[1] 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, s(V z ), within a sliding window of width 120 s, corresponding to an along-track distance of $900 km. Maps of s(V z ) 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 s(V z ) fields were found to be very similar, indicating no significant hemispheric differences. No strong correlation was found between solar illumination and s(V z ) 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 s(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.

Abstract. An ensemble of space-borne and ground-based instruments has been used to evaluate the quality of the version 2.2 temperature retrievals from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The agreement of ACE-FTS temperatures with other sensors is typically better than 2 K in the stratosphere and upper troposphere and 5 K in the lower mesosphere. There is evidence of a systematic high bias (roughly 3-6 K) in the ACE-FTS temperatures in the mesosphere, and a possible systematic low bias (roughly 2 K) in ACE-FTS temperatures near 23 km. Some ACE-FTS temperature profiles exhibit unphysical oscillations, a problem fixed in preliminary comparisons with temperatures derived using the next version of the ACE-FTS retrieval software. Though these relatively large oscillations in temperature can be on the order of 10 K in the mesosphere, retrieved volume mixing ratio profiles typically vary by less than a percent or so. Statistical comparisons suggest these oscillations occur in about 10% of the retrieved profiles. Analysis from a set of coincident lidar measurements suggests that the random error in ACE-FTS version 2.2 temperatures has a lower limit of about ±2 K.

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Abstract.Large-scale distribution of thermospheric vertical wind activity was studied using observations from the Wind and Temperature Spectrometer on the Dynamics Explorer-2 satellite. We calculated the vertical velocity standard deviation, a(Vz), within a sliding window of width 120 seconds, corresponding to an along-track distance of --900 km. Maps of a(Vz) in local magnetic time and invariant latitude reveal a high-latitude region of enhanced activity that largely fills the polar cap. Activity appears to be a maximum in the midnight-dawn sector of the cap, possibly at the nominal auroral oval latitude. We provisionally interpret our results as evidence of polar cap gravity waves with sources in or near the midnight-dawn auroral oval. Waves propagating poleward effectively fill the cap with vertical wind oscillations. Equatorward propagating waves move approximately parallel to the local thermospheric wind, resulting in the possibility of critical-layer dissipation.