Physics – Space Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1418i&link_type=abstract
Journal of Geophysical Research (Space Physics), Volume 107, Issue A12, pp. SIA 1-1, CiteID 1418, DOI 10.1029/2002JA009370
Physics
Space Physics
2
Meteorology And Atmospheric Dynamics: Thermospheric Dynamics (0358), Meteorology And Atmospheric Dynamics: Waves And Tides, Ionosphere: Polar Cap Ionosphere, Ionosphere: Ionospheric Disturbances
Scientific paper
Data obtained by the Neutral Atmosphere Composition Spectrometer (NACS) and the Wind and Temperature Spectrometer (WATS) instruments on Dynamics Explorer 2 (DE 2) show examples of large wave-like events in composition, vertical wind, and temperature, particularly (perhaps almost exclusively) at high geomagnetic latitudes. These events are believed to arise due to atmospheric gravity waves (AGWs). If so, the various perturbation quantities of mass density, pressure, temperature, horizontal wind, and vertical wind should be related in a manner consistent with the AGW theory. An analysis of a subset of the WATS (vertical and horizontal wind and temperature) and NACS data (number density and, hence, mass density) and pressure (as a derived quantity, from number density and temperature) was performed to investigate whether such perturbations could be clearly shown to be due to AGWs by comparing quantitatively the various simultaneous data sets with AGW theory. Seven examples of wave-like events in the vertical wind were studied, together with the accompanying variations in mass density, pressure, temperature, and horizontal wind. The pressure (acoustic) component of the density variation was calculated and then 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 altitude displacements. Phase lags in the number density perturbations between different species also appeared consistent with the AGW theory. Horizontal velocity perturbations in phase with the pressure perturbations were also seen. It is concluded that the oscillations are consistent with acoustic-gravity waves, where the pressure perturbation is nonnegligible. Phase relationships between the various observables can define the direction of wave travel to within 90° of azimuth, relative to the direction of spacecraft motion. For the seven cases detailed here, 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 Maria M.
Innis John L.
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