A comparison of quiet time thermospheric winds between FPI observations and model calculations

We investigate local time, seasonal, and longitudinal variations of thermospheric horizontal winds at midlatitudes during geomagnetically quiet times by comparing winds from observations, an empirical wind model, and a numerical model. The observations are from three Fabry-Perot interferometers (FPIs), the empirical model is the most recent version of the Horizontal Wind Model 14 (HWM14), and the numerical model is the Thermosphere-Ionosphere-Electrodynamics General Circulation Model of the National Center for Atmospheric Research. The three FPI stations are located at Xinglong (geographically 40.2 degrees N, 117.4 degrees E; geomagnetically 35 degrees N) and Kelan (geographically 38.7 degrees N, 111.6 degrees E; geomagnetically 34 degrees N) in China and at Millstone Hill (geographically 42.6 degrees N, 71.5 degrees W; geomagnetically 52 degrees N) in United States. The results show that the winds at Millstone Hill are more southward and more westward than those at Xinglong and Kelan in all seasons; the directional reversal time of zonal winds is also earlier at Millstone Hill than at the other two stations. Thermosphere-Ionosphere-Electrodynamics General Circulation Model shows better agreement with FPI observations in the winter months compared to summer, and in general best replicates those measurements taken at Millstone Hill. HWM14 generally produces agreement with quiet time midlatitude neutral wind measurements, with HWM14 meridional winds comparing very well throughout most of a year. HWM14 model-data discrepancies occur mainly in the zonal winds during the winter season. Overall, HWM14 predicts MH FPI observations slightly better than it does for the data from the two Asian stations.