Vertical Neutral Wind Measurements in the Midlatitude Thermosphere

Direct Doppler shift measurements of the OI red line and green line airglow emissions are used to investigate the magnitude of vertical winds at the Arecibo and Millstone Hill optical facilities. Thousands of data samples between 2014-2017 have been collected using sensitive imaging Fabry-Perot interferometers with precise frequency calibration and instrument drift monitoring at each site. In 2016, quiet time vertical winds at Arecibo sampled over 31 days centered on the equinoxes and solstices, vary from the semidiurnal mean by +/- 30 m/s. That 1-sigma variability is approximately 1/2 that of the horizontal zonal wind component, and 2/3 that of the meridional wind component. Quiet time vertical winds at Millstone Hill vary from their semidiurnal mean by +/- 23 m/s, a 1-sigma variability that is approximately 1/3 that of the zonal wind component, and 40% of the meridional wind component. Storm time vertical winds commonly exceed 100 m/s at each site, and a correlation between vertical wind velocity enhancements and the midnight temperature maximum is also evident at Arecibo. A single night of meridional neutral wind measurements derived from the metastable 1083nm He emission imply neutral wind velocities approximately four times stronger than meridional winds near the F-region peak. Transport in the upper thermosphere is seldom dictated by hydrostatic equilibrium.