Mathematics – Probability
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa12a0674i&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SA12A-0674
Mathematics
Probability
0358 Thermosphere: Energy Deposition, 2475 Polar Cap Ionosphere, 3369 Thermospheric Dynamics (0358), 3384 Waves And Tides
Scientific paper
The large-scale distribution of thermospheric vertical wind activity, from ~250 to 650~km altitude, was studied using observations from the Wind and Temperature Spectrometer on the Dynamics Explorer-2 satellite. We calculated the vertical velocity standard deviation, σ (Vz), within a sliding window of width 120~seconds, corresponding to an along-track distance of ~900~km. Maps of σ (Vz) in local magnetic time and invariant latitude reveal a high-latitude region of enhanced activity that largely fills the polar cap, maximising in the midnight--dawn sector. Separating the data by altitude suggests that most of the vertical wind energy present at 250--450~km is dissipated within a few hundred vertical kilometers. Northern and Southern hemisphere high-latitude σ (Vz) fields were found to be very similar, indicating no significant hemispheric differences. No strong dependence was found between solar illumination and the high-latitude σ (Vz), although the day-side vertical wind activity may be slightly reduced when compared to night and twilight intervals. However, a clear dependence on geomagnetic activity, as measured by the AE index, is present in the data, as the vertical wind activity increases with increasing AE. We interpret our results as evidence of polar cap gravity waves with sources in or near the midnight--dawn auroral oval. We use the probability density functions of σ (Vz), separated by AE, to infer the temporal characteristics of the wave source, and consequently to provide preliminary estimates of the rates of occurrence of polar cap gravity waves.
Conde M. G.
Innis John L.
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