Vertical distribution of heat and sodium fluxes in the mesopause region measured by sodium lidar over Hainan, China (109° E, 19° N)

Abstract. We present the first lidar-based characterization of seasonal variations in gravity–wave induced vertical heat flux, sodium flux, and associated parameters – sodium density and temperature – between 80 and 100 km over Hainan, China (19° N, 109° E). Observations were carried out using a narrow band sodium lidar equipped with a laser frequency-locking and real-time monitoring module, achieving a root-mean-square (RMS) frequency stability of 0.5 MHz. Since February 2024, the system has provided continuous measurements of mesospheric sodium density, temperature, and vertical wind. The lidar results are generally consistent with coincident satellite measurements and model simulations at the near geographic location. Observations indicate that the highest temperatures below 95 km occur in May and November, with seasonal patterns closely matching from the SABER satellite data. The annual mean vertical heat flux shows two peak descent rates, −1.21 K m s−1 at 89 km and −1.38 K m s−1 at 92 km, corresponding to a cooling rate of approximately 95 K d−1 between 82 and 97 km. The sodium flux reveals pronounced maxima exceeding −65 m s−1 cm−3 at 92, with the resulting dynamical transport producing a maximum net sodium loss of 75 cm−3 h−1 near 93 km.