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The University of Illinois Na wind/temperature lidar data collected at the Starfire Optical Range, New Mexico, can be used to present annual variations of the mesospheric mid-night horizontal winds. For each night, the winds profiles from the 11:00pm to 1:00am were smoothed in 1km altitude and then averaged in time to give mid-night winds profiles. All mid-night winds profiles within one month were averaged again to give mid night winds profiles of that month. The annual variations of the mid-night winds in the altitude ranges from 84km to 100km were obtained using a total of 46 nights lidar data distributed over the months except July. Zonal mid-night winds showed strong annual oscillations. Prevailing westerly winds blew over low altitudes in the winter months and over high altitudes in summer months. Meridional mid-night winds also showed annual or semi-annual oscillations. Southward winds dominated below 90km from April to October, and at about 96km during winter months and summer months except January. Correlations were found between the meridional mid-night winds and the mid-night temperatures. When the meridional winds blow from south, temperatures become warm. Results were compared with calculations of the HWM93 and the mid night winds observed with a MF radar at Urbana. Similar wind structures can be found in their results. The major differences are that strong westerly winds above 94km in March and April and strong northward winds at 96km in January were observed with the lidar. The winds values of the lidar and the MF radar data are larger than those of HWM93. Activities of inertial gravity waves and tidals might contaminated estimations of annual winds with the lidar data and contribute partially to their differences.
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