High-latitude thermospheric vertical wind activity from Dynamics Explorer 2 Wind and Temperature Spectrometer observations: Indications of a source region for polar cap gravity waves

Abstract

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 s, 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, maximizing 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 correlation was found between solar illumination and σ(Vz) at high latitudes, although the dayside vertical wind activity may be slightly reduced compared to night and twilight intervals. However, a clear relationship to geomagnetic activity, as measured by the AE index, was found; vertical wind activity increases with increasing AE. We interpret these results as a possible signature of polar cap gravity waves with sources in or near the midnight-dawn auroral oval. We use the probability density functions of σ(V z), separated by AE, to infer the temporal characteristics of the wave source and consequently to provide preliminary estimates of the production rates of polar cap gravity waves. Copyright 2002 by the American Geophysical Union.