Fig. 1. Density variations of the middle atmosphere measured with lidar over Haikou at night on July 3, 2011

Fig. 2. Retrieval and comparison of temperature in the middle atmosphere. (a) Temperature structure of the middle atmosphere measured with lidar over Haikou at night on July 3, 2011; (b) comparison between temperature profile measured by lidar and the results from NRLMSISE-00, SABER/TIMED, and COSMIC

Fig. 3. Relative temperature perturbation in the middle atmosphere measured by lidar over Haikou at night on July 3, 2011

Fig. 4. Vertical power spectra and temporal frequency spectra of gravity wave activities observed with lidar over Haikou at night on July 3, 2011. (a) Vertical power spectra; (b) temporal frequency spectra

Fig. 5. Data analysis process for mesospheric temperature retrieval and gravity wave event identification according to lidar observations

Fig. 6. Temperature structure retrieval results during the cloud occurrence. (a) Sequence of Rayleigh scattering profiles acquired by Hainan lidar station at night on May 2, 2011, and invalid profiles are drawn with dashes; (b) temperature structure retrieved without invalid data

Fig. 7. Statistic results of gravity wave events observed with lidar over Haikou from January 2011 to July 2013. (a) Characteristic vertical wavelengths of gravity wave events; (b) characteristic wave periods of gravity wave events; (c) histogram of vertical wavelengths; (d) histogram of wave periods