wave frequencies are close to, but slightly less than, the estimated local Brunt-Vaisala frequency, while the vertical displacement amplitudes were typically around 25 km. All of the wave events studied in this work were located at high-latitudes, poleward of the nominal location of the auroral oval.
Conde M. G.
Innis John L.
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